Using external ground for low input

Other Hardware General Electronics
1

Hi all,

I am trying to control car windows with an Arduino. The car came with manual windows. From the car door, I want to send a low signal to an input on the Arduino that will have the internal pull up turned on. Is it Ok to use the ground from the car door (which essentially goes to the car battery) to signal the Arduino?

Do I have tie in the ground on the Arduino to the ground on the car battery?

Thanks

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2

I suspect that the battery ground and the 5V ground are already tied together through the DC-DC converter. Can you check that?

3

tmd3:
I suspect that the battery ground and the 5V ground are already tied together through the DC-DC converter. Can you check that?

I do not have the parts in just yet. I wanted to make sure my wiring will be sound.

I was originally thinking about using a 12V signal and making it so that Arduino can take it. But if I can just use ground, it will make this a lot simpler.

Thanks

4

Much simpler to use ground but you still need the same protection on the inputs. If a careless mistake can accidentally brush a 12V wire across your Arduino input wire, then you must put protection on that input. Often just a series resistor will be good enough.

5

The electrical environment in a car can be particularly challenging. If you're designing for automotive use, you may want to consider protecting your circuitry from transient voltages.

Here's a paper from Littelfuse describing the kinds of things that can happen on the supply lines. The paper is written around US practices for auto power systems. It's dated 1999. Things may have gotten better in the intervening 17 years, to accommodate new electronic systems. The basic technology, though - a belt-driven alternator charging the battery - hasn't changed much.