A simple headlight timer circuit is a cool electronic setup that keeps a cars headlights on for 1.5 minutes even after the engine is turned off.
This is super helpful when you park in dark areas because it lights up your way for a short time.
The circuit is made up of simple parts like transistors, resistors a capacitor a relay and some other basic components that all work together to make the timing happen.
In this article we will look at how the circuit works, by going with formulas needed for the design and explain how to build it step by step.
Circuit Working:
Parts List:
| Component | Specification | Quantity |
|---|---|---|
| Resistor | 1k 1/4 watt | 2 |
| Resistor | 4.7k 1/4 watt | 1 |
| Capacitor | Electrolytic 100μF 25V | 1 |
| Transistor | BC547 | 1 |
| Transistor | BC327 | 1 |
| Diode | 1N4007 | 1 |
| Push Button Switch | – | 1 |
| Relay | SPSDT | 1 |
When the button switch called is pressed the capacitor named C1 starts to charge up through a resistor R1.
This charging creates a voltage across C1 which then turns on the base of the transistor Q1.
With Q1 activated it allows current to flow into the base of another transistor Q2 which is a BC327.
When Q2 is turned on it powers the relay coil.
This action closes the relay contacts, allowing current to flow from the 12V battery to the car headlight making it light up.
At the same time C1 begins to discharge slowly through the resistor R2 which lowers the voltage at the base of Q1.
When this voltage drops below a certain level both Q1 and Q2 stop working.
As a result the relay loses power and the headlight turns off.
To protect the circuit from any voltage spikes that might happen when the relay is turned off a diode D1 is placed across the relay coil.
Note: You need to be super careful when connecting this circuit to your car because if you make a mistake it could end up costing you a lot of money.
Formula:
Formula is mentioned below for Simple Car Headlight Timer Circuit using Transistors
RC time constant:
The timing of the circuit mainly relies on the values of R1 and C1.
You can estimate the discharge time (t) by using the RC time constant 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:
- Gather all the components mentioned in the above mentioned circuit diagram.
- Connect the base of transistor Q1 to one end of R1 resistor and other end of R1 between one end of push button switch and the other end of switch and positive of capacitor C1 and negative of C1 to GND.
- Connect the collector of transistor Q1 to base of transistor Q2.
- Connect the emitter of transistor Q1 to GND through resistor R3.
- Connect one end of resistor R2 between collector of transistor Q1 and base of transistor Q2 and the other end to emitter of transistor Q2.
- Connect the collector of transistor Q2 to diode D1 and GND.
- Connect a diode D1 to one pin of 12V relay coil and the other end pin of relay coil to GND, COM pin of 12V relay to +12V car battery, NO pin of 12V relay to car headlight.
Conclusion:
This simple car headlight timer circuit using transistors is an easy and useful design that makes driving safer and more convenient.
It uses simple electronic parts to help keep the headlights on longer.
You can easily change how long the lights stay on by adjusting the resistor and capacitor values to fit what you like.
This project is a great way to see how transistors can control relays and create different functions in electronics.