I want to build a small circuit that will switch a LED on (for arguments sakes) when the cars ignition gets switched on. But I want to make it versatile so I can work with between 12V - 36V (Cars, Trucks, etc). What would be the best to read the Ignition status via the arduino. Know I have thought of an idea by working with voltage divider. Basically taking the principal of reading voltage Instructable Example and working from there. Any thoughts?

  • An Arduino seems a bit of overkill to just light an LED when the power is turned on...
    – Majenko
    Apr 18, 2016 at 20:41
  • Hi Majenko. My circuit will do more then just switch an LED on. Like I said (for arguments sake) I actually want to do a Vehicle Tracking unit but I must be able to to handle all voltage inputs between 12V - 36V
    – Dev Expert
    Apr 20, 2016 at 6:24

2 Answers 2


Even easier:

  • input - series 220 ohm resistor, and a 78L05 voltage regulator (check for maximum voltage). This allows you handling like 4..30V and get a solid "1" on digitalRead. (4V input makes like 3V output which is still logic high).
  • HAHAHA Gee Bee its you again. You always seem to come to my rescue. Tell me would something like this work 7805 SMD
    – Dev Expert
    Apr 20, 2016 at 6:27
  • Sure, it works up to 35V input out of the box, no series resistor. LM317HV works for much higher input voltage (you need two resistors to set up the output to 4.5Vish to get a stable 1 level). These solutions are clear overkills - you could do this with series resistors, zeners, NPN transistor, etc. - but a voltage regulator is only one component to solder.
    – Gee Bee
    Apr 20, 2016 at 12:31

you can use transistor bias circuit, opto-couples circuits, op amp circuit or a simple relay circuit, to get 5V output signal when 12V-36V signal is triggered.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.