BOOK LIGHT

 This circuit keeps the globe illuminated for a few seconds after the switch is pressed. There is one minor fault in the circuit. The 10k should be increased to 100k to increase the "ON" time. The photo shows the circuit built with surface-mount components:
 

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.

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!

 

8 MILLION GAIN! This circuit is so sensitive it will detect "mains hum." Simply move it across any wall and it will detect where the mains cable is located. It has a gain of about 200 x 200 x 200 = 8,000,000 and will also detect static electricity and the presence of your hand without any direct contact. You will be amazed what it detects! There is static electricity EVERYWHERE! The input of this circuit is classified as very high impedance. Here is a photo of the circuit, produced by a constructor, where he claimed he detected "ghosts

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.