Car Head Lights Turn Off

This circuit when setup in a car automatically turns off the head light after a preset time after the ignition switch is turned off.So you can walk out easily from the dark garage in the light of your car.

Circuit diagram :

Car Head Lights Turn Off  Circuit Diagram

When the ignition switched on first the voltage from battery is fed to the relay through diode D1.When the ignition switch is turned off it produces a negative going pulse at the pin 2 that triggers the timer. The output of the IC goes high for the time set by R1  .This makes the transistor Q1 to conduct to energize the relay to drive the headlight.After the set time the light goes off.With the value of components used you can make a setting from 10 S to 60 S.
Notes :

• Assemble the circuit on a good quality PCB or common board.
• Fit the potentiometer on somewhere on the dashboard so that  you can easily set the timing.
  

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Simple B C with Automatic Switch off Circuit Diagram

This is a Simple Battery Charger with Automatic Switch-off Circuit Diagram. This lovely charger automatically switches off when your rechargeable batteries reach the full charge.The circuit comprises a bistable multivibrator wired around timer IC 555. The bistable output is fed to an ammeter (via diode D1) and pot meter VR1 before it goes to three Ni-Cd batteries that are to be charged.

Battery Charger with Automatic Switch-off Circuit Diagram

Normally, the full charge potential of an Ni-Cd cell is 1.2V. Trigger the bistable by pressing switch S1 and adjust potmeter VR1 for 60mA current through the ammeter.

Now remove the ammeter and connect a jumper wire between its points ‘a’ and ‘b.’ Connect the positive output terminal of the batteries to the emitter of pnp transistor T1. The base of transistor T1 is held at 2.9V by adjusting potmeter VR2. The output of transistor T1 is inverted twice by npn transistors T2 and T3.

Thus when the batteries are fully charged to 3×1.2V=3.6V, a voltage higher than this makes transistor T1 to conduct. Transistor T2 also conducts and transistor T3 goes off. The threshold level of timer 555 reaches 6V, which is more than 2/3×VCC = 2/ 3×6=4V, to turn off the timer.

During charging, the threshold level of the timer is held low. The green LED (LED1) glows during charging of the batteries and goes off at the attainment of full charge.

Note that this circuit can be used only for 1.2V, 600mAH Ni-Cd rechargeable batteries that require 60 mA of current for 15 hours to charge fully.

Author : V. Gopalakrishnan

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