eCircuitbook

Transmitter Parts:

R1, R4, R6 10K resistor


R2 1Meg resistor


R3 100K resistor


R5 100 ohm resistor


R7 1K resistor


C1, C2 0.1uf capacitor


C3 0.01uf capacitor


C4 4-40pf variable capacitor


C5 4.7pf capacitor


Q1, Q2 2N3904 transistor


L1 8-10 turns of 22gauge wire around non-conductive 1/4" diameter form


Elec Mike Electret Mic

Parts List:

R1,R3 = 100K


R2 = 10K


R4 = 470 ohm


C1,C4 = 470pF


C2,C3 = 4.7µF, 16V, electrolytic


C5,C6 = 4.7pF


C7 = 4-40pF trimmer cap (optional, see text)


L1 = 1µH


Q1,Q2 = 2N2222, NPN transistor


Mic = Electret Microphone


B1 = 9 Volt, Alkaline battery

This unique circuit makes your dome light look cool. Usually when the car door is closed, the dome light just goes OFF. With this circuit, you can have our dome light fade slowly in brightness and finally go OFF. This slow dimming of the light gives a very good feeling at night. It looks very romantic!

A continuously working wiper in a car may prove to be a nuisance, especially when it is not raining heavily. By using the circuit described here one can vary sweeping rate of the wiper from once a second to once in ten seconds. The circuit comprises two timer NE555 ICs, one CD4017 decade counter, one TIP32 driver transistor, a 2N3055 power transistor (or TIP3055) and a few other discrete components. Timer IC1 is configured as a mono- stable multivibrator which produces a pulse when one presses switch S1 momentarily. This pulse acts as a clock pulse for the decade counter (IC2) which advances by one count on each successive clock pulse or the push of switch S1. Ten presets (VR1 through VR10), set for different values by trial and error, are used at the ten outputs of IC2. But since only one output of IC2 is high at a time, only one preset (at selected output) effectively comes in series with timing resistors R4 and R5 connected in the circuit of timer IC3 which functions in astable mode. As presets VR1 through VR10 are set for different values, different time periods (or frequencies) for astable multivibrator IC3 can be selected. The output of IC3 is applied to pnp driver transistor T1 (TIP32) for driving the final power transistor T2 (2N3055) which in turn drives the wiper motor at the selected sweep speed. The power supply for the wiper motor as well as the circuit is tapped from the vehicle�s battery itself. The duration of monostable multivibrator IC1 is set for a nearly one second period

A battery is a vital element of any battery-backed system. In many cases the battery is more expensive than the system it is backing up. Hence we need to adopt all practical measures to conserve battery life.


As per manufacturer's data sheets, a 12V rechargeable lead-acid battery should be operated within 10. IV and 13.8V.