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Topic: [Solved]Read voltage across a resistor and use it as an input to an anlog pin. (Read 1 time) previous topic - next topic


Feb 19, 2011, 06:36 am Last Edit: Feb 19, 2011, 06:43 am by CrossRoads Reason: 1
Sounds like you are getting the hang  of it!

Yes, the arduino ground connects to the ground of what you are measuring. If that is a single supply op amp than that is what you  connect to.
For example, an op amp like this, which runs from +5v and Gnd.

The arduino running on batteries is like a portable multimeter - you are measuring the red lead (Analog in) with respect to the black lead (arduino ground).
Only the arduino can't withstand negative voltage, while the multimeter can - so the black lead must be connected to the circuits ground and only positive measurements can be made.
If you have an op amp with +/- supplies, then you must be careful - perhaps adding a diode before the analog input pin to rectify the incoming voltage, at the loss of voltage drop across the diode.

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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