# 12v 2 input or gate circuit

#### Craig Robertson

Joined Aug 22, 2017
3
Hi,

New here so hi to everyone!!

I have installed footwell lights that come on with the headlights. I also want them to come on with the interior lights when the doors open.

To do this I know I need an or gate to control the 2 12v input to have the lights turn on.

Any help would be great!!

Thanks,
Craig.

#### AlbertHall

Joined Jun 4, 2014
11,217
The CD4001 is a quad 2-input OR gate with a maximum supply voltage of 15V, but a car battery being charged comes perilously close to that.
Maybe you could use something like the circuits below:

#### Craig Robertson

Joined Aug 22, 2017
3
Thanks for the information on using diodes or transistors as it's a 12v circuit. What would be the best way to make and package the circuit up?

#### crutschow

Joined Mar 14, 2008
26,977
The CD4001 is a quad 2-input OR gate with a maximum supply voltage of 15V, but a car battery being charged comes perilously close to that.
Maybe you could use something like the circuits below:
The opposite transistor Vbe reverse voltage will be exceeded when one of the transistors turns on so you would need to add a diode in series with each base input to prevent zapping the transistor.

Likely the two diode circuit is a better and easier way to do what you need.

#### AlbertHall

Joined Jun 4, 2014
11,217
The opposite transistor Vbe reverse voltage will be exceeded when one of the transistors turns on so you would need to add a diode in series with each base input to prevent zapping the transistor.

Likely the two diode circuit is a better and easier way to do what you need.
Yes, of course, because we have a 12V to 15V supply voltage.

#### Bordodynov

Joined May 20, 2015
2,834
Use 2SD2704K.

#### AnalogKid

Joined Aug 1, 2013
9,165
What powers the footwell lights now? Are they simply connected straight to the headlights power? If so, is it your intent to have them powered directly from wither the headlights or dome lights, or is there a relay driving the footwell lights and you want to control the relay? Also, what is the current needed by the footwell lights?

ak

#### Craig Robertson

Joined Aug 22, 2017
3
Hi sorry I have been on holiday.

Thanks for all the replies!!

At the moment they are connected to and powered by the interior lighting circuit that comes on when the headlights are either switched on manually or on the auto setting. That is the first input, I want you also add the dome light circuit, so they will also come on when the doors unlock/open.

#### AnalogKid

Joined Aug 1, 2013
9,165