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Using Single Switch for Fog lamp and DRL Lamp

The post explains an easy method of upgrading your existing car fog lamp switch such that it allows toggling both the fog lamp as well as the DRL lamps alternately, as per the owner's requirement. The idea was requested by mk karthick.

Circuit Objectives

  1. Am looking for a circuit which is directly connected to the fog lamp output from car dashboard. The circuit will control Fog and DRL lamps together with single switch, and do switching to my response without modifying the old switches in my vehicle.
  2. Car-Fog light when switched one time ON and OFF, will switch ON the fog light continuously,
    Car-Fog light when switch two times ON and OFF the fog light is supposed to go off and DRL LED illuminate and stay ON continuously.
  3. I want to reduce extra control switches & cable loops inside my car. Please help me a with a suitable circuit design. thanks in advance.

The Design

The proposed single switch fog light and DRL light can be witnessed below. It uses a single IC 4017 for the required operations. The IC 4017 is used for sequentially changing the switching operation through a single input toggling, thereby allowing two different lamps to be operated using a single existing car dashboard switch

How it Works

The main purpose of this DRL and Fog light changeover circuit is to allow a single switch operation for selecting the fog light and the DRL light in tandem, without having to depend on any other external switching arrangement.

Here when the fog switch is first turned ON and OFF, the fog light is switched ON. On a subsequent ON and OFF of the fog switch, switches OFF the fog light and turns ON the DRL lamp, on further toggling, the fog light yet again switches ON extinguishing the DRL.

In order to reset the system, the fog light switch could be held in the ON position for a couple of seconds. This will reset the whole circuit so that a fresh cycle could be initiated, although this may be never be necessary, since just a couple of simple operations are involved in the system.

It must be noted though, that the selected lights will be flipped-over and continue to remain ON, only while the fog switch is in OFF position. Keeping it ON will switch OFF the circuit and the lamps permanently.

Parts List

Resistors are all 1/4 watt 5%

10K - 6nos

100K - 1no

Capacitors, 1uF/25V, 10uF/25V, 100uF/25V - 1 no each

Diode 1N4007 - 2nos


BC547, BC557 - 1 each

TIP122 - 2nos

IC 4017 - 1no



About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

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