အီလက္ထေရာနစ္ နည္းပညာ

DC/AC Pure Sine Wave Inverter

2011-09-19T20:38:00.000-07:00

ကိုေက်ာ္ဆန္းကိုကို ေမးထားတဲ့ Sine Wave Inverter Circuit အေၾကာင္းDownload Here.

0-30 VDC Stabilized power supply with current control 0.002-3 A

2011-04-21T19:00:00.000-07:00

General Description

This is a high quality power supply with a continuously variable stabilised output adjustable at any value between 0 and 30VDC. The circuit also incorporates an electronic output current limiter that effectively controls the output current from a few milliamperes (2 mA) to the maximum output of three amperes that the circuit can deliver. This feature makes this power supply indispensable in the experimenters laboratory as it is possible to limit the current to the typical maximum that a circuit under test may require, and power it up then, without any fear that it may be damaged if something goes wrong.

There is also a visual indication that the current limiter is in operation so that you can see at a glance that your circuit is exceeding or not its preset limits.

Technical Specifications - Characteristics

Input Voltage: ................ 24 VAC
Input Current: ................ 3 A (max)
Output Voltage: ............. 0-30 V adjustable
Output Current: ............. 2 mA-3 A adjustable
Output Voltage Ripple: . 0.01 % maximum

FEATURES

Reduced dimensions, easy construction, simple operation.
Output voltage easily adjustable.
Output current limiting with visual indication.
Complete protection of the supplied device against over loads and malfunction.

How it Works

To start with, there is a step-down mains transformer with a secondary winding rated at 24 V/3 A, which is connected across the input points of the circuit at pins 1 & 2. (the quality of the supplies output will be directly proportional to the quality of the transformer). The AC voltage of the transformers secondary winding is rectified by the bridge formed by the four diodes D1-D4. The DC voltage taken across the output of the bridge is smoothed by the filter formed by the reservoir capacitor C1 and the resistor R1. The circuit incorporates some unique features which make it quite different from other power supplies of its class. Instead of using a variable feedback arrangement to control the output voltage, our circuit uses a constant gain amplifier to provide the reference voltage necessary for its stable operation. The reference voltage is generated at the output of U1. The circuit operates as follows: The diode D8 is a 5.6 V zener, which here operates at its zero temperature coefficient current. The voltage in the output of U1 gradually increases till the diode D8 is turned on. When this happens the circuit stabilises and the Zener reference voltage (5.6 V) appears across the resistor R5. The current which flows through the non inverting input of the op-amp is negligible, therefore the same current flows through R5 and R6, and as the two resistors have the same value the voltage across the two of them in series will be exactly twice the voltage across each one. Thus the voltage present at the output of the op-amp (pin 6 of U1) is 11.2 V, twice the zeners reference voltage. The integrated circuit U2 has a constant amplification factor of approximately 3 X, according to the formula A=(R11+R12)/R11, and raises the 11.2 V reference voltage to approximately 33 V. The trimmer RV1 and the resistor R10 are used for the adjustment of the output voltages limits so that it can be reduced to 0 V, despite any value tolerances of the other components in the circuit. Another very important feature of the circuit, is the possibility to preset the maximum output current which can be drawn from the p.s.u., effectively converting it from a constant voltage source to a constant current one. To make this possible the circuit detects the voltage drop across a resistor (R7) which is connected in series with the load. The IC responsible for this function of the circuit is U3. The inverting input of U3 is biased at 0 V via R21. At the same time the non inverting input of the same IC can be adjusted to any voltage by means of P2. Let us assume that for a given output of several volts, P2 is set so that the input of the IC is kept at 1 V. If the load is increased the output voltage will be kept constant by the voltage amplifier section of the circuit and the presence of R7 in series with the output will have a negligible effect because of its low value and because of its location outside the feedback loop of the voltage control circuit. While the load is kept constant and the output voltage is not changed the circuit is stable. If the load is increased so that the voltage drop across R7 is greater than 1 V, IC3 is forced into action and the circuit is shifted into the constant current mode. The output of U3 is coupled to the non inverting input of U2 by D9. U2 is responsible for the voltage control and as U3 is coupled to its input the latter can effectively override its function. What happens is that the voltage across R7 is monitored and is not allowed to increase above the preset value (1 V in our example) by reducing the output voltage of the circuit. This is in effect a means of maintaining the output current constant and is so accurate that it is possible to preset the current limit to as low as 2 mA. The capacitor C8 is there to increase the stability of the circuit. Q3 is used to drive the LED whenever the current limiter is activated in order to provide a visual indication of the limiters operation. In order to make it possible for U2 to control the output voltage down to 0 V, it is necessary to provide a negative supply rail and this is done by means of the circuit around C2 & C3. The same negative supply is also used for U3. As U1 is working under fixed conditions it can be run from the unregulated positive supply rail and the earth. The negative supply rail is produced by a simple voltage pump circuit which is stabilised by means of R3 and D7. In order to avoid uncontrolled situations at shut-down there is a protection circuit built around Q1. As soon as the negative supply rail collapses Q1 removes all drive to the output stage. This in effect brings the output voltage to zero as soon as the AC is removed protecting the circuit and the appliances connected to its output. During normal operation Q1 is kept off by means of R14 but when the negative supply rail collapses the transistor is turned on and brings the output of U2 low. The IC has internal protection and can not be damaged because of this effective short circuiting of its output. It is a great advantage in experimental work to be able to kill the output of a power supply without having to wait for the capacitors to discharge and there is also an added protection because the output of many stabilised power supplies tends to rise instantaneously at switch off with disastrous results.

Construction

First of all let us consider a few basics in building electronic circuits on a printed circuit board. The board is made of a thin insulating material clad with a thin layer of conductive copper that is shaped in such a way as to form the necessary conductors between the various components of the circuit. The use of a properly designed printed circuit board is very desirable as it speeds construction up considerably and reduces the possibility of making errors. To protect the board during storage from oxidation and assure it gets to you in perfect condition the copper is tinned during manufacturing and covered with a special varnish that protects it from getting oxidised and also makes soldering easier.

Soldering the components to the board is the only way to build your circuit and from the way you do it depends greatly your success or failure. This work is not very difficult and if you stick to a few rules you should have no problems. The soldering iron that you use must be light and its power should not exceed the 25 Watts. The tip should be fine and must be kept clean at all times. For this purpose come very handy specially made sponges that are kept wet and from time to time you can wipe the hot tip on them to remove all the residues that tend to accumulate on it.

DO NOT file or sandpaper a dirty or worn out tip. If the tip cannot be cleaned, replace it. There are many different types of solder in the market and you should choose a good quality one that contains the necessary flux in its core, to assure a perfect joint every time.

DO NOT use soldering flux apart from that which is already included in your solder. Too much flux can cause many problems and is one of the main causes of circuit malfunction. If nevertheless you have to use extra flux, as it is the case when you have to tin copper wires, clean it very thoroughly after you finish your work.

In order to solder a component correctly you should do the following:

Clean the component leads with a small piece of emery paper.
Bend them at the correct distance from the components body and insert he component in its place on the board.
You may find sometimes a component with heavier gauge leads than usual, that are too thick to enter in the holes of the p.c. board. In this case use a mini drill to enlarge the holes slightly. Do not make the holes too large as this is going to make soldering difficult afterwards.
Take the hot iron and place its tip on the component lead while holding the end of the solder wire at the point where the lead emerges from the board. The iron tip must touch the lead slightly above the p.c. board.
When the solder starts to melt and flow wait till it covers evenly the area around the hole and the flux boils and gets out from underneath the solder.
The whole operation should not take more than 5 seconds. Remove the iron and allow the solder to cool naturally without blowing on it or moving the component. If everything was done properly the surface of the joint must have a bright metallic finish and its edges should be smoothly ended on the component lead and the board track. If the solder looks dull, cracked, or has the shape of a blob then you have made a dry joint and you should remove the solder (with a pump, or a solder wick) and redo it. Take care not to overheat the tracks as it is very easy to lift them from the board and break them.
When you are soldering a sensitive component it is good practice to hold the lead from the component side of the board with a pair of long-nose pliers to divert any heat that could possibly damage the component.
Make sure that you do not use more solder than it is necessary as you are running the risk of short-circuiting adjacent tracks on the board, especially if they are very close together.
When you finish your work, cut off the excess of the component leads and clean the board thoroughly with a suitable solvent to remove all flux residues that may still remain on it.

connections.gif (17,8KB)

pcb.gif (60KB) (12,5cm x 8,7cm)

layout.gif (92KB)

As it is recommended start working by identifying the components and separating them in groups. Place first of all the sockets for the ICs and the pins for the external connections and solder them in their places. Continue with the resistors. Remember to mound R7 at a certain distance from the printed circuit board as it tends to become quite hot, especially when the circuit is supplying heavy currents, and this could possibly damage the board. It is also advisable to mount R1 at a certain distance from the surface of the PCB as well. Continue with the capacitors observing the polarity of the electrolytic and finally solder in place the diodes and the transistors taking care not to overheat them and being at the same time very careful to align them correctly.

Mount the power transistor on the heatsink. To do this follow the diagram and remember to use the mica insulator between the transistor body and the heatsink and the special fibber washers to insulate the screws from the heatsink. Remember to place the soldering tag on one of the screws from the side of the transistor body, this is going to be used as the collector lead of the transistor. Use a little amount of Heat Transfer Compound between the transistor and the heatsink to ensure the maximum transfer of heat between them, and tighten the screws as far as they will go.

Attach a piece of insulated wire to each lead taking care to make very good joints as the current that flows in this part of the circuit is quite heavy, especially between the emitter and the collector of the transistor.

It is convenient to know where you are going to place every thing inside the case that is going to accommodate your power supply, in order to calculate the length of the wires to use between the PCB and the potentiometers, the power transistor and for the input and output connections to the circuit. (It does not really matter if the wires are longer but it makes a much neater project if the wires are trimmed at exactly the length necessary).

Connect the potentiometers, the LED and the power transistor and attach two pairs of leads for the input and output connections. Make sure that you follow the circuit diagram very care fully for these connections as there are 15 external connections to the circuit in total and if you make a mistake it may be very difficult to find it afterwards. It is a good idea to use cables of different colours in order to make trouble shooting easier.

The external connections are:

1 & 2 AC input, the secondary of the transformer.
3 (+) & 4 (-) DC output.
5, 10 & 12 to P1.
6, 11 & 13 to P2.
7 (E), 8 (B), 9 (E) to the power transistor Q4.
The LED should also be placed on the front panel of the case where it is always visible but the pins where it is connected at are not numbered.

When all the external connections have been finished make a very careful inspection of the board and clean it to remove soldering flux residues. Make sure that there are no bridges that may short circuit adjacent tracks and if everything seems to be all right connect the input of the circuit with the secondary of a suitable mains transformer. Connect a voltmeter across the output of the circuit and the primary of the transformer to the mains.
DO NOT TOUCH ANY PART OF THE CIRCUIT WHILE IT IS UNDER POWER.

The voltmeter should measure a voltage between 0 and 30 VDC depending on the setting of P1, and should follow any changes of this setting to indicate that the variable voltage control is working properly. Turning P2 counter-clockwise should turn the LED on, indicating that the current limiter is in operation.

Adjustments

If you want the output of your supply to be adjustable between 0 and 30 V you should adjust RV1 to make sure that when P1 is at its minimum setting the output of the supply is exactly 0 V. As it is not possible to measure very small values with a conventional panel meter it is better to use a digital meter for this adjustment, and to set it at a very low scale to increase its sensitivity.

Warning

While using electrical parts, handle power supply and equipment with great care, following safety standards as described by international specs and regulations.

CAUTION

This circuit works off the mains and there are 220 VAC present in some of its parts.
Voltages above 50 V are DANGEROUS and could even be LETHAL.
In order to avoid accidents that could be fatal to you or members of your family please observe the following rules:

DO NOT work if you are tired or in a hurry, double check every thing before connecting your circuit to the mains and be ready
to disconnect it if something looks wrong.
DO NOT touch any part of the circuit when it is under power.
DO NOT leave mains leads exposed. All mains leads should be well insulated.
DO NOT change the fuses with others of higher rating or replace them with wire or aluminium foil.
DO NOT work with wet hands.
If you are wearing a chain, necklace or anything that may be hanging and touch an exposed part of the circuit BE

CAREFUL.

ALWAYS use a proper mains lead with the correct plug and earth your circuit properly.
If the case of your project is made of metal make sure that it is properly earthen.
If it is possible use a mains transformer with a 1:1 ratio to isolate your circuit from the mains.
When you are testing a circuit that works off the mains wear shoes with rubber soles, stand on dry non conductive floor
and keep one hand in your pocket or behind your back.
If you take all the above precautions you are reducing the
risks you are taking to a minimum and this way you are protecting
yourself and those around you.
A carefully built and well insulated device does not constitute any danger for its user.
BEWARE: ELECTRICITY CAN KILL IF YOU ARE NOT CAREFUL.

If it does not work

Check your work for possible dry joints, bridges across adjacent tracks or soldering flux residues that usually cause problems.
Check again all the external connections to and from the circuit to see if there is a mistake there.

See that there are no components missing or inserted in the wrong places.
Make sure that all the polarised components have been soldered the right way round. - Make sure the supply has the correct voltage and is connected the right way round to your circuit.
Check your project for faulty or damaged components.

Electronic Diagram.

