# Sharing a button with another controller that reads 12V signals.

For a vehicle simulator project, I want to use an Arduino to read input from an existing light switch in a (unpowered) car. At the same time, a collaborator who is preparing the car itself, would like the button to send a 12V signal to be read by the existing light-controller which in turn activates the real car lights.

Other than having completed the very basic Arduino tutorials, I’m an absolute beginner in electronics in general. I’ve attached a naive diagram of the situation, which would probably fry the arduino. So my two specifiq question to this situation are:

Question 1: is it reasonable to power the Adruino with a 12V power supply and use VIN pin as a source for the 12V signal?

Question 2: what are ways to convert the 12V signal to a safe 5V signal for the Arduino? Or would it make more sense to somehow stretch a 5V signal on the way to the light controller?

It would be great if you could help me on how to approach this. Thanks!

aaronateo:
Question 1: is it reasonable to power the Arduino with a 12V power supply and use Vin pin as a source for the 12V signal?

No, Certainly not in a car. Use a switchmode "buck" converter rated up to at least 30 V to provide 5 V regulated power to feed in the "5V" pin.

aaronateo:
Question 2: what are ways to convert the 12V signal to a safe 5V signal for the Arduino?

Thank you! I will investigate into buck converters and will probably try it out with a small prototype soon.
As far as I understand, your diagram shows a voltage divider and is not using a buck converter, right?
And for the input I need to think of another power source than the Arduino to get the 12V signal?

To derive a "12 V signal" from the Arduino, you need one or two transistors. Nowadays, the proper "transistors" are MOSFETs (which are the basis of all current computer components), there is little reason to use bipolar transistors.

But you must define what 12 V "signal" you require - does it need to pull 12 V down to ground (dead easy), to pull up to 12 V (more tedious) or switch between ground and 12 V (comparatively more tedious again ) and in each case, how much current must it switch?

Actually, you really need to characterise what your "collaborator" specifically needs, what the existing light-controller actually is and whether (s)he does need 12 V rather than something else?

Suggest the OP use:

1. an optoisolator

2. a transistor switch.

Sorry, I was away for a few days.

Thanks to both of you!

I will try to get more information on the kind of 12V signal and light-controller my collaborator needs.
And the suggested components are a nice starting point to build a prototype to test.