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I need a help with this question. I'm trying to make a Wheatstone Bridge with Arduino, the main idea is read the two legs of the circuit with two analog inputs of Arduino, for the while I'm analyzing the values with 4 equal resistors as the Arduino reads (0 to 1023 bits). The problem is when I change one of the resistors (Rx), the voltage on A0 (first leg C) should not be changed, but it happens.

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I've read something about the analog inputs of the Arduino suffer interference, but I don't know how to avoid this.

Edgar Bonet
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    You can try taking the reading twice and discarding the first one. However, if you want precision, rather than subtracting two single-ended readings, you should take one differential reading. The ACD of the Mega has this capability, with up to 200× gain. – Edgar Bonet Jun 04 '15 at 09:02
  • @EdgarBonet - are you referring to the Analog Comparator here? – Nick Gammon Aug 24 '15 at 06:48
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    @NickGammon: No, I am referring to the ADC of the ATmega2560, which can operate in differential mode. – Edgar Bonet Aug 24 '15 at 19:36
  • It could change in reality, if your excitation supply isn't stable. Edgar Bonet's suggestion of differential ADC is a good one. See page 283 of the datasheet at http://www.atmel.com/Images/Atmel-2549-8-bit-AVR-Microcontroller-ATmega640-1280-1281-2560-2561_datasheet.pdf – Dave X Nov 18 '15 at 22:55

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