Parts List.
R1 = 2,2 KOhm 1W
R2 = 82 Ohm 1/4W
R3 = 220 Ohm 1/4W
R4 = 4,7 KOhm 1/4W
R5, R6, R13, R20, R21 = 10 KOhm 1/4W
R7 = 0,47 Ohm 5W
R8, R11 = 27 KOhm 1/4W
R9, R19 = 2,2 KOhm 1/4W
R10 = 270 KOhm 1/4W
R12, R18 = 56KOhm 1/4W
R14 = 1,5 KOhm 1/4W
R15, R16 = 1 KOhm 1/4W
R17 = 33 Ohm 1/4W
R22 = 3,9 KOhm 1/4W
RV1 = 100K trimmer
P1, P2 = 10KOhm linear pontesiometer
C1 = 3300 uF/50V electrolytic
C2, C3 = 47uF/50V electrolytic
C4 = 100nF polyester
C5 = 200nF polyester
C6 = 100pF ceramic
C7 = 10uF/50V electrolytic
C8 = 330pF ceramic
C9 = 100pF ceramic
D1, D2, D3, D4 = 1N5402,3,4 diode 2A - RAX GI837U
D5, D6 = 1N4148
D7, D8 = 5,6V Zener
D9, D10 = 1N4148
D11 = 1N4001 diode 1A
Q1 = BC548, NPN transistor or BC547
Q2 = 2N2219 NPN transistor
Q3 = BC557, PNP transistor or BC327
Q4 = 2N3055 NPN power transistor
U1, U2, U3 = TL081, operational amplifier
D12 = LED diode

Scrolling LED sign based on Atmel ATtiny2313 AVR microcontrolle

2010-08-10T20:57:00.000-07:00

On this page you will find a scrolling LED sign based on the ATtiny2313 AVR microcontroller, which you can build yourself (when finished) Other names for this device can be: Moving message sign, Message crawler, Scrolling message, message display, etc.
The idea is to let a text scroll over the LED dot-matrix displays. A dot-matrix display is a display which contains 5x7 dots (LEDs) in one case, the LEDs are connected like a matrix, there are two types CC and CA, the LEDs are simply put the other way around, here the drawings (inside and front):

If you put 1.8 Volt e.g. at the lines 4 and 10, that LED (dot) will lit, the trick of multiplexing is to scan the columns (5) and set the data on the rows (7) (or visa-versa), the multiplex-frequency must be greater than approx. 40Hz else you will see the flickering of the LEDs to much (take about 5 msec per column, thats about 25 msec for one frame)
The scanning goes as follows, first set the rows data on the 7 rows e.g. 1010010, then activate (0 or 1 -> depends on which type CA = common cathode, or CC = common anode) the first column, now these LEDs (dots) will lit, wait 5 msec, then switch the column off, now load the next rows data, and set the second column on, wait 5 msecs again, and switch it off again, if you repeat this sequence very fast, you will see the data (character data) appear on the display (refresh frequency 40 - 70Hz is ok, don't take twice or half the artificial light-frequency of 50/60 Hz)
The rows data comes e.g. from the EEPROM or flash memory of the AVR, you can also take an external EEPROM/flash IC, the ATtiny2313 has 128 bytes EEPROM and 2k of flash memory, what you can do is put the character data (ASCII) into the flash memory (read below for more details) Next the test-diagram:

The 74HC595 is an 8-bit shift-register IC, with this IC you can shift 8 bits to the outputs with only 3 wires, that are Data (Ds), and 2 shift inputs (SHcp, STcp), connect like the diagram. How does the 74HC595 works? First shift the 8 bits into the stages with SHcp, then shift the stages to the outputs with STcp, this causes the outputs to switch in one go, with e.g. a 74HCT164 you can only shift the bits into the outputs, the advantage of the 74HC595 is the storage register. Don't forget that multiplexing causes the LEDs only lit up for a fraction, so if you want the same intensity you must put more current through them, this diagram is for practice and programming, wants you have it working you can put transistors and resistors on. Here I put the letter R on the display as you can see, using a little breadboard: (next: How the scrolling is done...)

How to scroll a character accross the display ? The trick is to build one character on the display by scanning the columns very fast, and let say each 20 times (20 frames) scroll it one position to the left, this will give the effect of a walking text accross the dot-matrix display. So first build one frame, repeat this 20 times, and after that, read the data one address later, if you do this 5 times (5 columns) the character scroll from right to left from the display. (the refresh goes so fast that your brain can't keep up, and what you see is the R scrolling over the display) Btw, I will take five 74HC595's shiftregisters IC's, that are 5 x 8 bit = 40 bits / 5 columns = 8 dot-matrix displays, making it a nice tiny message sign.

What I am going to do is putting ASCII data (thats 128 x 5 bytes = 640 bytes) into the 2k flash memory of the ATtiny2313, then I have 704 words left for my program, that can really be a huge program!, because I used only 69 lines (69 instructions) of program so far, and that scrolls characters fluently accross the dot-matrix display. I made the program so that you can set the scroll-speed, from 0 - 255, so 256 speeds, 25 fps (frames/second) is a nice speed. On one of my pages (this page) I am using a 2-bit Gray code rotary encoder, with this encoder I will make an edit function in the software, so you can edit messages, without a keyboard, this save space, this type of rotary encoder has a push-function in the shaft, so e.g. after you select a character you can store that in memory.

A Digital, Up / Down Counter

2010-08-10T20:35:00.000-07:00

Origionally I designed this for use on my Metal Laithe to Aid in winding coils.
But it can be adapted for many other applications.

This Circuit uses a CD40110BE, Up/Down Counter IC's.
The CD40110BE is Available from Digi-Key
Digi-Key Part Number "296-3506-5-ND"

**** DO NOT CONFUSE THIS IC WITH A CD4011 ****

This IC is able to Source Each Segment with 25 mA, Giving a Very Nice Bright Display.
The 7 Segment Displays MUST be a Common Cathode Type, as I have used here

NOTE Also : All the UnMarked Resistors should be at least 680 Ohms for Up To 12 Volts Supply Voltage.

For Higher Supply Voltages up to 18 volts or Reduced Currents, I would suggest Increasing these Values to 1500 Ohms.

Or if you want "Reduced Power" and "Brightness", Adjust the resistor values as appropriate.
Basically the Approximate Current is Supply voltage Minus 2, Divided by the Resistor Value.

The Schematic posted here Only shows the First, Second, Third and Last Stages.
And This board is for a counter of up to 9999.

However: Since All Stages between the Third and Last, Would be the same,
So you could make a display with as many digits as you wish, by expanding the circuit board.

Additionally: You can just put in 1, 2, 3, or all 4 IC's and the Appropriate Displays.

Other Options:

Adding a Clock Circuit with a Frequency of 1 Hz in place of the Reset Switch will create a Frequency counter in Hz/Sec.
Adding a Clock Circuit with a Frequency of 1 Hz into one of the Inputs can create an up or down counter type of timer.
Although Not Highly Accurate, a Simple 555 circuit will work as a Simple Clock.

Home security system

2010-06-07T19:22:00.000-07:00

The security system application and program offers a simple demonstration of the BASIC Serial Interface. By adding only a few door and window switches, a transistor, a siren, (see schematic) and a few lines of BASIC program (see program listing) the interface can become a multi-function security system. Please note, however, that it is a "barebones" program. It is left to the reader to fancy it up to their liking.

Normally closed door and window switches can be attached to the interface "in" ports as shown in the schematic(all unused ports should be grounded). In this configuration with all the switches closed the "in" port is held "low". When any switch opens the port goes "high". The program recognizes this as an alarm condition for the zone associated with that port. If the program "detects" a high on "in" port number 1 it will delay sounding the alarm for a user defined length of time. This is done to allow the owner time to enter the secured area and reset the alarm before the siren is activated. If a "high" condition is detected on any of the other ports, 2 to 7, an alarm will be sounded immediately.

The alarm is sounded by bringing "out" port number 1 high. Connected to "out" port 1 is a NPN transistor which switches a 12 volt supply to a security siren or bell (figure 3) . The.alarm remains on until the system is reset or it reaches it's time out period.

In order for the BSI to transmit the status of it's "in" ports Data Strobe (pin. 23 of IC1) must be toggled. This toggling of the Data Strobe is done by program control. In this application Data Strobe is connected to "out" port 8 by a jumper. In order to trigger a transmission of the port conditions the program turns "out" port8 "on" then "off". This causes IC1 to transmit the status of it's "in" ports.

10 ' BASIC SERIAL INTERFACE
20 '
30 ' SECURITY SYSTEM DMONSTRATION PROGRAM
40 '
50 ' setup
60 KEY OFF:CLS:CLOSE'......................................... turn key off, clear screen, close
70 OPEN "COM1:1200,N,8,2" AS #1' .......................all files, open the serial port
80 PRINT#1,CHR$(NUL);'.........................................as com port #1, and transmit "0".
90 GOTO 310
100 '
110 FOR X=1 TO 8'.................................................. Subroutine to convert decimal number
120 B=C MOD 2:C=INT(C/2):R(X)=B'...................... received from the UART to binary
130 NEXT X'............................................................. and set array variables to represent
140 RETURN'.............................................................UART port conditions,R(1) to R(8)
150 REM
160 IF T(HP)=1 THEN 210'.......................................Subroutine to turn one UART port on
170 FOR X=1 TO 8'..................................................without changing the condition of
180 IF HP=X THEN OT=OT+2^(X-1):T(X)=1'...............any other UART port.---
190 NEXT X
200 PRINT #1,CHR$(OT);
210 RETURN
220 '
230 IF T(HP)=0 THEN 280'........................................Subroutine to turn one UART port off
240 FOR X=1 TO 8'...................................................without changing the condition of
250 IF HP=X THEN OT=OT-2^(X-1):T(X)=0'................any other port.---
260 NEXT X
270 PRINT #1,CHR$(OT);
280 RETURN
290 '********************* SECURITY SYSTEM MAIN PROGRAM *******
300 '
310 PRINT" Security System Program
320 '
330 PRINT:PRINT"Note:'OUT' port 8 of the UART (pin 5) must be connected to Data Strobe (pin 23)before running this program.":PRINT
340 INPUT"ENTER ALARM DELAY FOR ZONE #1 ENTRY ";DELAY
350 INPUT"ENTER ALARM TIMEOUT ";TIMEOUT
360 '
370 CLS:PRINT#1,CHR$(128);'.................................clear screen and turn UART port 8 on
380 PRINT "Ctrl E to reset"
390 HP=8 :GOSUB 220:HP=8:GOSUB 150'................Ask UART for 'in' port status.
400 IF LOC(1)=0 THEN 470'.......................................If transmission not received,skip.
410 IN$=INPUT$(1,#1):C=ASC(IN$):GOSUB 100'... read transmission and convert to
420 FOR X=1 TO 8'......................................................binary,assign each bit to array R(X)
430 LOCATE X+9,10
440 IF R(X)=1 THEN PRINT X;" ALARM !!!!!"' Print UART port status conditions
450 IF R(X)=0 THEN PRINT X;" ZONE SECURE"' as either 'alarm' or 'secure'
460 NEXT X
470 IF R(1)=1 THEN TIME=TIME+'.............................If zone 1 is high start delay time.
480 IF TIME=DELAY THEN ALARM=1'.......................if delay time is up set alarm.
490 FOR X=2 TO 8
500 IF R(X)=1 THEN ALARM=1'..................................if any zone,2-8,is high,set alarm.
510 NEXT X
520 IF ALARM=1 THEN HP=1:GOSUB 150'............... if alarm set,turn port 1 on.
530 IF ALARM=1 THEN RESETT=RESETT+1'............ if alarm is set start timeout.
540 IF RESETT=TIMEOUT THEN GOTO 580'............ If timeout is up then shutdown.
550 A$=INKEY$:IF A$="" THEN 570'........................ Check to see if Ctrl E was entered,
560 IF ASC(A$)=5 THEN 50'...................................... if it was then reset program.
570 GOTO 390
580 PRINT#1,CHR$(NUL);'.......................................Turn alarm off
590 PRINT:PRINT"SYSTEM SHUTDOWN AT "TIME$,DATE$ ' print shutdown
600 END

12 VOLT FLASHING BEACON

2010-03-13T00:58:00.000-08:00

Note: The lamp shown is not supplied unless requested. A festoon bulb is supplied.

Note: Aligator clips may replace the auto plug.

Schematic Diagram

PCB Layout

Construction

1. Make a visual check of the PC board for damage in transit. Look for small breaks and/or other damage to tracks. The green coating on the tracks should be left in place as it protects the tracks from oxidation or corrosion, and it does not inhibit soldering in any way. A multi-meter or Electronic Circuit Tester can be used to test continuity of the tracks.

2. A Circuit Board Holder is useful in freeing both hands for mounting and soldering the components. A spring board clip can be screwed down and will hold the board securely. Wooden blocks with a suitable groove, and able to slide (say on two pieces of dowel) to adjust to the varying lengths of PC Board also work well. Commercially produced stands are available, with an alternative magnifying glass. (types and prices available).

3. Mounting the components is relatively easy. The resistors will have to have the legs bent to match their holes. They may either be mounted to stand vertically or flush on the PCB, except, please note that R5 must be mounted flat on the board to clear under the body of the power transistor.

4. The power diode has a band at the neg (K) end. Polarity must be observed. (This diode is there to protect the unit from the effects of connecting it to the battery in the wrong polarity). The Electrolytic Capacitor also is polarised. There is an arrow on the body pointing down the negative (K) leg. You will notice that the Trimpot has one outside and centre legs joined in the track. This is correct; the other outside leg goes to the other track as indicated.

