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Place to find out electronic diagrams from biggers to engineers

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Speed-Limit Alert

5:50 AM

Speed-limit Alert

 Wireless portable unit
Adaptable with most internal combustion engine vehicles
 Parts:
R1,R2,R19 1K 1/4W Resistors
R3-R6,R13,R17 100K 1/4W Resistors
R7,R15 1M 1/4W Resistors
R8 50K 1/2W Trimmer Cermet
R9 470R 1/4W Resistor
R10 470K 1/4W Resistor
R11 100K 1/2W Trimmer Cermet (see notes)
R12 220K 1/4W Resistor (see notes)
R14,R16 68K 1/4W Resistors
R18 22K 1/4W Resistor
R20 150R 1/4W Resistor (see notes)
C1,C7 100µF 25V Electrolytic Capacitors
C2,C3 330nF 63V Polyester Capacitors
C4-C6 4µ7 25V Electrolytic Capacitors
D1,D5 Red LEDs 3 or 5mm.
D2,D3 1N4148 75V 150mA Diodes
D4 BZX79C7V5 7.5V 500mW Zener Diode
IC1 CA3140 or TL061 Op-amp IC
IC2 4069 Hex Inverter IC
IC3 4098 or 4528 Dual Monostable Multivibrator IC
Q1,Q2 BC238 25V 100mA NPN Transistors
L1 10mH miniature Inductor (see notes)
BZ1 Piezo sounder (incorporating 3KHz oscillator)
SW1 SPST Slider Switch
B1 9V PP3 Battery (see notes)
Clip for PP3 Battery

Device purpose:
This circuit has been designed to alert the vehicle driver that he has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving.
There is a strict relation between engine's RPM and vehicle speed, so this device controls RPM, starting to beep and flashing a LED once per second, when maximum fixed speed is reached.
Its outstanding feature lies in the fact that no connection is required from circuit to engine.

Circuit operation:
IC1 forms a differential amplifier for the electromagnetic pulses generated by the engine sparking-plugs, picked-up by sensor coil L1. IC2A further amplifies the pulses and IC2B to IC2F inverters provide clean pulse squaring. The monostable multivibrator IC3A is used as a frequency discriminator, its pin 6 going firmly high when speed limit (settled by R11) is reached. IC3B, the transistors and associate components provide timings for the signaling part, formed by LED D5 and piezo sounder BZ1. D3 introduces a small amount of hysteresis.

Notes:
D1 is necessary at set-up to monitor the sparking-plugs emission, thus permitting to find easily the best placement for the device on the dashboard or close to it. After the setting is done, D1 & R9 can be omitted or switched-off, with battery saving.
During the preceding operation R8 must be adjusted for better results. The best setting of this trimmer is usually obtained when its value lies between 10 and 20K.
You must do this first setting when the engine is on but the vehicle is stationary.
The final simplest setting can be made with the help of a second person. Drive the vehicle and reach the speed needed. The helper must adjust the trimmer R11 until the device operates the beeper and D5. Reducing car's speed the beep must stop.
L1 can be a 10mH small inductor usually sold in the form of a tiny rectangular plastic box. If you need an higher sensitivity you can build a special coil, winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former (e.g. a can). Extract the coil from the former and tape it with insulating tape making thus a stand-alone coil.
Circuit's current drawing is approx. 10mA. If you intend to use the car's 12V battery, you can connect the device to the lighter socket. In this case R20 must be 330R.
Depending on the engine's cylinders number, R11 can be unable to set the device properly. In some cases you must use R11=200K and R12=100K or less.
If you need to set-up the device on the bench, a sine or square wave variable generator is required.
To calculate the frequency relation to RPM in a four strokes engine you can use the following formula:
Hz= (Number of cylinders * RPM) / 120.
For a two strokes engine the formula is: Hz= (Number of cylinders * RPM) / 60.
Thus, for a car with a four strokes engine and four cylinders the resulting frequency @ 3000 RPM is 100Hz.
Temporarily disconnect C2 from IC1's pin 6. Connect the generator's output to C2 and Ground. Set the generator's frequency to i.e. 100Hz and regulate R11 until you hear the beeps and LED D5 flashes. Reducing the frequency to 99 or 98 Hz, beeping and flashing must stop.
This circuit is not suited to Diesel engines.
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Soft Musical Telephone Ringer

