Simple Car Headlight Timer Circuit using Transistors

Simple Car Headlight Timer Circuit using Transistors is cool design.

It keeps car headlights ON for 1.5 minutes after engine is OFF.

It is very useful in dark place which gives light for short time.

Circuit uses easy parts like transistors, resistors, capacitor, relay and few more.

These all work together for timing.

This article shows how it works, gives design formulas and few easy steps to build it.

Circuit Working:

Parts List:

When push button is pressed capacitor C1 start charging through resistor R1.

This makes voltage on C1 which turns ON the transistor Q1.

Q1 ON sends current to base of Q2 BC327.

Q2 ON powers relay coil.

Relay closes and 12V battery sends power to headlight and headlight turns ON.

Same time C1 slowly discharges through resistor R2 and voltage at Q1 base goes down.

When voltage is too low then Q1 and Q2 turns OFF with relay and headlight OFF.

Diode D1 across relay coil stops voltage spikes when relay turns OFF.

Warning: Be very careful connecting to car because wrong wiring can damage car and may cost big money.

Formula:

Formula for Simple Car Headlight Timer Circuit using Transistors:

RC Time Constant:

Timer depends on R1 and C1 values.

To find discharge time (t) use formula:

t = R × C

where:

• t is the time in seconds
• R is the resistance in ohms
• C is the capacitance in farads

How to Build:

To build a Simple Car Headlight Timer Circuit using Transistors follow the below mentioned steps for connections:

• Connect base of Q1 to one end of R1.
• Other end of R1 goes between one end of push button and positive side of C1
• Connect negative side of C1 to GND.
• Other end of push button goes to +12V.
• Connect collector of Q1 to base of Q2.
• Connect emitter of Q1 to GND through R3.
• Connect one end of R2 between collector of Q1 and base of Q2.
• Other end of R2 goes to emitter of Q2.
• Connect collector of Q2 to D1 and GND.
• Place diode D1 across relay coil pins to stop voltage spikes
• One pin of relay coil goes to +12V
• Other pin goes to collector of Q2
• Connect COM pin of relay to +12V battery.
• Connect NO pin to car headlight.
• Headlight GND wire goes to ground.

Conclusion:

This Simple Car Headlight Timer Circuit using Transistors is easy and useful.

It keeps headlights ON for some time after car engine is OFF.

We can change timer by changing resistor and capacitor.

It is a good project to learn how transistors control relays in circuits.

References:

Headlight modulator circuit design