5. The small Transistor (BC558) has a flat on the body. The transistor is mounted with the flat towards the large transistor. The Power Transistor (2N3055) will fit the holes perfectly, so it is unlikely you will mount it the wrong way round. Note that one hole in the track is drilled D3mm to match the hole in the metal body. The metal body is the Collector (C) of this transistor. Use the 3mm machine screw and two nuts to join it to the track. Feed the screw down through the transistor hole and put a nut top and bottom of the PCBoard. The legs can then be soldered.

6. The six pins can be pushed into their holes. Soldering Technique is most important.

7. If you are fitting a switch to allow the unit to be have a trouble light mode then this switch is connected (by wires) to Pins 2 and 3.

8. Test the unit and adjust the flash rate with the trimpot. N.B.: This unit will work only on FULLY RECTIFIED CURRENT. It will NOT work from a power-pak plugged into a power outlet. A car battery is best but a 9Volt battery will work. If the unit doesn't work, check polarity of all components (diode,capacitor,transistors). Check the colour bands to ensure resistors are in correct places. Check that the trimpot bridges across the tracks with one outside and centre legs. Visually check soldering; resolder any suspect joints. Check for bridges of solder between tracks and remove them. The circuit is reliable and robust. Exercise meticulous care in putting it together and it will fire up first time.

If you are electing to construct the Flashing Beacon via the template/insulator method, the template appears below

INFRA-RED DOOR ALARM

2009-11-19T05:16:00.000-08:00

Transmitter Construction

Inspect the tracks for fine breaks and test the continuity of each track with an electronic circuit tester or ohm-meter.
Identify the four resistors and insert them in the PCB according to the PCB Layout diagram.
The 8 pin IC socket can be pushed carefully into place. Solder in place.
There are two capacitors. Their values are marked on the body, they can go in any way round. Solder in place.
The four PCB pins can be inserted and soldered.
The IR LED can be identified by it's purple colour.Observe polarity and insert and solder,
The second LED is inserted and soldered, observing polarity.
The switch can be located and soldered.
Find the locating DOT on the 555 IC and arrange it as the drawing shows. To fit the 555 it will probably be necessary to bend the legs inwards a little by placing one set of legs on a flat surface and push down lightly. This will maintain their alignment. Repeat for the other side of the chip so they match the socket. Push the IC into place.
The battery snap can be soldered to the pins.
The transmitter uses a 3V power source. The 2 x AA battery holder is used for the transmitter. Connect the batteries.
When the switch is in the ON opsition, the LED will illuminate.

Trouble shooting

Troubleshooting if necessary will involve careful checking of locations and polarity of components, mainly the LED polarity and the locating DOT on the 555 IC is as the drawing shows. Re-solder all joints and check to make sure you have not bridged across between any two adjacent component legs. The end of a broken hacksaw blade sharpened on an emery wheel is a good tool for cleaning between soldered joints.

Receiver Construction

Inspect the tracks for fine breaks and test the continuity of each track with an electronic circuit tester or ohm-meter.
Insert the capacitor and solder.
Insert the transistor observing orientation, solder in place.
Insert and solder the PCB pins.
Locate the switch and solder.
Connect the buzzer wires to the PCB pins.
Insert the IR receiver and solder.
Connect the battery holder to the PCB pins.
Insert the batteries. When the receiver is on, the buzzer will sound.

Setting up

Arrange the transmitter and receiver about 1 metre apart with the IR LED of the transmitter pointing in the direction of the receiver
Orientate the receiver so that the IR decoder is facing the transmitter.
Turn the receiver ON - the buzzer will sound.
Turn the transmitter on and the buzzer should stop. If not check the orientation of both transmitter and receiver.
If you place your hand (or some object) in the beam, the buzzer will sound.
This unit has a range of 2 - 3 metres.

Trouble shooting

Troubleshooting if necessary will involve careful checking of locations and polarity of components. Re-solder all joints and check to make sure you have not bridged across between any two adjacent component legs. The end of a broken hacksaw blade sharpened on an emery wheel is a good tool for cleaning between soldered joints.

Technical notes

Looking at the transmitter, the 555 creates a 50 kHz signal which is used to power the IR LED. This sends a beam of infra-red light.

The frequency of oscillation can be calculated using the following formula:

The receiver is primarily made up of the IR decoder. This component receives the IR transmission and converts it back into the 50 kHz signal that was generated by the transmitter - appearing at the Data pin. This signal is filtered by the capacitor which stores enough energy to maintain the status of the transistor in the off position until the next signal pulse (50 kHz - 50 000 times a second).

When the beam is broken, the transistor is energised and the buzzer sounds.

Touch activated alarm system

2009-11-02T23:27:00.000-08:00

Parts List
R1 = 100K D1 = 1N4004, (or any other 1N4001,2,etc) general purpose diode
R2 = 4K7 C1 = 47uF/16V, electrolytic
R3 = 10M C2 = 0.1uF (100nF) ceramic
P1 = 100K IC1 = 555 Timer
Ry = Relay Q1 = 2N3904, 2N2222, or similar

Additional Notes
Not much to tell here as the circuit speaks for itself. The 555 can be almost any type, they are all pin-compatible. Although some CMOS types may not have enough power to drive the transistor, in that case use an ordinary 555. C1's working voltage should be increased to 25V if you decide to go with a 12V power source. Change the value of C1 for the desired output pulse.

For the timing use this equation: T=1.1*(R1+P1)*C1 assuming R1 + P1 = 150K, then select C1 as follows: C1 = 6uF for each 1-second pulse width. For example, if you want the pulse width to be 5 seconds, C1 should be 30uf or nearest value like 22 or 33uF. Additionally, P1 can adjust the rest.
Rule of thumb: the working voltage of capacitors are at least double the supplied voltage, in other words, if the power source is 9Volt, your capacitor(s) is at least 18V. Transistor T1 can be any approximate substitute. Use any suitable relay for your project and if you're not tight on space, use any size. I've build this particular circuit to prevent students from fiddling with the security cameras in computer labs at the University I am employed. I made sure the metal casing was not grounded. But as the schematic shows you can basically hook it up to any type of metal surface. I used a 12-vdc power source. Use any suitable relay to handle your requirements. A 'RESET' switch (Normally Closed) can be added between the positive and the 'arrow-with-the-+'. The trigger (touch) wire is connected to pin 2 of the 555 and will trigger the relay, using your body resistance, when touched. It is obvious that the 'touching' part has to be clean and makes good contact with the trigger wire. This particular circuit may not be suitable for all applications. Just in case you wonder why pin 5 is not listed in the schematic diagram; it is not really needed. In certain noisy conditions a small 0.01uF ceramic capacitor is placed between pin 5 and ground. It does no harm to add one or leave it out.

NOTE: For those of you who did not notice, there is an approximate 5-second delay build-in before activation of the relay to avoid false triggering, or a 'would-be' thief, etc.

AGAIN, make sure the latch (pin 2) is not touching anything 'ground' or the circuit just keeps resetting itself and so will not work. My shed has wooden doors so works fine. If you can't get yours to work, check the trigger input, verify there is some sort of signal coming from output pin 3, play with the value of R3/C1, etc.
The original circuit, as submitted by W. Knight to Hands-on magazine, was as shown below. R2 is replaced by the two resistors and the 33uF capacitor for the delay.

Motion Triggered Spy Cam

2009-11-02T21:21:00.000-08:00

step 1

What You Need...

1. Motion Sensing Door Chime. Radio Shack Part #49-426
2. Mini Spy Cam DVR from Ebay
3. 200uF Capacitor
4. Any Reed Relay
5. Diode 1N4001, 1N4007, etc.
6. Momentary Switch

step 2

Prepare the Motion Sensor

Disasemble the Motion Sensor. There is opnly one screw under the battery compartment. Remove it and then pry apart the case. Cut or desolder the speaker leads and the external output cable and connector. This should leave you with just the circuit board and the 9V power connector.

step 3

Assemble the Components

Time to assemble the components that link the motion sensor and the DVR. Follow the included schematic. 1. Solder the diode to the reed relay paying attention to the cathode (-) position. The purpose of the diode is to prevent voltage flow back into the circuit when the relay is triggered. 2. Solder the capacitor to the diode. Again, pay attention to the striped (-) marking on the capacitor. The purpose of the capacitor is to turn the relay into a temporary switch by limiting the voltage pulses to a single pulse rather than the continual pulses the alarm gives out. 3. Make your connection from the (+) side of the cap to J2 on the circuit board. J2 is the trigger point for the motion sensor. 4. Make your connection from the anode (+) side of the diode to ground located where the 9V wires are at J5 on the circuit board. 5. Run two wires from the outside contacts on the relay to your switch. The switch allows you to stop recordin and power off the DVR.

step 4

Prepare the DVR

This is tricky. On the end of the mini DVR is a super-micro push button switch that must be de-soldered and removed. This may require an assistant to carefully lift up on each side with a tiny screwdriver as you heat the contacts. Once the switch is removed, solder two leads to the two contacts. Then wire the two leads to the outside contact on the reed relay. Done!

step 5

Test it Out

At this point you should be able to press the momentary switch and the DVR should power up (yellow indicator) and begin recording (blue indicator). Then attach a 9v battery and slide the switch on the motion sensor to the alarm position. (towards the 9v wires). There is a built-in 15 second delay when you turn it on to allow you to place the sensor and walk away. After that you should be able to wave your hand across the sensor and the DVR should power up and begin recording. While the sensor lens increases the range to around 30', eliminating it will reduce that distance so keep that in mind when you place it in service. The DVR is USB based. The movie files (352 X 288 12fps) are located in the "movies' folder when you plug in the DVR to your computer. Have Fun, Be Safe and use responsibly.

World's Loudest Alarm Clock!

2009-09-25T23:45:00.000-07:00

TOUCH Switch

2009-07-27T20:23:00.000-07:00

All the circuits and projects we describe in these articles consist of very important "building blocks" that you can add to other designs.

This time we describe the concept of touching a plate (or two plates separated by a small gap) and turning a circuit ON or OFF.

A TOUCH PLATE is classified as a high impedance device (or high impedance circuit) as the effect of a finger will be detected by the circuit connected to the plate.

To learn more about the concept of high impedance circuits, see Page 77 of our Basic Electronics course.
If only a single plate is present, the circuit will actually be picking up "mains hum" from the finger. To prove this, take the project into an open space such as a large park and try the circuit. It will not work.

If the plate has a signal on it (from an oscillator), the effect of your finger will be to remove the signal (or reduce its amplitude considerably) and a detecting circuit will be activated.

If the circuit has two plates, it will be registering the resistance of your finger. If the circuit has 4 plates, it will use two to turn the circuit ON and two to turn the circuit OFF.

There are a number of different types of TOUCH PLATES and different effects can be created by the circuit.

1. Touch a set of pads and the project turns on. When the finger is removed, the circuit turns off. The finger can touch the pads for any length of time. We also include the feature where the circuit extends the ON period, so the circuit stays on for a length of time after the finger is removed. This is shown in Circuits A.

2. Touch a set of pads fairly quickly and the project turns on. Touch the pads again for a short period of time and the circuit turns off. This is called the "Flip-Flop" effect. If the finger is kept on the pads, the circuit will turn on-off-on-off at a rate of about once per second. This is shown in Circuits B.

3. Touch one set of pads to turn the circuit on and another set of pads to turn the circuit off.
This is shown in Circuits C.

CIRCUITS A
Here are a number of circuits that turn on a device when the touch-pad is touched.
The circuit above is the simplest Touch Switch. It is called a "super-Alpha pair" and is actually identical to a single transistor with a very high gain.
Putting a finger on the touch pads turns the top transistor ON and this transistor turns on the bottom transistor. When the finger is removed, the circuit consumes less than a microamp.
The 555 can be used to create a Touch Switch. The only problem with this is the 555 consumes about 8mA, at all times when the supply is connected. The circuit above turns on the LED when the finger is applied and pin t becomes "open circuit." This allows the 10u to charge via the 100k resistor and when pin 6 detects a HIGH, the LED turns off. The finger should be removed before this occurs. See below for an ON-OFF touch switch using a 555.The Touch Switch circuit above is a very complex design to do a simple task. It is also a very poor design as the biasing (turn-on) for the output transistor is via a resistor and the output transistor is turned off by taking the biasing current to the 0v rail. This is a wasteful design if the circuit is to be powered by a battery.

The circuit above has a signal "sitting" on the TOUCH PLATE via the oscillator made up of a Schmitt trigger between pins 1 and 2. The operates as a square-wave oscillator at approximately 150 kHz. The oscillator's output gets ac-coupled to R₂ that sets the drive level and hence, the sensitivity for the touch pad. Applying negative excursions of several volts of a square-wave signal to its gate repetitively drive N-channel JFET Q₁ from conduction into cutoff. An approximation of the square wave swinging from 0 to 12v appears at Q₁'s drain. A peak detector circuit formed by D₁; R₇ and C₄ provides sufficient dc voltage to force IC_1B's output to a logic low.
However, if someone touches the touch pad, any added capacitance to ground reduces the ac drive at the FET's gate, and Q₁ continuously conducts. The square-wave voltage applied to D₁ decreases. The voltage on C₄ drops below the logic threshold, and IC_1B's output goes high. You can adjust R₂ to set sensitivity and compensate for device-to-device variations in the FET's pinch-off voltage.

