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I'd like to measure the voltage at a test point on a stepper motor driver chip with an arduino. The voltage at this point controls the amperages to the phase coils and is adjusted to trim the driver.

I have a common ground with the driver already, I'd like to wire the drivers v-ref point to an analog input to drive an LCD showing the output amp number so I can adjust the driver.

The issue I am worried about is that with the hardware I have to test with a properly trimmed driver is pushing 0.84A.

Is this safe to do without killing the arduino board?

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Yes. The only thing you need to be concerned about is the voltage. It needs to be less than the Arduino Vcc.

The voltage sense circuit (analog inputs) typically have a high impedance and should draw a negligible current from the circuit being sensed. I didn't have much luck finding the actual spec for any of the AVR chips, but I did find this answer to the question on Electronics.StackExchange – where they say "hard to tell, the specs are incomplete, but 10 KΩ seems like a reasonable guesstimate/assumption" (I paraphrase). The reasoning is interesting and worth a read.

  • Awesome thank you, I'll give it a try tonight. – asawyer Dec 28 '15 at 16:11

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