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Topic: Is arduino equiped with AC protection? (Read 1 time) previous topic - next topic


I have an input coming from a car. It goes from 0V to roughly 18V at max. I was hoping to build a simple voltage divider using about 500k and 2M (arduino seeing the voltage across the 500k which is about 3.7V at max which would be plenty for analog reading). But there is one problem. There is roughly 25V of AC riding on that DC and I don't know what frequency. All I have is a basic multimeter. What should I do? Should I block the AC or use a diode somehow or does the arduino have something built in that can help me with this?

Thanks! (:

I tried to find a schematic of the arduino UNO or MEGA (I HAVE BOTH) but it looks like this site is down?


If you have just a 1M resistor you could get away with using the internal protection diodes and directly hook it up to your source, now this is just technically and no one really like to do this, your best off with using external clipping diodes to protect from >5v and <0v
There will also be resistors involved and the values and wattage of the external diodes will vary depending on your needed frequency response


You can't measure anything till you get rid of AC.  Simple RC is the easiest way. Resistor limiting current below 1 mA , and you o'k with internal diodes build in AVR chips.
Only 1M too much, analog reading requirement < 50 k. Even with 20 k in voltage divider it save to overvoltage input up to : V = R * I + 5V = 20k * 1 mA + 5V = 25V


Dec 30, 2012, 09:05 pm Last Edit: Dec 30, 2012, 09:08 pm by durkinnj Reason: 1
Not sure if I completely understand either of you. 1M not 1M diodes not diodes. What should I do? Are you saying limiting the current bellow 1mA will be good enough to run the source straight into the arduino using a voltage divider? And you are saying that 1M is limiting it too much? So I should use like a 5k and a 20k for the volatge divider?


Dec 30, 2012, 09:08 pm Last Edit: Dec 30, 2012, 09:30 pm by JimboZA Reason: 1
Forgive my ignorance, but what does it mean for 18VDC to have 25VAC riding on it?
Roy from ITCrowd: Have you tried turning it off an on again?
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