The following circuit does not work. It uses a CD 4001
The TRUTH TABLE for a NOR gate is:

NOR GATE
INPUT	OUTPUT
0 0	1
1 0	0
0 1	0
1 1	0

We can see from the Truth Table that the output of a gate only changes when both inputs are LOW. For the top gate, pin 1 never goes low so this type of gate will not work.

Try a NAND gate:The circuit above does not work. By checking the Truth Table, we see the gates are correct:

NAND GATE
INPUT	OUTPUT
0 0	1
1 0	1
0 1	1
1 1	0

But the circuit does not turn off. The reason is the 4u7 is not charge or discharged by any component in the circuit. When the circuit is first turned on, the electrolytic is uncharged and pin 5 is effectively connected to pin 3. If output pin is HIGH, pins 5&6 will be HIGH and pin 4 will be LOW. This will make pin 3 HIGH. Both the Touch Wires will be HIGH and touching them will not change the state of the circuit.
We need a component to allow the 4u7 to charge and make pins 5&6 LOW.
The next diagram does this:The 100k "safety resistors" have been removed as they do not play a part in the operation of the circuit and the touch wires have been connected to the circuit to have the greatest effect.

CIRCUITS B
The following circuits show a "flip-Flop" effect. The circuit changes state, each time the touch pads are touched.

If a finger is kept on the touch plates in any of the toggle circuits above, the circuit will oscillate ON, OFF, ON, OFF at a low frequency. The frequency of 3 sec, 0.5 sec has been identified in the top circuit. An improvement to the Toggle Touch Switch above, to keep the charge on the 100n, is to use a second gate:A touch switch can be made with 2 gates from a 4049UB IC, as shown in the following circuit. It has proven to be reliable at 6v and 12v. The design has the advantage that the output does not cycle if a finger is kept on the Touch Pads.
CIRCUITS C
These circuits have two touch plates. One touch plate turns the circuit on and the other plate turns the circuit off.


Mouse- over: to see circuit work

The TOUCH-PADS deliver current from the power rail to the input of the circuit, via a moist finger. The finger acts as a very high vale resistor. Note the 4M7 feedback resistor that keeps the circuit on when the finger is removed.
The circuit above is available from Talking Electronics as a kit. The kit is called TOUCH SWITCH:

TOUCH SWITCH USING A CD 4011 IC

A TOUCH SWITCH using a CD 4011 is shown in the diagram above.

A simpler version is shown below:
When the circuit is first turned on, the two gates will "race" and the fastest gate will create a HIGH output. It cannot be determined if the LED will light when the circuit is first turned on. By adding the 100p (shown in red) to the position shown on the circuit, one input of the gate will start with a LOW and this will make pin 4 HIGH. The top gate will have HIGH on both inputs and the output will be LOW. This will turn on the LED. It is not know why the previous circuit used all 4 gates of the 4011. The circuit was taken from a kit manufactured by a non-electronics person and he did not investigate the possibility of simplification.
Since the output of a CD 4011 is not capable of sinking or sourcing a high current, you can buffer the output of the gate with the third gate in the chip and wire it as an inverter.

ON-OFF TOUCH SWITCH USING A 555 IC

For those who like the rugged 555, we have included a 555 ON-OFF touch switch.

TOUCH PADS
A touch Pad can be obtained from many different sources. The photos below show a touch pad obtained from a toy. Some of the very light touch buttons consist of a small carbon block mounted in silicon rubber and when the button is pressed, the carbon block touches the pad and reduces the resistance between the two interleaved tracks.

3 TOUCH PADS

<Close-up of the touch pad

This part of the circuit board can be cut away and used as a touch pad for the circuits in this discussion. The pads are already protected from corrosion and form a very good design for detecting a finger.
The important feature of the pad is the number of interleaving fingers as this is equivalent to a pair of lines about 12cm long and when a finger is applied, the resistance between the lines drops to between 150k and 850k, depending on the pressure and moisture in the finger.

HIGH IMPEDANCE CIRCUIT
We have already said a touch pad is a high impedance device (circuit), but what does this mean and how does it work?
We are going to explain why it must be a high impedance circuit.
Below we have four different touch pad circuits. The supply voltage does not matter, however we have shown it as 6v. The main purpose of a touch pad is to reduce the voltage on the "output." Generally this must be15% - 25% of rail voltage to trigger the circuit.

If we take the first circuit "A" and place a finger on the touch pad, the circuit becomes equivalent to two resistors in series. These two resistors form a voltage divider and the voltage on the output is in proportion to the value of the resistances. We will assume the resistance of the finger is 1M to make the discussion simple. The 5M resistor is not a standard value but s also used to make the discussion easy to understand. In the diagrams below, the output of the
touch pad is 6v when nothing is touching the pad. When a finger touches the pad, the voltage drops to 1v. Without using mathematics, we can see the 5Meg resistor is in series with the 1Meg finger, making a total of 6Meg. This means 1v appears across each 1Meg and thus the output is 1v.
If we apply the same finger to circuit "B," the output voltage will drop to 3v. This voltage may not be low enough to trigger the circuit connected to the touch pads.
If we apply the same finger to circuit "C," the output voltage will drop to 5.4v. This voltage will not be low enough to trigger any circuit connected to the touch pads. Let's look at how this voltage is created. The two resistors are 100k and 1M in series. If we convert the 1M into ten 100k resistors, each resistor will have the same voltage across it. There are 11 x 100k resistors and this means very close to 0.6v will appear across each resistor. That is why the output voltage will be about 5.4v when the finger touches the pad.

From this we can see the "pull up" resistor must be as high as possible so the effect of a finger will reduce the output voltage of the pad to a low value.
There is one other important factor to remember.
The output of a touch pad must be connected to a high impedance input. The diagram below shows the gates and a "super-alpha" transistor. These all have a high impedance input.

Why do we need a high impedance input?
Suppose the circuit we are connecting to the touch pad has a low impedance. It will be equivalent to placing your finger on the touch pads. The output will go low and your finger will not be able to create a HIGH-LOW voltage change.
The input impedance of a gate can be considered to be very high (greater than 10M). When the "super-alpha" pair is connected to the touch switch, the voltage on the "output" of the touch pad will not rise above 1.3v. This is due to the base-emitter junctions of the two transistors.
The output of the super-alpha pair will be low. When a finger is placed on the touch pads, the output of the super-alpha pair will rise.
An alternate circuit for connecting touch pads to a super-alpha pair is shown below:

LATCH CIRCUIT
Here are two latch circuits using transistors. The first operates exactly the same as the 4-transistor Touch Switch above. It can be used with a touch pad. It's another "Building Block" to add to your collection. The second circuit operates in the same way. When the circuit is first turned on, both transistors are not conducting. As the input voltage increases to 0.65v, the BC 547 transistor turns on and this turns on the BC 557. The BC 557 is connected to the base of the BC 547 and it takes over from the input voltage. The two transistors turn each other on until both are fully turned on. The supply must the turned off to reset the circuit.

Here is a Touch Switch circuit from a magazine:

Why use half a chip and a FET to do the same as our 74c14 circuit above?
That's why you need to know how to design circuits, so you don't over-design.
See our "Spot The Mistake" article for more over-designed and incorrectly designed circuits. You learn more from other people's mistakes than anything else.

USING A TOUCH SWITCH IN A PROJECT

1. DOORKNOB ALARM
The 74C14 (40106) is a hex Schmitt trigger IC with 6 gates that can be used for 6 different building blocks. Even though it has a "74" marking, it can be placed in a circuit with a voltage as high as 15v - all the other 74 series require a maximum of 5v for the supply. (More data on the 74C14 can be found in Chip Data eBook.)

In the following circuit, the gates are used to detect the touch of a door knob and produce an output that goes HIGH for approx 1 minute.

The output of the above circuit can be taken to an alarm. Open the reed switch contacts and connect the reed switch to the output of the Door-knob alarm.

A suitable alarm can be found in the $2.00 "Junk Shops" for about $2.00 These consist of a piezo diaphragm and a driver circuit consisting of a transistor and COB (Chip On Board) to produce a very loud wailing sound. Some of the devices have an inductor to increase the voltage to about 60v to 80v to produce an output of about 90dB. The device we bought had a transformer to drive the piezo to 80v.
The photo shows the device and magnet. The magnet holds a reed switch closed and when the two items are parted, the reed switch opens and sounds the alarm.

The reed switch can be seen in the photo below. It is an uncovered reed switch consisting of two soft-iron strips that overlap slightly in the centre. When a bar magnet is brought near, the two strips become magnetised with each forming a north at the top and south pole at the bottom. This means the top strip has a south pole at its bottom and the lower strip has a north pole at its top. Since unlike poles attract, the two strips will touch each other when a bar magnet is present.

When a magnetic object comes in the vicinity of a magnet, it becomes temporarily magnetised with North and South poles. This is shown in the diagram. This is how the two strips of the reed switch close and "stick together" when the magnet is near.

The magnetic field of the bar magnet causes the two
parts of the reed switch to become "magnetic."

The side of the alarm showing Chime (Doorbell), Off
and Alarm. See below for a link to these sounds.

The underside of the alarm showing the COB module and the 4 pins from the transformer that drives the piezo diaphragm. To hear the "DoorBell" sound and "Alarm" sound, click HERE. or here: SOUND

Open the reed switch so the Door-Knob circuit can operate the alarm.

2. TOUCH MOTOR CONTROL
- by L. W. Brown, Burwood, Victoria, Australia.

The following circuit is suitable for operating a12v motor such as on a display in a shop window. The 50mm x 50mm touch plate can be stuck to the inside of the glass and anyone placing their finger near the touch plate (on the outside of the window) will prevent the signal entering the charge pump section of the circuit and keeping the 10n charged.
The circuit will take a few seconds before the 10n is discharged via the 10M and the motor will operate.

3. TOUCH-ON TOUCH-OFF
This circuit is an extension of the Door-knob Alarm presented above. It turns on an output when the Touch-Plate is touched very briefly and turns off the output when the plate is touched for a slightly longer period of time.

TOUCH-ON TOUCH-OFF SWITCH

This article has covered more than 10 building blocks and shown how to adapt a low-cost item in a junk shop to a circuit you have already designed.
It has also covered the concept of a HIGH IMPEDANCE CIRCUIT and FEEDBACK to keep a circuit stable in either of its two states.
Even if you think you will never need a TOUCH SWITCH in a future project, the building blocks we have covered can be used in lots of different circuits and if you build them, you will have a much-better understanding of how they work.

USB Sound Card with PCM2702

2009-06-06T20:40:00.000-07:00

Make a sound card is no more a complex issue. If you use great IC PCM2702 from BURR BROWN / Texas Instruments you can create a fully functional USB sound card. This sound card can be powered from USB port and has one stereo output. You don�t need to install any driver for Windows XP and Vista, because they are already inside. This is really plug and play.

Few months ago I have seen USB sound card called Alien DAC. The construction on the project web page inspired me to build this thing also.

Description

The core of this construction is 16-Bit Stereo Digital-To-Analog Convertor with USB interface PCM2702.

PCM2702 needs only few additional parts to work. The schematic is not complex. Sound card can be powered directly from USB port (jumper W1) or from external power supply (jumper W3). PCM2702 needs two power supply 3.3V (3V-3.6V) and 5V (4.5V-5.5V). I used fixed output voltage LDO TPS76733Q for 3.3V (IO2) and adjustable output voltage LDO TPS76701Q for 5V (IO3). Both LDO are produced by TI, I used this because I had it in my drawer. Any similar LDO can be used. Output voltage of IO3 should be set to little bit lower than input voltage to allow LDO good stabilization, in my case output voltage is set to 4.8V. Output voltage can be set by adjustable resistor R33. In case of low power supply, IO3 can be shorted by jumper W3. LED D3 signalizes power on.

Assembled top side

Small ferrite beads are placed before all power pins of PCM2702 and in Vbus and GND of USB. These small beads reduce high frequency hum. I had a problem find this small SMD ferrite beads in local stores but finally I acquire few of them from old hard drive. They are not absolutely necessary, you can use zero ohm resistors instead of them.

Low-pass filter is placed in output signal path to reduce sampling frequency. An OPA2353UA dual op amp is configured as a stereo 2nd-order low-pass filter. Led diode D1 is illuminated when PCM2702 plays audio data received from the USB bus. Led diode D2 is illuminated when USB bus suspends audio data transmission to the PCM2702.

Schematic

Schematic of sound card with PCM2702

PCB

PCB assembly diagram
PCB - Download PCB in [EPS format] or [PDF format]

Bottom side of PCB (single side PCB, made by standard etching method)

Assembled bottom side

Conclusion

This circuit works very well. I only shorted crystal during soldering so the circuit didn�t work, but after removing the short the sound card started to work. I have tested in Windows 2000, XP and Vista. It works in all mentioned systems. Drivers are present in operation system so the sound card is ready in few seconds after you connect it.

During writing this article I have found that PCM2702 is now not recommended for new design, but TI offer even better solution. PCM2704, PCM2705 have same functionality as PCM2702, but they include output filter. They are able to drive directly headphones. Volume and Mute can be controlled through SPI bus in PCM2705 or with pushbuttons in case of PCM2704. PCM2704 and PCM2705 are in TSSOP28 package. PCM2706 is similar to PCM2704 and PCM2707 to PCM2705 but in addition they have I2S bus. PCM2706 and PCM2707 are in TQFP32 package. I recommend using these new chips for new design (look at the TI web page).