8:09 AM

Soft Musical Telephone Ringer

The normal telephone bell, at times (specially during night when one does not want to be disturbed), appears to be quite irritating. The circuit shown here converts the loud sounding bell into a soft and pleasing musical tone.
The incoming ring is detected by transistor T1 and components wired around it. In absence of ringing voltage, transistor T1 is cut off while transistor T2 is forward biased as resistor R2 is returned to the positive supply rails. As a result collector of transistor T2 is at near-ground potential and hence IC1 (UM66) is off. Also capacitor C2 is charged to a slightly positive potential.
During positive half of the ringing voltage, diode D1 forward biases transistor T1 and rapidly discharges capacitor C2 to near ground potential and cuts off transistor T2 which, in turn, causes IC1 to be forward biased and music signal is applied to base of transistor T3 which drives the speaker. During negative half of the ringing voltage, capacitor C2 cannot charge rapidly via resistor R2 and hence transistor T2 remains cut off during the ringing interval. Thus the soft musical note into the loudspeaker sounds in synchronism with the ringing signal. When handset is lifted off the cradle, the ringing voltage is no more available and hence the soft musical note switches off
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Telephone amplifier

8:03 AM
Telephone amplifier













While talking to a distant subscriber on telephone, quite often we feel frustrated when the voice of the distant subscriber is so faint that it is barely intelligible. To overcome the problem, circuit of an inexpensive amplifier is presented here. It can be assembled and tested easily. There is no extra power source needed to power up the circuit, as it draws power from the telephone line itself. The amplifier will provide fairly good volume for the telephone conversation to be properly heard in a living room. A volume control is included to adjust the volume as desired.
The circuit is built around IC LM386. Diodes D6 and D7 are used to limit the input signal strength. Transformer X1 is a transistor radio's output transformer used in reverse. Asoriginal secondary (output) winding is connected in series with the telephone lines, the speech signals passing through the lines cause change in the magnetic flux in the core of transformer and thereby induce signal voltage across the primary winding. This audio signal is used as input for IC LM386. Diodes D2 through D5 connected in bridge configuration constitute a polarity guard so that the amplifier is powered with correct polarity, irrespective of the line polarity, Zener diode D1 may have any breakdown voltage between 6 and 12 volts range. e.
There is no need of a separate power switch as the circuit energises (via the normally open contacts of the cradle switch) when one lifts the handset.
The circuit may be wired on a general-purpose PCB or by etching a PCB for this circuit.
The circuit can be easily tested by connecting a 6 volts supply to line terminals 1 and 2. A hissing sound will be heard from the loudspeaker. Now connect 6V AC from a transformer to terminals 1 and 2 and observe hum in the loudspeaker. The volume of the hum can be changed through potentiometer VR1. Diodes D6 and D7 limit the input below ± 700 mV.
The circuit is to be connected to the telephone lines in series with the telephone instrument, as shown in the figure
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Dark-activated LED or Lamp Flasher

7:59 AM
Dark-activated LED or Lamp Flasher
Simple photo-sensitive circuit
3V battery supply

Parts:
R1 Photo resistor (any type)
R2 100K 1/2W Trimmer Cermet
R3,R4 10K 1/4W Resistors
R5 470R 1/4W Resistor
R6 47R 1/4W Resistor
C1 220µF 25V Electrolytic Capacitor
D1 1N4148 75V 150mA Diode
D2 LED Any type and color (See Notes)
Q1,Q2 BC337 45V 800mA NPN Transistors
SW1 SPST Switch
B1 3V (Two 1.5V AA or AAA cells in series, etc.)
Circuit operation:
This circuit adopts the rather unusual Bowes/White emitter coupled multivibrator circuit. The oscillation frequency is about 1Hz and is set by C1 value. The LED starts flashing when the photo resistor is scarcely illuminated. The onset of flashing can be set by trimming R2.
Notes:
Best results in flashing frequency can be obtained using for C1 a value in the 100 to 1000µF range.
To drive a filament lamp the following changes must be made:
Use a 2.2 to 3V, 250-300mA lamp in place of the LED
R2 = 10K 1/2W Trimmer Cermet
R3, R4 = 1K 1/4W Resistors
R6 = 1R 1/4W Resistor
C1 = 470 to 1000µF 25V Electrolytic Capacitor
In LED-mode operation the stand-by current consumption is less than 400µA.
In Lamp-mode operation the stand-by current consumption is about 3mA.
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Touch Sense Door Alarm

7:53 AM
Touch Sense Door Alarm
Hangs up on the door-handle

Beeps when someone touches the door-handle from outside

Parts:

R1 1M 1/4W Resistor

R2 3K3 1 or 2W Resistor (See Notes)
R3 10K 1/2W Trimmer Cermet (See Notes)
R4 33K 1/4W Resistor
R5 150K 1/4W Resistor
R6 2K2 1/4W Resistor
R7 22K 1/4W Resistor
R8 4K7 1/4W Resistor
C1,C2 10nF 63V Ceramic or Polyester Capacitors
C3 10pF 63V Ceramic Capacitor
C4,C6 100nF 63V Ceramic or Polyester Capacitors
C5 2µ2 25V Electrolytic Capacitor
C7 100µF 25V Electrolytic Capacitor
D1,D2,D4 1N4148 75V 150mA Diodes
D3 5 or 3mm. Red LED
Q1,Q2,Q3,Q5 BC547 45V 100mA NPN Transistors
Q4 BC557 45V 100mA PNP Transistor
L1 (See Notes)
L2 10mH miniature Inductor
Hook (See Notes)
BZ1 Piezo sounder (incorporating 3KHz oscillator)
SW1,SW2 SPST miniature Slider Switches
B1 9V PP3 Battery
Clip for PP3 Battery

