Headlight 'On' warning buzzer ...

Ever left your lights on, and come back to a car with a flat battery. Most modern cars come with a small electronic circuit that will warn you that the lights have been left on. Why not have the same setup in your Suzuki SJ. Here is a simple circuit that can be easily built to warn you via an audio buzzer that you have forgotten to switch off the vehicle headlights.

Components ...

-2N2222 Transistors (qty 2).
-10 Kilo ohm resistors (qty 3).
-4.7 Kilo ohm resistor (qty 1).
-220 ohm resistor (qty 1).
-1N914 Diode (qty 1).
-LED (qty 1).
-Piezo buzzer (qty 1).
-LED holder.
-Perf board or component board.
-Heat shrink wrap.
-24"Black/Blue wire (Black wire with Blue stripe).
-24"Green/Red wire (Green wire with Red stripe).
-24"Black wire.

Assembly ...

The base of transistor Q1 is connected to the car's ignition circuit, and the one side of the piezoelectric buzzer is connected to the instrument-panel light fuse (when the headlights are on, the instrument panel is illuminated). When the headlights are off, no current reaches the buzzer and therefore nothing happens. What happens when the headlights are on depends on the state of the ignition switch. When the ignition is on, transistors Q1 and Q2 are biased on, effectively removing the buzzer and the LED from circuit.

When the ignition switch is turned off but the headlights are on, transistor Q1 is turned off, but transistor Q2 continues to be biased on. The result is that the voltage across the piezoelectric buzzer and the LED is sufficient to cause the buzzer to sound loudly and the LED to light. Turning off the headlight switch will silence the buzzer.



Assemble all the components on the perf-board, or component board. The buzzer is a PC-board mount type, but almost any similar buzzer will do. Circuit parameters are not critical on this project, however, make sure that the 24"Black/Blue wire is used for the ignition switch connection wire, and that the 24"Green/Red wire is used for the wire that will eventually be connected to the fused side of the instrument panel lights.

Once assembly is complete, cut off the excess circuit board, to make a compact unit. If possible use a 12V source to test the unit to ensure it works correctly. Fit the shrink wrap over the circuit board, and gently heat it to shrink and insulate the circuit board. It is now ready to be secured into the vehicle.

Installation ...

When your are finished, house the circuit in a small, plastic experimenter's box or a plastic film container. Mount the unit securely under the dash. If you want to see the LED, then run the LED wires to where you want it mounted, drill a hole in the dash, and mount the LED. An ideal place for this is next to the headlight switch on the dash.

Only three connections are required to complete the installation. All these wires can be found under the instrument panel. Find the wire that provides power to the instrument panel (should be a Green/Red wire) and join the Green/Red wire from the unit to it. Next find the ignition wire, which should be a Black/Blue wire, and connect the Black/Blue wire from your unit to it. Now connect the Black wire to a good earth point and test the unit.