Links

PCM2702 Texas Instrument
PCM2702 Evaluation Board
Alien DAC

source by : ELECTRONIC LAB

High Power LED mood Lamp

2009-06-06T19:26:00.000-07:00

Introduction

In this page we will introduce a great project designed by Toon Beerten. His project named "DIY Led Mood Lamp" can become a very interesting add-on for your room that's absolutely sure it will impress everyone. As you can see on the photos, we talk about a color fading lamp, that looks amazing!

The purpose of this page is to try to give some hints building it successful. This high power led mood light is based on PIC16F628 and the ability of this mcu to produce PWM pulses. Varying pulse width we can produce millions of color combinations using only the three basic colors. So only one RGB (Red-Green-Blue) led is capable producing a rainbow of fading colors.
With the help of four switches we can handle all functions of the lamp. We can choose fading or jumping between colors, we can select a rainbow style or a random color changing behavior, we can choose slow or fast changing of colors and we can pause on a desired color.

Finally we will make some power dissipation measurements to help us select an appropriate power supply unit.

Housing for best color diffuse

You can use your imagination to find a housing that will be able to diffuse colors uniformly. Color difussion is necessary to achieve best results. In original design the author used the 45cm IKEA Mylonit lamp. That's a great housing for your lamp. Instead you can use the smaller 31cm IKEA Mylonit lamp with the same amazing results. That's the lamp we used in our construction.
In our research we found other lamps (ex. sphere shape) that are ideal for housing your big led.

High Power LED

The led used is a high power 3W RGB LED. It can be found on ebay at LEDSEE-electronics. You can also check ebay for other high power RGB leds. It will do the jod the same way. Details of this brilliant led shown below.

3W high power RGB LED

Note: Minus on the bottom right pin is common anode (positive voltage)

Light Angle of the LED 140 degree°
Nominal current B,G,R 350mA

Forward voltage:
Red Typ 2,2V
Green Typ 3,55V
Blue Typ 3,55V

Wavelength of the LEDs:
Red Typ 625nm
Green Typ 530nm
Blue Typ 470nm

Luminous Intensity:
RED Typ 32lm
Green Typ 35lm
Blue Typ 10lm

LED type: Common Anode

Schematic

The schematic used is shown in the next image. It's as simple as it shows. Take care on the correct transistor mount and correct polarity of power source.

Schematic (click image for higher resolution)

BC337 Pin out

Parts List

Here is a list of the components i used for making the led mood lamp.

- 3 x NPN transistors capable of driving 500 mA, for example the BC337
- one PIC 16F628(A) and a programmer
- a small perforated circuit board
- 7 x 10K resistors (1/4W)
- some 1 watt resistors (4,7, 10 and 15 Ohm) and a DIP switch
- a power supply (5 volts, 500 mA)
- Ikea Mylonit lamp or other housing
- silicon paste from your local DIY shop (if you want to use a heatsink)
- one z-power 3 watt rgb led
- a little heatsink and some cooling paste (if you want to use a heatsink)

Circuit board

On the next image you can see the circuit arranged on a perforated board.
Programming The PIC 16F628 Microprocessor

Programming the PIC16F628 can be achieved using this very simple pic programmer and a program called ic-prog. Just use your programmer and upload the .hex file on your PIC. For successful results you should pay attention on the fuse bits. You should enter the correct fuses as noted on the following table.

Fuses

IntRC I/O = Enabled
PWRT = Enabled
BODEN = Enabled
MCLR = Disabled
Rest of fuses = Disabled

DIP Switches functions

SW1 - makes you choose between G->GB->B->BR->R->RG-->>G effect and random color change effect
SW2 - makes you choose between fading and jumping from one color to another
SW3 - makes you choose between slow or fast
SW4 - pauses at the current color displayed

Mounting

A good way to mount the circuit board is to use a hot glue gun to "mold" the circuit underneath the lamp housing. There is plenty of space there for your board. At the next photos you can see the circuit board mounted on the small 31cm IKEA Mylonit Lamp.

The glue is still hot. Temperature of glue didn't damage the PIC or other parts.

The glue is now cold and you can easily access the dip switches. Lamp is working!

A view from top of the lamp.

Power dissipation

Finally we have done some current measurements to measure power dissipation. It's clear that current changes as colors are changing. As you can see the max current needed is 232mA. You should keep in mind that this depends on the led you have and the power resistors you choose.

As a conclusion a power supply rated at 5V/500mA will be sufficient.

Touch Switch ON-OFF

2009-06-03T02:37:00.000-07:00

The modern mechanic switches are improved concerning of old technology. We need however many times to replacement some old switch or to check currents bigger than the durability of certain switches or simple we need something with modern appearance. For he and different reasons is essential the up circuit. He is simple in the manufacture and the materials that use they exist everywhere. This based in the known 555, which drives a relay of which the contacts play the role of switch. The metal surfaces can have what form we want, but it should they are clean and near in the circuit. In order to it changes situation it suffices touch soft somebody from the two plates. Plate JF1 in order to the contacts of RL1 close [ON] or plate JF2 in order to the contacts of RL1 open [OFF]. The current that RL1 will check depended from his contacts. The Led D2 turns on when the switch they are in place ON and the contacts of RL1 closed.

Part List

R1-2=3.3M 1/4W 5%	D1=1N4148	RL1=12V Relay [Your choise ]
R3=10K 1/4W 5%	D2= Red LED 3 or 5mm.	JF1-2=Metal Plate
R4=1K 1/4W 5%	Q1=BC547
C1=10nF 63V MKT 5%	IC1=555

electronic smoke detector circuit that can be used as a fire alarm

2009-06-03T02:23:00.000-07:00

This circuit uses a very simple approach to detecting smoke in the air. Quite simply, it uses a bulb as a light source, and an LDR (Light Dependent Resistor) as a light detector. As fire smoke comes between the bulb and LDR, the resistance of the LDR changes, which in turn trigger an alarm.

This probably isn't an ideal approach given that ambient light levels are likely to cause false alarms, however it is an interesting experiment. Just please don't set any fires while experimenting. And please don't rely on it as a replacement for a real fire alarm device.

Police Siren

2009-05-27T23:15:00.000-07:00

Click here for Circuit Diagram.This circuit produces a sound similar to the police siren. It makes use of two 555 timer ICs used as astable multivibrators. The frequency is controlled by the pin 5 of the IC. The first IC (left) is wired to work around 1Hz. The 47uF capacitor is charged and discharged periodically and the voltage across it gradually increases and decreases periodically. This varying voltage modulates the frequency of the 2nd IC. This process repeats and what you hear is the sound remarkably similar to the police siren.

Two presets VR1 and VR2 are provided to vary the siren period of repetition and the tone of the siren. By varying VR1 you can set how fast the siren changes from high freq. to low freq. VR2 sets the siren frequency. Adjust VR1 and VR2 to suit your taste.

Melody generator for greeting cards

2009-05-27T23:08:00.000-07:00

Click here for Circuit Diagram.This tiny circuit comprising of a single 3 terminal IC UM66 can be built small enough to be placed inside a greeting card and operated off a single 3V flat button cell.

There is not much to the circuit. The UM66 is connected to its supply and its output fed to a transistor for amplification. You can either use a 4ohm speaker or a " flat" piezoelectric tweeter like the one found in alarm wrist watches.
If you use the piezo, then it can be connected directly between the output pin 1 and ground pin 3 without the transistor.
The UM66 looks like a transistor with 3 terminals. It is a complete miniature tone generator with a ROM of 64 notes, oscillator and a preamplifier. When it first came into market, it was programmed for the "Jingle bells" tune. Now they come with a wide variety of different tunes.

Brakelight Flasher

2009-05-27T23:02:00.000-07:00

This is basically a flasher circuit modified to turn on and off a bulb instead of a LED. It uses a 555 timer IC working as an astable multivibrator. The flashing rate can be varied from very fast to a maximum of once in 1.5 sec by varying the preset VR1.
The ON time of the circuit is given by:
TON= 0.69xC1x(R1 + VR1) second

and the OFF time is:
TOFF= 0.69xC1xVR1 second

You can increase the value of C1 to 100uF to get a slower flashing rate of upto once in 10 sec.

4 in 1 Burglar Alarm

2009-05-27T22:56:00.000-07:00

I n this circuit, the alarm will be switched on under the following four different conditions: 1. When light falls on LDR1 (at the entry to the premises). 2. When light falling on LDR2 is obstructed. 3. When door switches are opened or a wire is broken. 4. When a handle is touched. The light dependent resistor LDR1 should be placed in darkness near the door lock or handle etc. If an intruder flashes his torch, its light will fall on LDR1, reducing the voltage drop across it and so also the voltage applied to trigger 1 (pin 6) of IC1.

Thus transistor T2 will get forward biased and relay RL1 energise and operate the alarm. Sensitivity of LDR1 can be adjusted by varying preset VR1. LDR2 may be placed on one side of a corridor such that the beam of light from a light source always falls on it. When an intruder passes through the corridor, his shadow falls on LDR2. As a result voltage drop across LDR2 increases and pin 8 of IC1 goes low while output pin 9 of IC1 goes high. Transistor T2 gets switched on and the relay operates to set the alarm. The sensitivity of LDR2 can be adjusted by varying potentiometer VR2. A long but very thin wire may be connected between the points A and B or C and D across a window or a door. This long wire may even be used to lock or tie something.

If anyone cuts or breaks this wire, the alarm will be switched on as pin 8 or 6 will go low. In place of the wire between points A and B or C and D door switches can be connected. These switches should be fixed on the door in such a way that when the door is closed the switch gets closed and when the door is open the switch remains open. If the switches or wire, are not used between these points, the points should be shorted. With the help of a wire, connect the touch point (P) with the handle of a door or some other suitable object made of conducting material. When one touches this handle or the other connected object, pin 6 of IC1 goes �low�. So the alarm and the relay gets switched on. Remember that the object connected to this touch point should be well insulated from ground. For good touch action, potentiometer VR3 should be properly adjusted. If potentiometer VR3 tapping is held more towards ground, the alarm will get switched on even without touching. In such a situation, the tapping should be raised.

But the tapping point should not be raised too much as the touch action would then vanish. When you vary potentiometer VR1, re-adjust the sensitivity of the touch point with the help of potentiometer VR3 properly. If the alarm has a voltage rating of other than 6V (more than 6V), or if it draws a high current (more than 150 mA), connect it through the relay points as shown by the dotted lines. As a burglar alarm, battery backup is necessary for this circuit. Note: Electric sparking in the vicinity of this circuit may cause false triggering of the circuit. To avoid this adjust potentiometer VR3 properly.

ေတြ႔ခ်င္ေသာ blogger ၁၀ ေယာက္ (Tag post)

2009-05-19T20:30:00.000-07:00

ကြ်န္ေတာ္ ေတြ႔ခ်င္ေသာ blogger ၁၀ ေယာက္ ကေတာ့

၁။မႀကီး မသဒၶါ (ကြ်န္ေတာ့္ ရဲ႕ ဘေလာ့ဂ္ ေလာကမွာ ပထမဦးဆံုးေသာ ဆရာပါ။)
၂။ကိုေကာင္းကင္ကို (ကြ်န္ေတာ္ ေလးစားရေသာ ကဗ်ာဆရာ)
၃။ကိုမိုးသီဇြန္ (ကြ်န္ေတာ္ ေလးစားရေသာ ဘေလာ့ဂ္)
၄။ကိုနစ္ေနမန္း (ကြ်န္ေတာ္ ေလးစားရေသာ ဘေလာ့ဂ္)
၅။ကိုအိုးေ၀ေအာင္ (ေက်ာင္းတုန္းက မသိေပမဲ့ ဘေလာ့ဂ္ ေလာကက်မွ ခင္မင္ခဲ့သူ)

သူတို႔ေတြကေတာ့ ကြ်န္ေတာ္ နဲ႔ တစ္ႏိုင္ငံတည္းမွာ အတူတူ အလုပ္လုပ္၊ ေက်ာင္းတတ္ၿပီး ဒုကၡေတြ ကို စုေပါင္းခံစားေနၾကတဲ့ ကြ်န္ေတာ္ ရဲ႕ ညီအစ္ကို ေမာင္ႏွမေတြပါ။... တခ်ဳိ႕ က ကြ်န္ေတာ္ နဲ႔ နီးရက္နဲ႔ ေ၀းေနရတဲ့ ကြ်န္ေတာ္ အေတြ႔ခ်င္ဆံုး ထဲက လူ ၁၀ ေယာက္ထဲက စာရင္း၀င္ေတြပါ...