Device purpose:

This circuit emits a beep and/or illuminates a LED when someone touches the door-handle from outside. The alarm will sound until the circuit will be switched-off.
The entire circuit is enclosed in a small plastic or wooden box and should be hanged-up to the door-handle by means of a thick wire hook protruding from the top of the case.
A wide-range sensitivity control allows the use of the Door Alarm over a wide variety of door types, handles and locks. The device had proven reliable even when part of the lock comes in contact with the wall (bricks, stones, reinforced concrete), but doesn't work with all-metal doors.
The LED is very helpful at setup.

Circuit operation:

Q1 forms a free-running oscillator: its output bursts drive Q2 into saturation, so Q3 and the LED are off. When part of a human body comes in contact with a metal handle electrically connected to the wire hook, the body capacitance damps Q1 oscillations, Q2 biasing falls off and the transistor becomes non conducting. Therefore, current can flow into Q3 base and D3 illuminates. If SW1 is closed, a self-latching circuit formed by Q4 & Q5 is triggered and the beeper BZ1 is activated.
When the human body part leaves the handle, the LED switches-off but the beeper continues to sound, due to the self-latching behavior of Q4 & Q5. To stop the beeper action, the entire circuit must be switched-off opening SW2.
R3 is the sensitivity control, allowing to cope with a wide variety of door types, handles and locks.

Notes:

L1 is formed winding 20 to 30 turns of 0.4mm. diameter enameled copper wire on R2 body and soldering the coil ends to the resistor leads. You should fill R2 body completely with coil winding: the final turn's number can vary slightly, depending on different 1 or 2W resistor types actual length (mean dimensions for these components are 13-18mm. length and 5-6mm. diameter).
The hook is made from non-insulated wire 1 - 2mm. diameter (brass is well suited). Its length can vary from about 5 to 10cm. (not critical).
If the device is moved frequently to different doors, Trimmer R3 can be substituted by a common linear potentiometer fitted with outer knob for easy setup.
To setup the device hang-up the hook to the door-handle (with the door closed), open SW1 and switch-on the circuit. Adjust R3 until the LED illuminates, then turn slowly backwards the screwdriver (or the knob) until the LED is completely off. At this point, touching the door-handle with your hand the LED should illuminate, going off when the hand is withdrawn. Finally, close SW1 and the beeper will sound when the door-handle will be touched again, but won't stop until SW2 is opened.
In regular use, it is advisable to hang-up and power-on the device with SW1 open: when all is well settled, SW1 can be closed. This precautionary measure is necessary to avoid unwanted triggering of the beeper.
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Car Battery Tester

7:05 AM
Car Battery Tester
This circuit uses the popular and easy to find LM3914 IC. This IC is very simple to drive, needs no voltage regulators (it has a built in voltage regulator) and can be powered from almost every source.


This circuit is very easy to explain:
When the test button is pressed, the Car battery voltage is feed into a high impedance voltage divider. His purpose is to divide 12V to 1,25V (or lower values to lower values). This solution is better than letting the internal voltage regulator set the 12V sample voltage to be feed into the internal voltage divider simply because it cannot regulate 12V when the voltage drops lower (linear regulators only step down). Simply wiring with no adjust, the regulator provides stable 1,25V which is fed into the precision internal resistor cascade to generate sample voltages for the internal comparators. Anyway the default setting let you to measure voltages between 8 and 12V but you can measure even from 0V to 12V setting the offset trimmer to 0 (but i think that under 9 volt your car would not start). There is a smoothing capacitor (4700uF 16V) it is used to adsorb EMF noise produced from the ignition coil if you are measuring the battery during the engine working. Diesel engines would not need it, but I'm not sure. If you like more a point graph rather than a bar graph simply disconnect pin 9 on the IC (MODE) from power. 
The calculations are simple (default)
For the first comparator the voltage is : 0,833 V corresponding to 8 V
* * * * * voltage is : 0,875 V corresponding to 8,4 V
for the last comparator the voltage is : 1,25 V corresponding to 12 V
Have fun, learn and don't let you car battery discharge... ;-)
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Digital Volt-Meter (LED)

7:01 AM
Digital Volt-Meter (LED)

                                                                        [ front side ]
Copyright of this circuit belongs to smart kit electronics. In this page we will use this circuit to discuss for improvements and we will introduce some changes based on original schematic.

