রবিবার, ২৫ মে, ২০২৫
মঙ্গলবার, ২০ মে, ২০২৫
শনিবার, ১০ মে, ২০২৫
TRAIN DETECTORS
TRAIN DETECTORS In response to a reader who wanted to parallel TRAIN DETECTORS, here is a diode OR-circuit. The resistor values on each detector will need to be adjusted (changed) according to the voltage of the supply and the types of detector being used. Any number of detectors can be added. See Talking Electronics website for train circuits and kits including Air Horn, Capacitor Discharge Unit for operating point motors without overheating the windings, Signals, Pedestrian Crossing Lights and many more
LED DETECTS LIGHT
INCREASING THE OUTPUT CURRENT
INCREASING THE OUTPUT CURRENT The output current of all 3-terminal regulators can be increased by including a pass transistor. This transistor simply allows the current to flow through the collector-emitter leads. The output voltage is maintained by the 3-terminal regulator but the current flows through the "pass transistor." This transistor is a power transistor and must be adequately heatsinked. Normally a 2N3055 or TIP3055 is used for this application as it will handle up to 10 amps and creates a 10 amp power supply. The regulator can be 78L05 as all the current is delivered by the pass transistor.
CAMERA ACTIVATOR
CAMERA ACTIVATOR This circuit was designed for a customer who wanted to trigger a camera after a short delay. The output goes HIGH about 2 seconds after the switch is pressed. The LED turns on for about 0.25 seconds. The circuit will accept either active HIGH or LOW input and the switch can remain pressed and it will not upset the operation of the circuit. The timing c
BOOK LIGHT
DARK DETECTOR with beep-beep-beep Alarm
This circuit detects darkness and produces a beep-beep-beep alarm. The first two transistors form a high-gain amplifier with feedback via the 4u7 to produce a low-frequency oscillator. This provides voltage for the second oscillator (across the 1k resistor) to drive a speaker.
150 WATT AMPLIFIER CIRCUIT
Description This is the cheapest 150 Watt amplifier circuit you can make,I think.Based on two Darlington power transistors TIP 142 and TIP 147 ,this circuit can deliver a blasting 150 W Rms to a 4 Ohm speaker.Enough for you to get rocked?;then try out this. TIP 147 and 142 are complementary Darlington pair transistors which can handle 5 A current and 100V ,famous for their ruggedness. Here two BC 558 transistors Q5 and Q4 are wired as pre amplifier and TIP 142 ,TIP 147 together with TIP41 (Q1,Q2,Q3) is used for driving the speaker.This circuit is designed so rugged that this can be assembled even on a perf board or even by pin to pin soldering.The circuit can be powered from a +/-45V, 5A dual power supply.You must try this circuit.Its working great! The preamplifier section of this circuit is based around Q4 and Q5 which forms a differential amplifier. The use of a differential amplifier in the input stage reduces noise and also provides a means for applying negative feedback. Thus overall performance of the amplifier is improved. Input signal is applied to the base of Q5 through the DC decoupling capacitor C2. Feedback voltage is applied to the base of Q4 from the junction of 0.33 ohm resistors through the 22K resistor. A complementary Class AB push-pull stage is built around the transistors Q1 and Q2 for driving the loud speaker. Diodes D1 and D2 biases the complementary pair and ensures Class AB operation. Transistor Q3 drives the push-pull pair and its base is directly coupled to the collector of Q5.
Notes. Remember TIP 142 and 147 are Darlington pairs .They are shown as conventional transistors in figure for ease.So don’t get confused.Even though each of them have 2 transistors ,2 resistors and 1 diode inside ,only three pins ,base emitter and collector are coming out.Rest are connected internally.So its quite OK to assume each of them as transistor for ease. Use a well regulated and filtered power supply. Connect a 10K POT in series with the input as volume control if you need.Not shown in circuit diagram. All electrolytic capacitors must be rated at least 50volts.