၆။ငြန္းငယ္မိုး သူကေတာ့ ကြ်န္ေတာ္ ကို ညီအစ္ကို လိုခင္တယ္.. စာအေရးအသားေတြလဲ ေကာင္းတယ္... စိတ္႐ွည္တယ္... ဇြဲမေလွ်ာ့တတ္ဘူး ထင္တယ္..
၇။Co2zenith သူကေတာ့ ကြ်န္ေတာ္ ကို အစ္ကို ဆရာလို႔ အၿမဲေခၚတယ္.. ကြ်န္ေတာ္ က ဆရာ မဟုတ္ပါဘူး... အခုမွ Blogger ေတြ အတြက္ HTML code ေတြကို ေလ့လာ သင္ယူေနဆဲပါပဲ... ကြ်န္ေတာ္က သူ႔ကို ညီညီ ဆရာလို႔ ျပန္ေခၚတယ္ေလ... သူနဲ႔ ခင္မင္ရတာ ေပ်ာ္စရာပါ... သူက မဟုတ္မခံ စိတ္႐ွိပံုရတယ္... ၿပီးေတာ့ စိတ္ဆတ္တယ္ ထင္တယ္..
၈။ၿဖိဳးေ၀တိုး သူ႔ကိုေတာ့ ကြ်န္ေတာ္ ေသခ်ာ မသိဘူး... သူ႔ကို ကြ်န္ေတာ္ စိတ္မွန္းနဲ႔ သိတယ္... သူလဲ နည္းပညာေတြ ကို ေတာ္ေတာ္ေလး သိပံုရတယ္... ဘေလာ့ဂ္ေတြမွာ သူ႔လက္ရာေတြ မ်ားလို႔ သူ႔ကို ကြ်န္ေတာ္ ျမင္ဘူးခ်င္တယ္... ေတြ႔ခ်င္တယ္.. သူက ကြ်န္ေတာ္ ေနတဲ့ ေနရာေလးနဲ႔ လွမ္းေနေတာ့ ေတာ္႐ံုေတာ့ ေတြ႔ႏိုင္မယ္ မထင္ဘူး.. အသက္ငယ္ေပမဲ့ ကဗ်ာေတြ ေရးတာေကာင္းတယ္.. ေလးစားမိပါတယ္..
၉။ညေလး သူကေတာ့ အခ်က္အျပဳတ္ ကိုေတာ္ေတာ္ေလး ၀ါသနာပါပံုရတယ္.. သူ႔ဘေလာ့ဂ္မွာ သြားၾကည့္လိုက္ရင္ အခ်က္အျပဳတ္နည္းေတြ မ်ားတယ္... ကဗ်ာေတြ စာေတြ ေဆာင္းပါးေတြ ေရးတာလဲ ေကာင္းတယ္... Gtalk မွာ chat ေျပာၾကရင္လဲ သူ႔ဘက္က ခိခိ ဆိုၿပီး အရင္ စ႐ိုက္တာမ်ားတယ္... သူ အဲဒီလို ႐ိုက္မွ ပဲ ကြ်န္ေတာ္ ကေတာ့ ဒီဘက္မွာ ၿပံဳးေနမိတယ္... သူက ေပ်ာ္ေပ်ာ္ေနတတ္ပံုရတယ္.. အဲဒါေၾကာင့္ ျမင္ဘူးေတြ႔ဘူးခ်င္တယ္..
၁၀။သဇင္ဏီ သူကေတာ့ ရယ္စရာ ဟာသေတြ ေပါက္ကရ၆၀ ေတြ ေရးတယ္... တစ္ခါတစ္ခါ စိတ္ညစ္စရာေတြ ႀကံဳေနရတဲ့ အခ်ိန္ေတြမွာ သူ႔ဘေလာ့ဂ္ဆီကို ေရာက္ျဖစ္တယ္.. သူေရးထားတဲ့ စာေတြကို ဖတ္ၿပီး ရယ္စရာေတြနဲ႔ ဘ၀ အေမာေတြကို ေျပေစတယ္.... သူက ခင္မင္တတ္တယ္... လူေတြကို သနားတတ္ပံုရတယ္.. ဒါေၾကာင့္ သူ႔ကို ေတြ႔ဘူးခ်င္တယ္...

က်န္တဲ့ ဘေလာ့ဂၢါေတြေရာ မေတြ႔ခ်င္ဘူးလားဆိုေတာ့ အရမ္းေတြ႔ခ်င္ပါတယ္...။ ကြ်န္ေတာ္တို႔ မေလးေျမမွာ ေရးေနၾကတဲ့ ဘေလာ့ဂၢါေတြ အကုန္လံုးကိုေပါ့...

ကြ်န္ေတာ္တို႔ေတြ တစ္ခ်ိန္ခ်ိန္မွာ အားလံုးစံုၿပီး ေတြ႔ၾကဖို႔ မလြယ္သလို... ေတြ႔ျဖစ္ေအာင္ ေတြ႔ၾကရေအာင္လားဗ်ာ... ကြ်န္ေတာ္တို႔ ဘေလာ့ဂၢါေတြ စုၿပီး ဆံုၿပီး ေပ်ာ္ေပ်ာ္ပါးပါးႀကီး စကားေတြ တ၀ႀကီး ေျပာၾကရေအာင္လားဗ်ာ... ဟိုတစ္ေလာက သႀကၤန္မွာ ကိုလတ္ႀကီး ေရးထားသလို အဲဒီလိုမ်ားဆံုျဖစ္ခဲ့ၾကမယ္ ဆိုရင္ ကြ်န္ေတာ္တို႔ေတြ ဘယ္ေလာက္ေတာင္ ေပ်ာ္စရာ ေကာင္းလိုက္မလဲေနာ္...

အားလံုးေပ်ာ္႐ႊင္ႏိုင္ပါေစဗ်ာ....

DOORKNOB ALARM

2009-05-08T01:23:00.000-07:00

Many companies offer simple alarm devices for personal use in bedrooms or hotel rooms. A metal chain attached to a box holding the electronics is placed around the inside doorknob of a wood door. Anyone grabbing the knob from the outside is detected by the electrical capacitance change that occurs from the human hand contact between the knob and the box. Almost all of the commercial devices sold use a more expensive and power consuming radio frequency circuit approach to detect the capacitance change. But, a very inexpensive and micro power technique can also work. This circuit schematic should dramatically reduce the cost of the device and allows it to operate for many years from one set of batteries.

Simple Home Alarm System

2009-05-08T00:54:00.000-07:00

This Home Alarm System is simple, secure, fast and cheap. It's only few components with maximum security with Rolling Code TX and Shock Sensor with variable sensitivity. The alarm module can be assembled in only 2 hours and it don't need manual preset.

Home Alarm System with this characteristics is the most cheap system and the total cost could be reduced using a normal external sounder (escl. AG8).GSM module will be add in the future for a remote control.

The blue led connected to the pin RA3 of micro controller is used like a memory to know if the home alarm system has been activated by an event and its reset after a reactivation. The red led connected to the power supply before the 1N5406 diode is used to check the power supply connection. Of course the other 3 micro led red near the relays are used to check the output state.

Enhanced 4-Digit Alarm Keypad

2009-05-08T00:30:00.000-07:00

Pressing a single key on the keypad - will energize the relay. Entering a four-digit code of your choice - will de-energize the relay. The circuit was designed to control the Modular Burglar Alarm System - but it will have other applications. If you require added security - A Five-Digit Version - of the circuit is also available.

Schematic Diagram

Notes
The Keypad must be the kind with one common terminal - and a separate connection for each key. On a 12-key pad - look for 13 terminals. The matrix type with 7 or 8 terminals will NOT do. On the Support Page you'll find details of how to Make Your Own Keypad.

The relay is energized by pressing a single key. Choose the key you want to use - and connect it to terminal "E". Choose the four keys you want to use for your security code - and connect them to "A B C & D". Wire the common lead to R1- and all the remaining keys to "F".

When you press "E" the relay energizes - and the 12-volt output moves from the "off" to the "set" terminal. The green LED also lights. It provides a visual indication that the alarm is set.

When you press keys "A B C & D" in the right order - the relay de-energizes - and the 12-volt output returns to the "off" terminal. The green LED is also extinguished - to indicate that the alarm is switched off.

The remaining keys - those not wired to "A B C D & E" - are connected to "F". Whenever one of these "Wrong" keys is pressed - the attempted code entry fails - and the code entry sequence is reset.

The same thing happens if "C" or "D" is pressed out of sequence. If "C" is pressed before "B" - or "D" is pressed before "C" - the attempted code entry will fail. And the code entry sequence will reset.

With a 12-key pad - over 10 000 different codes are available. If you need a more secure code - you could simply use a bigger keypad with more "Wrong" keys wired to "F". A 16-key pad gives over 40 000 different codes. If you make a mistake while entering the code - simply start again.

The Support Material for this circuit includes a step-by-step guide to the construction of the circuit board - a parts list - a detailed circuit description - and more.

Veroboard Layout

Low Voltage 120vac Power Line Alarm

2009-05-08T00:25:00.000-07:00

This circuit will turn on a beeper when the line voltage drops below 100 volt AC.

Click on Drawing Below to view PDF version of Schematic

This circuit turns on a beeper whenever the inside temperature of a freezer is greater then zero degrees Centigrade. The circuit draws only a few mic

2009-05-08T00:21:00.000-07:00

This circuit turns on a beeper whenever the inside temperature of a freezer is greater then zero degrees Centigrade. The circuit draws only a few microamps from a 9 volt battery. It uses a glass bead thermistor accurate to 1 degree C.

Fake Car Alarm Light

2009-05-08T00:14:00.000-07:00

Whenever the car's ignition is turned off, this circuit activates a flashing LED, which can be positioned to appear as an active alarm system.

ELECTRIC FIELD DISTURBANCE MONITOR

2009-05-08T00:05:00.001-07:00

This schematic is the power supply and front-end sections of the field monitor that is discussed in more detail at Electric Field Disturbance Monitor. (this link is off-site) The system can detect human and animal motion by the electric fields they disturb.

Radio Remote Control using DTMF Circuit

2009-03-04T19:33:00.000-08:00

Here is a circuit of a remote control unit which makes use of the radio frequency signals to control various electrical appliances. This remote control unit has 4 channels which can be easily extended to 12. This circuit differs from similar circuits in view of its simplicity and a totally different concept of generating the control signals. Usually remote control circuits make use of infrared light to transmit control signals. Their use is thus limited to a very confined area and line-of-sight. However, this circuit makes use of radio frequency to transmit the control signals and hence it can be used for control from almost anywhere in the house. Here we make use of DTMF (dual-tone multi frequency) signals (used in telephones to dial the digits) as the control codes. The DTMF tones are used for frequency modulation of the carrier. At the receiver unit, these frequency modulated signals are intercepted to obtain DTMF tones at the speaker terminals. This DTMF signal is connected to a DTMF-to-BCD converter whose BCD output is used to switch-on and switch-off various electrical applicances (4 in this case). The remote control transmitter consists of DTMF generator and an FM transmitter circuit. For generating the DTMF frequencies, a dedicated IC UM91214B (which is used as a dialler IC in telephone instruments) is used here. This IC requires 3 volts for its operation. This is provided by a simple zener diode voltage regulator which converts 9 volts into 3 volts for use by this IC. For its time base, it requires a quartz crystal of 3.58 MHz which is easily available from electronic component shops.

Pins 1 and 2 are used as chip select and DTMF mode select pins respectively. When the row and column pins (12 and 15) are shorted to each other, DTMF tones corresponding to digit 1 are output from its pin 7. Similarly, pins 13, 16 and 17 are additionally required to dial digits 2, 4 and 8. Rest of the pins of this IC may be left as they are. The output of IC1 is given to the input of this transmitter circuit which effectively frequency modulates the carrier and transmits it in the air. The carrier frequency is determined by coil L1 and trimmer capacitor VC1 (which may be adjusted for around 100MHz operation). An antenna of 10 to 15 cms (4 to 6 inches) length will be sufficient to provide adequate range. The antenna is also necessary because the transmitter unit has to be housed in a metallic cabinet to protect the frequency drift caused due to stray EM fields. Four key switches (DPST push-to-on spring loaded) are required to transmit the desired DTMF tones. The switches when pressed generate the specific tone pairs as well as provide power to the transmitter circuit simultaneously. This way when the transmitter unit is not in use it consumes no power at all and the battery lasts much longer. The receiver unit consists of an FM receiver (these days simple and inexpensive FM kits are readily available in the market which work exceptionally well), a DTMF-to-BCD converter and a flip-flop toggling latch section.

The frequency modulated DTMF signals are received by the FM receiver and the output (DTMF tones) are fed to the dedicated IC KT3170 which is a DTMF-to-BCD converter. This IC when fed with the DTMF tones gives corresponding BCD output; for example, when digit 1 is pressed, the output is 0001 and when digit 4 is pressed the output is 0100. This IC also requires a 3.58MHz crystal for its operation. The tone input is connected to its pin 2 and the BCD outputs are taken from pins 11 to 14 respectively. These outputs are fed to 4 individual �D� flip-flop latches which have been converted into toggle flip-flops built around two CD4013B ICs. Whenever a digit is pressed, the receiver decodes it and gives a clock pulse which is used to toggle the corresponding flip-flop to the alternate state. The flip-flop output is used to drive a relay which in turn can latch or unlatch any electrical appliance. We can upgrade the circuit to control as many as 12 channels since IC UM91214B can generates 12 DTMF tones. For this purpose some modification has to be done in receiver unit and also in between IC2 and toggle flip-flop section in the receiver. A 4-to-16 lines demultiplexer (IC 74154) has to be used and the number of toggle flip-flops have also to be increased to 12 from the existing 4

Motorcycle Alarm Number 2

2009-02-24T23:20:00.000-08:00

This circuit features an intermittent siren output and automatic reset. It can be operated manually using a key-switch or a hidden switch; but it can also be wired to set itself automatically when you turn-off the ignition. By adding external relays you can immobilize the bike, flash the lights etc. Ron has used my Asymmetric Timer as the basis for his design.
Notes:
Any number of normally-open switches may be used. Fit "tilt" switches that close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc.

Once activated, the rate at which the siren switches on and off is controlled by R7, R8 & C4. For example, increasing R7 will make the sound period longer; while increasing R8 gives longer silent periods.