General Description
This is an easy to build, but nevertheless very accurate and useful digital voltmeter. It has been designed as a panel meter and can be used in DC power supplies or anywhere else it is necessary to have an accurate indication of the voltage present. The circuit employs the ADC (Analogue to Digital Converter) I.C. CL7107 made by INTERSIL. This IC incorporates in a 40 pin case all the circuitry necessary to convert an analogue signal to digital and can drive a series of four seven segment LED displays directly. The circuits built into the IC are an analogue to digital converter, a comparator, a clock, a decoder and a seven segment LED display driver. The circuit as it is described here can display any DC voltage in the range of 0-1999 Volts.

Technical Specifications - Characteristics
Supply Voltage: ............. +/- 5 V (Symmetrical)
Power requirements: ..... 200 mA (maximum)
Measuring range: .......... +/- 0-1,999 VDC in four ranges
Accuracy: ....................... 0.1 %

FEATURES
- Small size
- Easy construction
- Low cost.
- Simple adjustment.
- Easy to read from a distance.
- Few external components.

How it Works
In order to understand the principle of operation of the circuit it is necessary to explain how the ADC IC works. This IC has the following very important features:
- Great accuracy.
- It is not affected by noise.
- No need for a sample and hold circuit.
- It has a built-in clock.
- It has no need for high accuracy external components.
Schematic (fixed 22-2-04)
7-segment display pinout MAN6960


An Analogue to Digital Converter, (ADC from now on) is better known as a dual slope converter or integrating converter. This type of converter is generally preferred over other types as it offers accuracy, simplicity in design and a relative indifference to noise which makes it very reliable. The operation of the circuit is better understood if it is described in two stages. During the first stage and for a given period the input voltage is integrated, and in the output of the integrator at the end of this period, there is a voltage which is directly proportional to the input voltage. At the end of the preset period the integrator is fed with an internal reference voltage and the output of the circuit is gradually reduced until it reaches the level of the zero reference voltage. This second phase is known as the negative slope period and its duration depends on the output of the integrator in the first period. As the duration of the first operation is fixed and the length of the second is variable it is possible to compare the two and this way the input voltage is in fact compared to the internal reference voltage and the result is coded and is send to the display.

[back side]


All this sounds quite easy but it is in fact a series of very complex operations which are all made by the ADC IC with the help of a few external components which are used to configure the circuit for the job. In detail the circuit works as follows. The voltage to be measured is applied across points 1 and 2 of the circuit and through the circuit R3, R4 and C4 is finally applied to pins 30 and 31 of the IC. These are the input of the IC as you can see from its diagram. (IN HIGH & IN LOW respectively). The resistor R1 together with C1 are used to set the frequency of the internal oscillator (clock) which is set at about 48 Hz. At this clock rate there are about three different readings per second. The capacitor C2 which is connected between pins 33 and 34 of the IC has been selected to compensate for the error caused by the internal reference voltage and also keeps the display steady. The capacitor C3 and the resistor R5 are together the circuit that does the integration of the input voltage and at the same time prevent any division of the input voltage making the circuit faster and more reliable as the possibility of error is greatly reduced. The capacitor C5 forces the instrument to display zero when there is no voltage at its input. The resistor R2 together with P1 are used to adjust the instrument during set-up so that it displays zero when the input is zero. The resistor R6 controls the current that is allowed to flow through the displays so that there is sufficient brightness with out damaging them. The IC as we have already mentioned above is capable to drive four common anode LED displays. The three rightmost displays are connected so that they can display all the numbers from 0 to 9 while the first from the left can only display the number 1 and when the voltage is negative the «-« sign. The whole circuit operates from a symmetrical ρ 5 VDC supply which is applied at pins 1 (+5 V), 21 (0 V) and 26 (-5 V) of the IC.


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 component’s body and insert the 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.
[Parts placement]

PCB dimensions: 77,6mm x 44,18mm or scale it at 35%


- 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.

As it is recommended start working by identifying the components and separating them in groups. There are two points in the construction of this project that you should observe:
First of all the display IC’s are placed from the copper side of the board and second the jumper connection which is marked by a dashed line on the component side at the same place where the displays are located is not a single jumper but it should be changed according to the use of the instrument. This jumper is used to control the decimal point of the display.
If you are going to use the instrument for only one range you can make the jumper connection between the rightmost hole on the board and the one corresponding to the desired position for the decimal point for your particular application. If you are planning to use the voltmeter in different ranges you should use a single pole three position switch to shift the decimal point to the correct place for the range of measurement selected. (This switch could preferably be combined with the switch that is used to actually change the sensitivity of the instrument).
Apart from this consideration, and the fact that the small size of the board and the great number of joints on it which calls for a very fine tipped soldering iron, the construction of the project is very straightforward.
Insert the IC socket and solder it in place, solder the pins, continue with the resistors the capacitors and the multi-turn trimmer P1. Turn the board over and very carefully solder the display IC’s from the copper side of the board. Remember to inspect the joints of the base of the IC as one row will be covered by the displays and will be impossible to see any mistake that you may have made after you have soldered the displays into place.
The value of R3 controls in fact the range of measurement of the voltmeter and if you provide for some means to switch different resistors in its place you can use the instrument over a range of voltages.


