user19724: 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?

user19152: 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).


19724: <p>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 <a href="http://www.instructables.com/id/Arduino-Reading-Analog-Voltage/" rel="nofollow">Instructable Example</a> and working from there. Any thoughts?</p>
 19152: <p>Even easier: </p>

<ul>
<li>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).</li>
</ul>