While at least one switch remains closed the siren will sound. About one minutes after all of the switches have been opened, the alarm will reset. How long it takes to switch off depends on the characteristics of the actual components used. You can adjust the time to suit your requirements by changing the value of R4 and/or C1.

The circuit is designed to use an electronic Siren drawing 300 to 400mA. It's not usually a good idea to use the bike's own Horn because it can be easily located and disconnected. However, if you choose to use the Horn, remember that the alarm relay is too small to carry the necessary current. Connect the coil of a suitably rated relay to the "Siren" output. This can then be used to sound the Horn, flash the lights etc.

The Support Material for this alarm includes a detailed guide to the construction of the circuit-board, a parts list, a complete circuit description and more. The circuit board and switches must be protected from the elements. Dampness or condensation will cause malfunction. The components are all drawn lying flat on the board - but those connected between close or adjacent tracks are mounted standing upright. The links are bare copper wire on the component side. Two of the links must be fitted before the IC. A more detailed guide to the board's construction and a circuit description are available on request.

Connect a 1-amp in-line fuse AS CLOSE AS POSSIBLE to your power source. This is VERY IMPORTANT. The fuse is there to protect the wiring - not the alarm. Exactly how the system is fitted will depend on the make of your particular machine - so I'm unable to provide any further help or advice in this regard.

You can use a key-switch or a hidden switch to set the alarm - or you could use the normally-closed contacts of a small relay. Wire the relay coil so that it's energized while the ignition is on. Then every time you turn the ignition off - the alarm will set itself. The quiescent (standby) current is virtually zero - so there is no drain on the battery.

Add an Automatic Immobilizer.

Before fitting this or any other immobilizer to your bike, carefully consider both the safety implications of its possible failure - and the legal consequences of installing a device that could cause an accident.

If you decide to proceed, you will need to use the highest standard of materials and workmanship. Remember that the relay MUST be large enough to handle the current required by your ignition system. Choose one specifically designed for automobiles - it will be protected against the elements and will give the best long-term reliability. You don't want it to let you down on a cold wet night - or worse still - in fast moving traffic!!! Please note that I am UNABLE to help any further with either the choice of a suitable relay - or with advice on its installation.

When you turn-off the ignition, the relay will de-energize and the first set of contacts (RLA1) will break the ignition circuit - automatically immobilizing the bike. The second set of contacts (RLA2) will turn-on the alarm.

When the ignition is switched on again the relay will not energize. The bike's ignition circuit will remain broken; and the alarm will continue to protect the machine. You must press Sw2 to energize the relay. It then latches itself on using the first set of contacts (RLA1). The same set of contacts completes the connection to the ignition circuit; while the second set of contacts (RLA2) opens and switches off the alarm.

The design has a number of advantages. It operates automatically when you turn-off the ignition - so there's no need to remember to activate it. The relay uses no current while the ignition is off - so there's no drain on the battery. To de-activate it you'll need to have the ignition key and you'll need to know the whereabouts of the push-switch. For extra security Sw2 could be key-operated.

Water Level Alarm

2009-02-24T23:09:00.000-08:00

A circuit that offers visual indication of fluid level in a vessel, with a switchable audible alarm. Example uses would be to monitor the level of water in a bath or cold storage tank.
The conductance of fluids:
Conductance is the reciprocal of resistance. The conductance of fluids vary with temperature, volume and separation distance of the measurement probes. Tap water has a conductance of about 50 uS / cm measured at 25 � C. This is 20k/cm at 25 � C. See this site for more details about the conductance of fluids.

Notes:
This circuit will trigger with any fluid with a resistance under 900K between the maximum separation distance of the probes. Let me explain further. The circuit uses a 4050B CMOS hex buffer working on a 5 volt supply. All gates are biased off by the 10M resistors connected between ground and buffer input. The "common" probe the topmost probe above probe 1 in the diagram above is connected to the positive 5 volt supply. If probe 1 is spaced 1 cm away from the common probe and tap water at 25 � C is detected between the probes (a resistance of 20k) then the top gate is activated and the LED 1 will light. Similarly if probe 2 at 2 cm distance from the common probe detects water, LED 2 will light and so on. Switch 1 is used to select which output from the hex buffer will trigger the audible oscillator made from the gates of a CMOS 4011B IC.

Placement of Probes:
As 7 wires are needed for the probe I reccommend the use of 8 way computer ribbon cable. The first two wires may be doubled and act as the common probe wire. Each subsequent wire may be cut to required length, if required a couple of millimetres of insulation may be stripped back, though the open "cut off" wire end should be sufficient to act as the probe. The fluid and distance between probe 6 and the common probe wire must be less than 900k. This is because any voltage below 0.5 Volt is detected by the CMOS IC as logic 0. A quick potential check using a 900k resistance and the divider formed with the 10M resistor at the input proves this point:

5 x (0.9 / (0.9+10) = 0.41 Volt.

As this voltage is below 0.5 volt it is interpreted as a logic 0 and the LED will light. If measuring tap water at 25 � C then the distance between top probe and common may be up to 45 cm apart. For other temperatures and fluids, it is advisable to use an ohmmeter first. When placing the probes the common probe must be the lowest placed probe, as the water level rises, it will first pass probe 1, then 2 and finally probe 6.

Motorcycle Alarm

2009-02-24T22:57:00.000-08:00

Notes:

Any number of normally open switches may be used. Fit the mercury switches so that they close when the steering is moved or when the bike is lifted off its side-stand or pushed forward off its centre-stand. Use micro-switches to protect removable panels and the lids of panniers etc. While at least one switch remains closed, the siren will sound. About two minutes after the switches have been opened again, the alarm will reset. How long it takes to switch off depends on the characteristics of the actual components used. But, up to a point, you can adjust the time to suit your requirements by changing the value of C1.

The circuit board and switches must be protected from the elements. Dampness or condensation will cause malfunction. Without its terminal blocks, the board is small. Ideally, you should try to find a siren with enough spare space inside to accommodate it. Fit a 1-amp in-line fuse close to the power source. This protects the wiring. Instead of using a key-switch you can use a hidden switch; or you could use the normally closed contacts of a small relay. Wire the relay coil so that it is energized while the ignition is on. Then every time you turn the ignition off, the alarm will set itself.

When it's not sounding, the circuit uses virtually no current. This should make it useful in other circumstances. For example, powered by dry batteries and with the relay and siren voltages to suit, it could be fitted inside a computer or anything else that's in danger of being picked up and carried away. The low standby current and automatic reset means that for this sort of application an external on/off switch may not be necessary.

The Support Material for this alarm includes a detailed guide to the construction of the circuit-board, a parts list, a complete circuit description and more.

ဉာဏ္ရွိသလို အသံုးျပဳရန္ ရည္ရြယ္ပါသည္။

2009-02-24T01:28:00.000-08:00

အလင္း အာရံုခံ ဆင္ဆာေလးနဲ႕ အလုပ္လုပ္တဲ့ ဆားကစ္ေလးပါ.... မူရင္းေလးက ဒီလိုဗ်...

A light dependent resistor, LDR, could be used as part of a light sensor circuit. A tilt switch could be attached to the lid of the tin. Alternatively, you might attach a magnet to the lid of the tin and arrange for this to operate a magnetic switch (or reed switch). These devices would be part of a movement sensor subsystem.

Most alarms 'remember' that the sensor subsystem has been triggered. Closing the tin won't stop the alarm. A subsystem with this 'remembering' function is called a bistable, or latch.

Once you know the names and properties of the most important subsystems, you can use these building blocks to work out how to solve the design problem in outline.

How is this system going to work?

The sensor detects the opening of the tin. The output of the sensor triggers the latch so that its output goes HIGH. The reset subsystem provides some way of silencing the alarm.

An astable is a subsystem which produces pulses.

You may know about AND gates already. These follow a truth table where the output of the gate only becomes HIGH when both inputs are HIGH. ('HIGH' and 'LOW' in logic circuits always refer to HIGH and LOW voltages.)

AND gate truth table:

input B	input A	output
0	0	0
0	1	0
1	0	0
1	1	1

The AND gate is used in this system to decide whether pulses from the astable will be transferred to the audible warning device. If the output of the latch is LOW, no signals reach the audible warning device and the alarm is silent. On the other hand, if the circuit is triggered by opening the tin, the output of the latch becomes HIGH and the alarm sounds.

Work through the truth table of the AND gate to make sure you understand how this works.

Design Electronics includes details of all these subsystems. It's important to start building circuits straight away, so don't worry if you don't know about or understand everything all at once. For the moment, you need to concentrate on the skills involved in component identification, building prototype circuits, making measurements and soldering.

Sensor :
Sensor circuits almost always involve voltage divider circuits:

Which of these circuits gives an increase in V_out from LOW (logic 0) to HIGH (logic 1) when the tin is opened?

Which circuits give a decrease in V_out from HIGH (logic 1) to LOW (logic 0) when the tin is opened?

When the LDR is in the dark, substitute a big resistance, say 1 MW, in the formula. When the LDR is in the light, substitute a small resistance, say 1 kW. What size of resistance should be substituted when the tilt switch is closed?

Build a light sensitive voltage divider circuit on prototype board, as follows:

Confirm that this circuit gives a LOW voltage output when the LDR is exposed to light. There is a reason why you want a LOW output in the light which will become clear shortly.

Latch

One way of making a latch, also called a set-reset bistable, or set-reset flip flop involves two NAND gates. The symbol and truth table for an individual NAND gate are:

NAND gate symbol

NAND gate truth table:

input B	input A	output
0	0	1
0	1	1
1	0	1
1	1	0

How does this differ from the truth table for AND?

Here is the circuit for a NAND gate latch:

Pressing the SET button forces the Q-output to beome HIGH. The Q-output will stay HIGH until the RESET button is pressed.

To see what is happening, the NOT Q output can be used to drive an LED. Remember that LEDs need a series resistor to limit the current flowing:

driving an LED

Change your prototype board circuit to include this circuit:

The latch circuit uses a 4093 Schmitt trigger NAND gate integrated circuit, with pin connections like this:

Look again at the circuit diagram of the latch and at the prototype board. Confirm that the links produce a pattern of connections on the prototype board which is identical to the the connections indicated by the circuit diagram.

Operate the SET and RESET switches. Write a sentence to describe the behaviour of the latch circuit:

Now modify your prototype board, using the LDR/voltage divider to replace the SET switch:

Cover the LDR with you hand. Press the RESET switch. What happens to the LED?

Now, uncover the LDR. What happens to the LED?

Cover the LDR once again. What happens to the LED?

Pressing RESET should make the LED go OFF. Uncovering the LDR should make the LED go ON. It should remain ON when the LDR is covered again. The latch 'remembers' that the circuit has been triggered.
How can you make the LED go OFF again?

You can arrange for the latch to be RESET automatically when the circuit is first switched ON. This is done using another voltage divider:

When the circuit is first switched ON, V_out is LOW because the capacitor is empty. The capacitor charges up slowly through the 1 MW resistor. If this resistor/capacitor combination is used to replace the RESET switch on the prototype board, you will find that the LED remains OFF for several seconds when the power supply is first connected:

If the LDR is covered during this time, the latch will not be triggered. The LED remains OFF until the LDR is suddenly uncovered.

This is exactly the behaviour you want for the biscuit tin alarm. When the battery is first connected, the power on RESET prevents the latch from being triggered. This is when you put the circuit into the tin and close the lid. Inside the tin, the capacitor charges up and the circuit becomes ready to operate, waiting for the hungry biscuit thief. As soon as the lid is opened . . .

Astable

Astables produce pulses. One of the simplest astable circuits needs just one resistor and one capacitor together with a Schmitt trigger NAND gate:

Add this circuit to your prototype board using a 10 kW resistor and a 100 nF capacitor:

You can monitor the output pulses using an oscilloscope, as indicated. The frequency of the pulses should be around 1 kHz, that is, one thousand pulses per second.

AND gate

In the original block diagram, the latch and astable outputs are both connected to the inputs of an AND gate. Pulses from the astable are transferred to the output of the AND gate when the output of the latch becomes HIGH. You can think of the latch as providing a control input which determines whether the astable pulses get through.

NAND gates can be used to control the transfer of astable pulses in a very similar way. Look at the circuit diagram:

You have assembled most of the subsystems required by the block diagram. Modify your prototype board so that it looks like this:

Output
To complete the biscuit tin alarm, you need to add an audible warning device. This will be louder when driven via a transistor. The circuit is:

The transistor pin connections are:

Complete the circuit on prototype board as follows:

You have done extremely well if you have followed through the design process and built your biscuit tin alarm in prototype form. It is important to note that the development of the circuit is progressive. You start with just one subsystem on the prototype board and add further subsystems one at a time, testing the circuit and making modifications as you go along.

Final circuit
Prototype board testing leads eventually to a complete circuit for the device being developed. You can continue to make small alterations until the circuit behaves in the way you want.

The final circuit for the biscuit tin alarm is:

There are one or two alterations from the prototype board circuit you tested. A 10 kW preset resistor has been included. The resistance of the preset is adjusted using a screwdriver when the circuit is first assembled on printed circuit board and allows you to change the frequency of the astable pulses. This is useful because the piezo transducer oscillates more strongly at some frequencies than others. If you 'tune' the astable pulses to coincide with one of these resonant frequencies the noise produced is much louder.

A decoupling capacitor, 100 µF, has been added across the power supply. This helps to prevent the transfer of noise signals or 'spikes' along the power supply lines. It is good practice to include decoupling capacitors in your circuits. Do this even if you don't understand exactly what the capacitors are for!