For the replacement resistors follow the table below:
0 - 2 V ............ R3 = 0 ohm 1%
0 - 20 V ........... R3 = 1.2 Kohm 1%
0 - 200 V .......... R3 = 12 Kohm 1%
0 - 2000 V ......... R3 = 120 Kohm 1%
When you have finished all the soldering on the board and you are sure that everything is OK you can insert the IC in its place. The IC is CMOS and is very sensitive to static electricity. It comes wrapped in aluminium foil to protect it from static discharges and it should be handled with great care to avoid damaging it. Try to avoid touching its pins with your hands and keep the circuit and your body at ground potential when you insert it in its place.
Connect the circuit to a suitable power supply ρ 5 VDC and turn the supply on. The displays should light immediately and should form a number. Short circuit the input (0 V) and adjust the trimmer P1 until the display indicates exactly «0».


Parts 
R1 180k 
R2 22k 
R3 12k 
R4 1M 
R5 470k 
R6 560 Ohm 
C1 100pF 
C2, C6, C7 100nF 
C3 47nF 
C4 10nF 
C5 220nF 
P1 20k trimmer multi turn
U1 ICL 7107 
LD1,2,3,4 MAN 6960 common anode led displays


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.


Sample Power supply 1 
Sample Power supply 2
author: Smart Kit




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Pulsing Third Brake Light

5:31 AM
Pulsing Third Brake Light
Parts
IC1,IC2 = 555 Timer, RS #276-1723
SCR1 = NTE/ECG5402, RS #276-1067, EC103A, MCR104, etc.
Q1 = NTE/ECG197, SK3083, TIP125, or equivalent
D1,D2,D3 = 1N4148, 1N914, NTE/ECG519, RS #276-1122
D4,D5 = 1N5400, NTE/ECG5850, RS #276-1141, or equivalent
R1 = 18K
R2 = 330 ohm (RS #271-1315)
R3 = 270K
R4 = 82K
R5,R6 = 1K2
R8 = 100 ohm (RS# 271-1311)
P1 = 50K, 10-turn
P2 = 10K, 10-turn
C1 = 100µF/16V (RS# 272-1016)
C2 = 22µF/16V (RS# 272-1014)
C3 = 220µF/16V (RS# 272-1017)
C4 = 10µF/16V (RS# 272-1013)
Q1 is a PNP Silicon Audio Power Out/Medium Power Switch Transistor, 7A, with a TO-220 case. As long as you have a transistor which is close it will work fine. The SCR is a 100vrm, 0.8A, sensitive gate with a TO-92 case. Diodes D1, D2 and D3 are standard small signal diodes. Power diodes D4 and D5 are the 6A, 50prv types, cathode case. The 60vrm type will work as well. I used for IC1 & IC2 the LM555 type. P1 controls the 'on' and pulse-duration, P2 controls the pulse-timing.

Applying the Brakes: 
When you first press the brakes, this circuit will turn on your 3rd brake light via the main brake lights. After about a second a series of short strobe pulses occur. The number of pulses range from approximately 1 to 10, depending on the setting of P1/P2 and when the brake pedal was applied last. After the pulses have been applied the third brake light assumes normal operation. The prototype was set for five flashes which seemed more than enough. Two days later I re-adjusted the trimmer potentiometers for 4 flashes--1/2 second pause--4 flashes. Looks pretty cool!

Circuit Description:
The schematic consists of two 555 timer/oscillators in a dual timer configuration both setup in astable mode. When power is applied via the brake pedal, the brake light driver Q1 is switched on via the low-output pin 3 of IC2, and timer IC1 begins its timing cycle. With the output on pin 3 going high, inhibiting IC2's pin 2 (trigger) via D2, charge current begins to move through R3, R4 and C2.
When IC1's output goes low, the inhibiting bias on pin 2 of IC2 is removed and IC2 begins to oscillate, pulsing the third brake light via the emitter of Q1, at the rate determined by P2, R6, and C4. That oscillation continues until the gate-threshold voltage of SCR1 is reached, causing it to fire and pull IC1's trigger (pin 2) low. With its trigger low, IC1's ouput is forced high, disabling IC2's trigger. With triggering disabled, IC2's output switches to a low state, which makes Q1 conduct turning on the 3rd Brake Light until the brakes are released. Obviously, removing the power from the circuit at any time will reset the Silicon Controlled Rectifier SCR1, but the RC network consisting of R4 and C2 will not discharge immediately and will trigger SCR1 earlier. So, frequent brake use means fewer flashes or no flashes at all. But I think that's okay. You already have the attention from the driver behind you when you used your brakes seconds before that.
The collector/emitter voltage drop accross Q1 together with the loss over the series fed diodes D4/D5, will reduce the maximum available light output, but if your car's electrical system is functioning normally in the 13 - 14volt range, these losses are not noticeable.