রবিবার, ৪ মে, ২০২৫
27MHz RECEIVER
27MHz RECEIVER The 27MHz receiver is really a transmitter. It's a very weak transmitter and delivers a low level signal to the surroundings via the antenna. When another signal (from the transmitter) comes in contact with the transmission from the receiver it creates an interference pattern that reflects down the antenna and into the first stage of the receiver. The receiver is a super-regenerative design. It is self-oscillating (or already oscillating) and makes it very sensitive to nearby signals. See full description in 27MHz Links article
5-TRANSISTOR RADIO
5-TRANSISTOR RADIO If you are not able to get the ZN414 IC, this circuit uses two transistors to take the place of the chip.
LIE DETECTOR-3
LIE DETECTOR-3 This circuit detects the resistance between your fingers to turn the 4 LEDs. As you press harder, more LEDs are illuminated
LIE DETECTOR-2
LIE DETECTOR-2 This circuit detects the resistance between your fingers to turn on the FALSE LED. The circuit sits with the TRUE LED illuminated. The 47k pot is adjusted to allow the LEDs to change state when touching the probes.
WHITE LINE FOLLOWER
WHITE LINE FOLLOWER This circuit can be used for a toy car to follow a white line. The motor is either a 3v type with gearing to steer the car or a rotary actuator or a servo motor. When equal light is detected by the photo resistors the voltage on the base of the first transistor will be mid rail and the circuit is adjusted via the 2k2 pot so the motor does not receive any voltage. When one of the LDR's receives more (or less) light, the motor is activated. And the same thing happens when the other LDR receives less or more light
SUPER EAR
SUPER EAR
This circuit is a very
sensitive 3-transistor
amplifier using a
speaker transformer.
This can be wound
on a short length of
ferrite rod as show
above or 150 turns
on a 10mH choke.
The biasing of the
middle transistor is
set for 3v supply.
The second and third
transistors are not
turned on during idle
conditions and the quiescent current is just 5mA.
The project is ideal for listening to conversations
or TV etc in another room with long leads
connecting the microphone to the amplifier.
8 MILLION GAIN!
শনিবার, ৩ মে, ২০২৫
Dome Lamp Dimmer
There are times when a little light inside the car would greatly assist one of the passengers but the dome light is too bright for safe driving. The dimmer circuit in fig. 1 may be added to an existing dome light or included with a new passenger spot lamp. The upper op-amp generates a 700 Hz sawtooth waveform which is compared to a setpoint voltage by the lower op-amp. When the sawtooth voltage is above the setpoint, the transistors turn on supplying current to the bulb. The setting of the potentiometer determines the width of the pulses sent to the lamp and therefore the average voltage. The lamp is dim when the potentiometer is set near the higher voltage. Since the TIP32 switches on and off instead of simply dropping the voltage like a power rheostat, the power it dissipates remains low and a heat sink is not necessary. Many autos run power to lamps with only one wire using the car body for the return current path so the dimmer must interrupt the positive lead as shown. Simply cut the wire leading to the lamp and connect the lamp end to the collector of the TIP32 and connect the battery end to the circuit power input. Run an additional ground wire to the auto chassis from the circuit. This ground wire will not carry much current and may be a smaller gauge.
Discrete component motor direction controller
This circuit can control a small DC motor, like the one in a tape recorder. When both the points A & B are
"HIGH" Q1 and Q2 are in saturation. Hence the bases of Q3 to Q6 are grounded. Hence Q3,Q5 are OFF and
Q4,Q6 are ON . The voltages at both the motor terminals is the same and hence the motor is OFF. Similarly
when both A and B are "LOW" the motor is OFF.
When A is HIGH and B is LOW, Q1 saturates ,Q2 is OFF. The bases of Q3 and Q4 are grounded and that of
Q4 and Q5 are HIGH. Hence Q4 and Q5 conduct making the right terminal of the motor more positive than
the left and the motor is ON. When A is LOW and B is HIGH ,the left terminal of the motor is more positive
than the right and the motor rotates in the reverse direction. I could have used only the SL/SK100s ,but
the ones I used had a very low hFE ~70 and they would enter the active region for 3V(2.9V was what I got
from the computer for a HIGH),so I had to use the BC148s . You can ditch the BC148 if you have a
SL/SK100 with a decent value of hFE ( like 150).The diodes protect the transistors from surge produced
due to the sudden reversal of the motor. The approx. cost of the circuit without the motor is around Rs.40.