Printed circuit board
Printed circuit board design involves locating the components which make up the circuit so that they can be easily soldered into the printed circuit board, or pcb, without wasting too much space. The pattern of copper tracks links the components together in the correct way.

Sometimes, the physical arrangement of components looks similar to the circuit diagram, so that you can work out which bit of the circuit is which. On the other hand, when the components are arranged around an integrated circuit ('beastie'), it can be difficult to identify different sections of the circuit. What matters is that the connections between components really are the same.

Designing printed circuit boards is a skill which you can learn. A good way to start is by looking carefully at the pcb's you use for your first soldered projects.

This is the printed circuit board design for the biscuit tin alarm:

Note that the track pattern for a pcb is usually visualised looking through the board as if it was transparent. This means that you can compare the component positions directly with the track layout.

^{PCB available}

Printed circuit boards for the biscuit tin alarm are available from DOCTRONICS. Please email for details.

White LED Night Light

2009-02-24T00:55:00.000-08:00

As many of you know, I have a pet peeve with poorly made LED night lights. Often, the light from the LED quickly fades, so within months, the light is useless. I have posted several versions of modified night lights using higher quality components. This circuit is yet another version, which produces much more light than those other designs. The circuit brings together two high power white LEDs made by Cree with a compact AC to DC power supply from Bias Power.

This simple circuit uses a one watt power supply module from Bias Power, model BPS1-08-00. The tiny module can crank out about 8 volts DC, fully isolated form the AC power line, whose voltage can range from 85vac to 250vac. The DC output of the module is fed to two one watt white LEDs, from Cree, wired in series. A 13 ohm � watt resistor in series limits the LED current to about 125ma. Although the LEDs are rated at one full watt, the circuit routes only one half watt into each part. The result is more than enough light for a night light and it should allow the light to last for many years.

I suggest mounting the two LEDs onto an aluminum bar or plate, to act as a heat sink. Excessive heat will shorten the life of the LED. You can remove the guts of a suitable night light and replace the internal parts with this circuit.

You can buy the Bias Power module at the address shown below. The Cree LEDs can be purchased from eBay. Other one watt LEDs may also work but may not last as long.

Click on Drawing Below to view PDF version of Schematic

Light Flasher

2009-02-24T00:41:00.001-08:00

This is a very basic circuit for flashing one or more LEDS and also to alternately flash one or more LEDs. It uses a 555 timer setup as an astable multivibrator with a variable frequency. With the preset at its max. the flashing rate of the LED is about 1/2 a second. It can be increased by increasing the value of the capacitor from 10uF to a higher value. For example if it is increased to 22uF the flashing rate becomes 1 second.
There is also provision to convert it into an alternating flasher. You just have to connect a LED and a 330ohm as shown in Fig.2 to the points X and Y of Fig.1. Then both the LEDs flash alternately.
Since the 555 can supply or sink in upto 200mA of current, you can connect upto about 18 LEDS in parallel both for the flasher and alternating flasher (that makes a total of 36 LEDs for alternating flasher).

1.5V LED FLASHER VERSION B

2009-02-24T00:06:00.000-08:00

To squeeze even more energy from a alkaline battery cell, this circuit adds two transistors to a circuit similar to the above design to boost the efficiency. A small 1.5 volt alkaline N cell should flash the LED for a full year. It too uses a "charge pump" technique to provide a LED the needed voltage.

Click on Drawing Below to view PDF version of Schematic

1.5V LED FLASHER (A)

2009-02-23T23:56:00.000-08:00

Many published circuits that flash LEDs need 3 volts or more. This circuit uses only a single inexpensive C-MOS IC and flashes the LED for a full year on a single 1.5 volt AA alkaline battery cell. The circuit uses a charge pump technique to provide the LED the needed voltage.

555 Timer-Based Flyback Transformer Driver

2009-02-22T23:05:00.000-08:00

My 24kV high voltage "Jacob's Ladder" from DIY flyback transformer driver using 555 timer.

Creating an electric arc

I've always wanted to create an electric arc but don't know how. Then I come across the theory that air breaks down at about 1MV/m (Mega Volts per meter) (24kV/in). That mean you need 1kV in order to get 1mm arc. So you need a higher voltage. One of the method is to use a flyback transformer that can be found from an old TV or an old CRT PC monitor. It could generate about 10 to 30 kV. Other method is to create a "tesla coil" which is quite complicated. Maybe it will become my next project.

Flyback transformer and preparation

Flybacks can be found in all types of monitors and screens that use a cathode ray tube (CRT), e.g. TV sets, computer monitors etc. It has a big red cable with a suction cup. It looks something like below.

Next, you need to identify the primary and secondary pin out. Thanks to "Lab HV-PS page" for providing an instruction on how to find the pinout. The main HV out on the secondary coil is a big red cable with a suction cup. Now we need to find the 0V pinout for the secondary coil. The trick is to use a DC power supply. This is because the flyback secondary coil resistance is much too high. There is no way you could find it with ordinary digital multimeter.

So use your own understanding on the circuit below to find the 0V pinout. Give it about 12V and your meter should show some volts when you find the 0V pinout. For me, just to be safe, try to find a datasheet of the flyback transformer or try to find the TV or old CRT PC monitor service manual/schematics diagram to find the pinout like below. Most modern flybacks include built-in HV rectifier diode(s) and/or voltage multiplier (tripler) so output without additional components will be high voltage positive or somewhat smoothed HV DC. So, make sure your polarity is correct.

Unless you have one of these multimeter, you should get the resistance reading out of it. From my FLUKE 189 multimeter you can see that it shows more than a hundred Mega Ohm. That is why ordinary meter could not measure it because of it's limit. Below I test two types of flybacks with 112 Mega Ohm and the other about 522 Mega Ohm. Again, polarity is critical to get the reading.

To find the primary coil is a much simple than the secondary coil. The primary coil resistance is about 1 ohm and again I confirm this with a TV or old CRT PC monitor service manual/schematics diagram. In my case I could only get 0.45 ohm.

Creating the flyback driver (20kHz with 90% duty cycle)

Thanks to "Jonathan Filippi" for the idea. My circuit is quite different. I try to fix up the frequency and duty cycle with help from simulation software. I use "Electronic Workbench" to simulate the circuit which can generate about 20kHz with 90% duty cycle and I come out with this. Using 555 timer to generate 20kHz with 90% duty cycle. Next I try to put it on the breadboard and test the output from it. I get about 18kHz with 85% duty cycle. Jonathan Filippi is using 2N3904 and 2N3906 but I'm using c1815 (npn) and a1015 (pnp). I found out that you can use any multipurpose transistor and I could find it on my old TV board. For the MOSFET, Jonathan Filippi is using IRF840 but I'm using IRF630. You may try to find it's equivalent and experiment with it. Just make sure it is compatible if you want to use other types of MOSFETs. Find it's data sheet and compare the characteristic for both types of components.

Before assemble it, I test this circuit with a small transformer which I can find it on the same old TV board. Since I'm getting too excited, the quick test is to connect the output to the lowest resistance coil. I test it with a limit resistor and surprise, I can get a hundred volt out of that.

Next is to plan to transfer it to the stripboard/veroboard. Here is the stripboard layout and the assembled circuit board. Make sure you mount the MOSFET to a heat sink since it going to heat up while running/powering it up. Note that I put the 150 ohm "snubber" resistor and diode near the flyback. This is to suppress ("snub") electrical transients that might damage of the circuit.

Again, I test the assembled circuit board with the same small transformer and I could get a neon to light up. This mean I'm getting about hundred volts. Neon needs about 80V or higher in order to light up.

Test it out

Now it time to test it out. Get a high power supply for this test. Don't use an expensive lab power supply for this test. It might burn or damage. For me, I'm using a 12V DC battery charger that can give about 5 Amps. You may also try a car battery if you have one.

There is an arc!. At last, I could get an arc out of it. I try to measure the initial max. length and I could get about 24mm. Thus, it is about 24kV. Remember the theory 1MV/m?.

I measure the DC operating current. It is about 5 Amps. I've blown my DC power supply fuse in the process. Maybe I need a bigger power supply :-) . At least I've got some arcs.

Good luck!

Efficient flyback driver by IC 555 + IRF510

2009-02-22T22:56:00.000-08:00

This is a good and fairly efficient flyback driver circuit. All parts can be obtained easily from Radio Shack, including the MOSFET. This circuit uses a 555 timer IC to pulse a 2N2222 with square wave at a frequency that is set by the capacitor and the potentiometers. The 2N2222 then drives the gate of the MOSFET and the MOSFET delivers the pulse to the ten turn winding on the flyback. If you build this circuit you will have to adjust the potentiometers until you get the longest arc possible. The circuit will run from +12VDC to +15VDC at about 3A. The MOSFET must be heatsinked! This is important if you are going to run this for any decent amount of time. If the MOSFET still gets too hot or burns up you can place a 4 ohm (for a +12V supply) or a 5 ohm (for a +15V supply) between the source lead of the MOSFET and the primary on the flyback. Make sure that these resistors havethe proper power rating for the voltage and current that they will be carrying. The flyback should be wound with ten turns of 14-16 guage solid wire. Anchor it in with some electrical tape. Any previous primary windind should have already been removed before winding the new one.

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Read More source:
http://www.geocities.com/CapeCanaveral/Lab/5322/fbt2.htm

LED Thermometer

2009-02-22T01:38:00.000-08:00

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This LED thermometer is designed for in home use, to read temperatures between about 60 and 78 degrees Fahrenheit. It is based around a precision temperature sensor IC, the LM34DZ. This sensor require no calibration and can measure temperatures of between -50F and +300F. While the circuit shown here does not use the full range of that sensor, it can be modified to do so by simply changing the voltage reference to U2 at the sacrifice of precision.

Parts

Part	Total Qty.	Description	Substitutions
C1	1	1uF 25V Electrolytic Capacitor
C2	1	10uF 25V Electrolytic Capacitor
R1	1	2.2K 1/4W Resistor
R2, R5, R7	1	1K Trim Pot
R3	1	1K 1/4W Resistor
R4	1	1.5K 1/4W Resistor
R6	1	470 Ohm 1/4W Resistor
R8	1	100 Ohm Or 15 Ohm 1/4W Resistor (See Notes)
D1 - D10	10	LED
U1	1	LM34DZ Precision Fahrenheit Temperature Sensor
U2	1	LM3914 Bar/Dot Graph Driver IC
MISC	1	Board, Wire, Socket For U1 and U2, Case

Notes

The pinout of U1 depends on the version of the IC you purchase. These options are shown below:

You will want to build the circuit with U1 and U2 in sockets in order to be able to complete calibration (which requires removal of these ICs).
You can use any LED you want for D1 - D10, however blue LEDs have a higher voltage requirement so if you want to go blue for a modern look, they may appear more dim then red, yellow or green.
By leaving pin 9 of U2 disconnected, the graph will operate in dot mode and R8 should be 100 Ohm. If you build the circuit with pin 9 tied to 9V, the circuit will be in graph mode and R8 should be 15 Ohms.
To calibrate the circuit, you will need a voltmeter. Power the circuit up and let it sit for a few minutes for temperature to stabilize. Ground the negative lead of the meter and connect the positive lead to pins 6 and 7 of U2. Set R7 so the meter reads as close to 3.345V as possible. Now connect the positive lead of the meter to pin 4 of U2 and adjust R5 until the meter reads 2.545V. Finally, disconnect power to the circuit and remove U1 and U2 from their sockets. Measure the value of R3 with an ohmmeter and remember that value. Connect the ohmmeter across R1 and adjust R1 to a value of exactly 3 times the value of R3. Reinstall U1 and U2 and the circuit is ready for use.

Basic Electrical Circuits

2009-02-22T01:20:00.000-08:00

Electrical and Electronics :

Electrical Engineering encompasses Everything in Electronics. Communications, Computers etc. are further specializations of Electronics. So it is best to Identify Electrical Circuits with Electrical Designs which excludes Active Devices. It can include Electronic Products in the form of wireable modules.

So House and Factory wiring, Appliances like Ovens, Toasters, Power Generation and management; all these are electrical. Motors, Generators, Connectors, Relays, Contacters and Circuit Breakers are Electrical Components.

A Radio or Power Inverter is Electronic. When an Inverter or Electronic AC-DC Motor Drive is used in a Control panel or Power Supply system, that integration is shown as an Electrical Circuit. I feel Simple Consumer Electronic Circuits using Diodes, Transistors, SCR, Capacitors and Resistors can also be taken under electrical circuits; when they are used in Mains-Power or Household Appliances. Solar Energy related circuits also can be studied under Electrical Power Circuits.

In Electronics RF-Microwave and Communications is a specialization area, Computer Hardware, Software, Internet form another major domain. Networking and Wireless data communication overlaps both the above.

Power Electronics and Instrumentation are fundamental domains needed for many. Industrial Automation with Process Control Instrumentation is unique, but is supported by the fundamental domains. Many more finer areas like Robotics and Medical Electronics have a much sharper focus.

Below is a Electrical Control Panel, It has a Strip Chart Recorder which is electro-mechanical, It has a PLC Inside. A handheld PLC Programming unit. The computer is showing the Ladder Logic Program. PLC is based on a embedded uC. The DIN Controllers are Analog + Digital circuits. So you see it is a Electrical Control Panel with Electronics and the PLC Ladder Logic means, Software too.

This is a PID Controller based Control Panel using a PLC from GE Fanuc Automation. The Computer is a 386 40MHz with 40MB HDD.