Building Tips: 
You can easily build this circuit on perfboard or on one of RS/Tandy's experimentors boards (#276-150), or use the associated printed circuit board listed here.
Keep in mind that Q1 will draw most likely 2 or 3 amps and mounting this device on a heat sink is highly recommended. Verify that the scr is the 'sensitive gate' type. In incandecent bulbs, there is a time lag between the introduction of current and peak brightness. The lag is quite noticeable in an automotive bulb, so the duration of a squarewave driving such a bulb should be set long enough to permit full illumination. For that reason, and because lamps and car electrical systems vary, adjustment via P1 and P2 is necessary to provide the most effective pulse timing for your particular vehicle.
The reason that the third light is connected to both brake lights is to eliminate the possibility of a very confusing display when you use your turn signal with the brakes applied.
The cathode of D4 and D5 are tied together and go to point 'B' of the third brake light in the component layout diagram. Point 'A' goes to the other leg of the third brake light. Most if not all third brake lights in Canada & USA have two wires, the metal ones also have a ground wire which obviously goes to ground. I don't know the wiring schema for Australian and European third brake lights.
Don't forget the three jumpers on the pcb; two jumpers underneath IC1/IC2 between pin 4/8 and the one near Q1/R6.
If you use a metal case, don't forget to insulate the D4/D5 diodes.
Some 90's cars, like my 1992 Mercury Sable, have two bulbs inside the third brake light, each bulb is hooked up seperately to the left and right brake light for reasons only Ford knows. Click here for a possible 2-bulb hookup. It shows how I modified mine to get it working; and that was easier than I expected. Current draw with the two bulbs was measured at 1.85Amps (1850mA). Even with double the current none of the circuit components were getting hot. I had to re-adjust the two pots to make it flash since the bench testing was done with one bulb.

Bench Testing:
I tested different semiconductors like the 1N5401/1N5404, NTE153, and 4A type powerdiodes for D4/D5. All worked very well. As expected, Q1 is getting very hot. Current draw was measured between 680 - 735mA with a regular automotive 'headlight' bulb, extra heavy duty to make sure the circuit was safe. I tested several other power transistors including some darlingtons like the TIP125 and the TIP147. I eventually settled for the TIP125 myself because I had it available but any thing with 5A or more will do fine.
The actual third brake bulb is a lot smaller. Adjusting the trimpots (P1/P2) may take a bit of patience but really fine-tunes the circuit well. The only drawback of this circuit is the discharge lag coming from the electrolytic capacitor C2 and the R4 resistor. Especially if the brakes are used often or at short intervals the third brake light will not flash or maybe flash once or twice. Again, this is because the R-C combo does not have enough time to discharge in between braking. It takes about 12 seconds to discharge C2.


The pcb measures 2 x 2.5 inch (5 x 6.4cm or 170 x 200 pixels)
at 2 colors and is shown smaller when you print these pages.
If you need a direct, full size copy of the pcb I suggest to load the gif file into a program like Paint Shop Pro or one of the many gif viewers available.





The layout is enlarged a bit for a better component view. Note that Q1 is drawn soldered on the pcb but if you have a metal case you can put it anywhere on the metal case (as a coolrib) and use havy duty wiring between Q1 and the PCB.

CORRECTION: SCR1's anode/kathode
were shown reversed (fixed: 2-26-2000).
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Automatic Headlight Brightness Controller

5:25 AM
Automatic Headlight Brightness Controller   
Parts:
R1 5K 1/4W Resistor
R2, R3, R4 5K Pot
Q1 NPN Phototransistor
Q2 2N3906 PNP Transistor
K1 Low Current 12V SPST Relay
K2 High Current 12V SPDT Relay
S1 SPST Switch
B1 Car Battery
MISC Case, wire, board, knobs for pots


Notes:
1. Q1 should me mounted in such a way so it points toward the front of the car with a clear line of site. Suitable places are on the dashboard, in the front grill, etc.
2. Adjust all the pots for proper response by testing on a deserted road.
3. S1 enables and disables the circuit.
4. B1 is, obviously, in the car already.
5. Before you try to connect this circuit, get a wiring diagram for your car. Some auto manufacturers do weird things with wiring.
6. Connection A goes to the high beam circuit, B goes to the headlight switch common and C connects to the low beam circuit.
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Night Rider Lights

5:21 AM
Night Rider Lights
As a keen cyclist I am always looking for ways to be seen at night. I wanted something that was a novelty and would catch the motorists eye. So looking around at my fellow cyclists rear lights, I came up with the idea of 'NITE-RIDER'. NINE extra bright LED's running from left to right and right to left continuously. It could be constructed with red LEDs for use on the rear of the bike or white LED's for an extra eye catcher on the front of the bike.
All IC's are CMOS devices so that a 9V PP3 battery can be used, and the current drawn is very low so that it will last as long as possible.