Note: You can change the supply voltage depending on the motor, only thing is that it should be a 2 or 3V
more than the rated motor voltage( upto a max. of 35V).
Pulsing Third Brake Light
I'm checking into the legalities of this particular circuit at this time. Any type of flashing light on the main brake lights is prohibited and illegal in most states of the U.S.A. I'm verifying for the same here in Canada. In the mean time, use this circuit at your own risk and be aware that the possibility exists to be stopped by law enforcement if you implement this circuit in your vehicle.
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)
440
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 TO92 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 lowoutput 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 Lightuntil 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.
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:
Simple but reliable 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... ;-)
Long duration timer circuit
Description.
This timer circuit can be used to switch OFF a particular device after around 35 minutes. The circuit can be
used to switch OFF devices like radio, TV, fan, pump etc after a preset time of 35 minutes. Such a circuit
can surely save a lot of power.
The circuit is based on quad 2 input CMOS IC 4011 (U1).The resistor R1 and capacitor C1 produces the
required long time delay. When pushbutton switch S2 is pressed, capacitor C1 discharges and input of the
four NAND gates are pulled to zero. The four shorted outputs of U1 go high and activate the transistor Q1
to drive the relay. The appliance connected via the relay is switched ON. When S2 is released the C1 starts
charging and when the voltage at its positive pin becomes equal to ½ the supply voltage the outputs of
U1 becomes zero and the transistor is switched OFF. This makes the relay deactivated and the appliance
connected via the relay is turned OFF. The timer can be made to stop when required by pressing switch S1.
Repeating Timer No.2
Repeating Timer No.2 Description: This circuit is based on a simple asymmetric oscillator.
The length of time the relay remains energized - and the length of time it remains de-energized -
are set independently. With the component values shown in the diagram - both periods are adjustable from about 1 to 30 minutes.
Setting The Timer: The frequency of the Astable Oscillator depends on the value of C1 and the speed at which it charges and discharges through the resistor network. The length of time the relay remains energized is controlled by R2.And the length of the time it remains de-energized is controlled by R3.
Owing to manufacturing tolerances - the precise length of the time periods available depends on the characteristics of the actual components you've used. R1 & R4 set the minimum period lengths at about 1 minute - while R2 & R3 set the maximum periods at about 30-minutes.
You can choose component values that suit your own requirements. If your time periods don't need to be too precise - and more-or-less is close enough - you can leave out the pots altogether - and simply rely on R1 & R4 to set the times. 421 Alternative Capacitor:
A regular electrolytic capacitor is polarised. If the charge on its plates is the wrong way round - DC current will flow through the capacitor. If the current is high enough - the capacitor will heat up and explode. When the oscillator is running - the polarity of the charge on C1 keeps reversing. So C1 needs to be non polarised. However - you can simulate a non-polarised 470uF capacitor by connecting two 1000uF
polarised capacitors back to back - as shown. How and why this works is explained in the Detailed Circuit Description. Because non-polarised capacitors aren't widely available - the prototype was built using two polarised capacitors. Do not use the "on-board" relay to switch mains voltage. The board's layout does not offer sufficient isolation between the relay contacts and the low-voltage components. If you want to switch mains voltage - mount a suitably rated relay somewhere safe - Away From The Board you can use a multi-pole relay if you wish
The timer is designed for a 12-volt power supply. However - it will work at anything from 5 to 15-volts. All you need do is select a relay to suit your supply voltage. The Cmos gates are being used as simple inverters. So - although I've used a Cmos 4093 in the circuit diagram - a Cmos 4001 or Cmos 4011 will work just as well