Parts
1 555 timer IC4.
1 4027 flip flop IC1.
2 4017 Decade Counter IC2 and IC3.
3 4071 OR gate IC5, IC6 and IC7.
1 470 Ohm resistor 1/4 watt R3.
2 10K resistors 1/4 watt R1 and R2.
1 6.8UF Capasitor 16V C1.
9 Super brght LED's 1 to 9.
1 9V PP3 Battery.
1 single pole switch SW1.
1 Box.

How The Circuit Works.
IC4, C1, R1 and R2 are used for the clock pulse which is fed to both the counters IC2 and IC3 Pin 14.
IC1 is a Flip Flop and is used as a switch to enable ether IC2 or IC3 at pin 13.
IC7a detects when ether IC2 or IC3 has reached Q9 of the counter pin 11.
IC5, IC6 and IC7a protects the outputs of the counters IC2 and IC3 using OR gates which is then fed to the Anodes of the
LED's 1 to 9.
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PIC diode tester

6:02 AM

PIC diode tester

This is a simple use of the PIC 16F84 about a diode tester.
Test procedure : We set «1» to PB0 and «0» to PB3. If diode is ok and opens, then at PA0 we have «1». If PA0 is «0», then the the diode has problem. With the program we manage what the PIC will do in each situation . If PA0 is «1», green led lights wich means that the diode is OK and if PA0 is «0» red led is lighting and the diode is problematic

Test continuous as follows: We give «0» at PB0 and «1» to PB3. If diode is OK and opens, then at PA0 is «1». If PA0 is «0», then diode has problem. If PA0 is «1», green led lights that means that diode is OK and if PA0 is «0» the red diode is lights that means the the diode is problematic.

Source Code
Credit of this diagram goes to Mr. Manolis Xenias
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iButton electronic lock

5:57 AM

iButton electronic lock

Since iButton DS1990A introduced in market from Dallas Semiconductor (MAXIM), it has been used in many applications concerning security, access control systems etc. In this project we will use iButton as a key to an electronic lock. This electronic lock can use many different kinds of iButtons and can store up to 9 different keys. One of the keys is the master key and is permanent stored in memory. With the use of master key we can add or remove slave keys.
This electronic lock can be used with any type of iButtons you may already have, since the only thing needed is the internal serial number, that's different for every iButton. The command used to read the serial number is the same for all iButtons. The iButton family code that goes with every iButton, can be anything and is calculated as part of the whole serial number. We must also notice that DS1990A series iButtons are the cheapest.

This electronic lock designed to work stand-alone and it's easy to construct. What the user sees (outside of the door for example) is a iButton socket and a led. From inside the door, we can open it using a simple push button. For the actual lock of the door a solenoid and a bold are used. Solenoid must be rated at 12Vdc. iButtons serial numbers stored in memory can be removed and updated when needed. One master key is used to manage the rest of them. Totally a number of 9 different keys can be stored in memory.
Schematic diagram is shown at figure 1. The circuit is build around an Atmel AT89C2051(U1) microcontroller. The port 1 (P1) of mcu is used to connect a 7-segment common anode led display. This led display will be used on the programming of additional keys. For the same reason a push-button labelled SB1 is connected on P.3.7. Storage of iButtons serial numbers is done on a 24C02 EEPROM (U3). It is connected on P3.4 (SDA) and P3.5 (SCL) of U1. The external iButton socked is connected on port P3.3 via XP2 pin array. The rest of components VD4, R3, VD5 and VD6 are used for protection of mcu ports. One pull-up resistor R4 is used as required from 1-wire protocol. An additional iButton socket is connected parallel with the predefined at pins XS1. This one is used for programming the keys. The door OPEN button is connected on P3.2 through XP1 connector, using the same protection components as above. The solenoid that does the lock is connected on XT1 connector. Solenoid is controlled from a power MOSFET IRF540 (VT3). Diode VD7 is added to protect MOSFET from voltage strikes due to solenoid inductance. Transistor VT3 is controlled from VT2, which reverses the logic state that's appears on P3.0, so on VT3 we have output 0V and 12V. This additional transistor is useful as it translates the mcu logic levels to 0V and 12V, capable to drive the solenoid.
Fig.1 Schematic diagram of iButton electronic lock
A led is used to indicate the state of the electronic lock, which is controlled from the same pin as the solenoid, using transistor TV1. This led is connected to the board using the same pin array XP2. But we need to ensure that the circuit will always work without supervision. For that reason we added ADM1232 (U2) that does the mcu reset pin control. This chip have a counter and voltage test circuits inside it. On pin P3.1 mcu produces pulses when it works right. If for a reason mcu freeze then U2 send it a reset pulse and work is resumed.
This electronic lock has it's own power supply on board, consisting of transformer T1, bridge rectifier VD9-VD12 and voltage regulator U4. As power backup an array of 10 AA batteries is used (BT1-BT10). Total capacity is 800mAH. When the circuit is connected on main voltage the battery pack is charged via R10 with a current of 20mA. This current is equal to 0.025C (where C is the batteries capacity) and that's a very small current depending on total capacity. That's put the battery on a steady charge to compensate losses among time and no charge completion detection is needed. That can be done as the excess energy is consumed in heat, that can not harm batteries as its low.
Overall board dimensions are 150х100х60mm. The most components are placed on the board, including the transformer. Batteries are placed on battery holders. In the place of AA batteries we could use a 12V sealed Lead - Acid battery. External components are connected on board with 2 or 3 pin connectors. Part numbers HG1, SB1 and XS1 are used only in programming mode so can be placed inside the plastic enclosure. Led VD3 can be placed on the face of enclosure, to indicate proper powering of board. A connection diagram is show on figure 2.
Fig.2 Connection diagram
When the door goes open, a 3 sec pulse is triggering the solenoid. When we press the door open button the door remains open as long as we push it.
The electronic lock can register 9 keys, plus one master key. Master's serial number is stored inside mcu. The rest of keys are stored on the external memory under slot 1 to 9. To add or remove a new key you should have the master key. Also master key can be used to open the door.

Fig. 3 Programming steps for adding a new key
To add a new key, the following steps should followed:
1. Press programming button.
2. Led displays letter «P» that indicated you entered programming mode.
3. Touch the master button in socket.
4. Led displays number «1». That's the current selected slot in memory.
5. Push the programming button to select a different programming slot for your new key.
6. Touch the new key to the socket.
7. The number on led display blinks, indicating ready to program.
8. Touch again the new key to confirm registration to memory.
9. If successfully registered the display stops blinking.
10. After 5 seconds, the program exits from programming mode.

The programming procedure to register a new key is displayed schematically on figure 3.
If you want to register more keys, then from step 9 you can go directly to step 5. These steps can be revised as many times as you like.
If after step 7, you find out that you selected wrong slot number and you don't want to loose that key, press programming button or just wait 5 seconds. When you press the button the slot number increases by one and memory hasn't changed yet. If you wait 5 seconds, programming mode will exit and nothing is going to register in memory. Generally in any programming step, you can wait 5 second to exit programming mode.
To remove an already registered key, you follow an almost same procedure, using only the master key. Basically, it's like registering the master key on the memory slot you would like to erase. This procedure is shown on figure 4.

Fig.4 Programming steps for removing a key.
During programming mode, the door will only open with the press of the OPEN button. Also, because the two iButton sockets are connected in parallel, you should avoid simultaneous touch of keys on both sockets.
Master's key serial number is stored on mcu's program memory, beginning from address 2FDH. The length of serial number is 8 bytes. The serial must be equal that is printed on top the iButton case, reading from left to right. On memory address 2FDH the control byte is registered, then on address 2FEH - 303H the next six bytes are registered, beginning with most significant byte. Finally the family code byte is stored on address 304H. For example a complete serial code should look like: 67 00 00 02 D6 85 26 01
The software block diagram shows on figure 5. The program starts, asking if a key has entered. If a key is entered, then it goes on reading the internal serial number. The next step is to check if this is the master key or another key already registered in memory. If the key is verified then the door is opened. Also the OPEN push button is checked, and if it's pressed the door opens.
Fig.5 Software block diagram
For the programming mode there exists two subprograms: PROGT and PROGS, whose block diagrams show in figure 6. The first is called when the serial number is read, in the programming phase and the second is called when the programming button is pressed. Programming of a new key is completed in three phases. When we press the programming button, we enter the programming mode. In this state the led displays «P» and the serial number of the key is checked to see if this is the master key, because this key is required to proceed on programming steps.
If this is the master key, we proceed on phase 2. Now, led is displaying the number of current selected memory slot, changing by pressing programming button. If we touch the key again, then it is registering on memory and we pass to phase 3. If we touch another key, this is also registered and we pass to phase 2. With the press of the button, we pass on phase 2 without registering any key.
If we don't touch anything in a period of 5 seconds, the program exits from programming mode. Block diagrams of figure 5 and 6 are simplified, but they give as an overall sense of program functionality.
It's upon your desire to extend the capabilities of this program, as it's open source, to fit your special needs.
Please Download Files below;
                                                       1.)   Source code 
                                                       2.)   Binary File
                                                        3.)   Project Document MS-word file



The credit of this diagram goes to Mr. Leonid Ridiko and Victor Lapitskiy
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