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I am working with an Arduino Nano multimeter. The multimeter has an internal resistance of approximately 14 MΩ. When the probes aren't connected to anything I don't get 0 V. When they are connected to a resistor with a resistance of 40 Ω, it measures 0 V, with a resistance of 10 MΩ I don't get 0 V once again. What could be the reason for this?

Also, the probes are connected to input pins A0 and A1. Are these pins connected to ground through the inner circuitry since the multimeter can in fact read some value even though the resistor isn't connected to ground?

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    \$\begingroup\$ "Also, the probes are connected to input pins A0 and A1." I'd expect them to be connected to A0 and GND. Add the schematic into your question. \$\endgroup\$
    – Transistor
    Sep 20, 2022 at 16:45
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    \$\begingroup\$ Could you edit your question with the following: a schematic or a link to the design you've implemented, and where you say you're not seeing 0V, say what you are seeing. Note that voltmeters are pretty specialized instruments, and there's a big tradeoff between easy to make and working exactly right -- you're probably experiencing that. \$\endgroup\$
    – TimWescott
    Sep 20, 2022 at 17:24
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    \$\begingroup\$ is it really a multimeter? ... do you measure anything other than voltage? \$\endgroup\$
    – jsotola
    Sep 20, 2022 at 17:36

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When the probes aren't connected to anything I don't get 0V. What could be the reason for this?

You probably wont, the probes will pick up noise and float to different voltages than 0V.

When they are connected to a resistor with resistance 40 ohms, it measures 0V, with a resistance 10 Mega Ohms I don't get 0V once again.

The nodes will be floating again, there is an input bias current on the ADC/Analog that is probably in the mA to uA range. A 10meg resistor would 1V/10MegΩ would be 0.1uA, that amount of current is difficult to measure and requires good equipment.

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    \$\begingroup\$ 1V/10M\$\Omega\$ is 0.1\$\mu\$A, isn't it? \$\endgroup\$ Sep 20, 2022 at 16:31
  • \$\begingroup\$ Yeah, Good catch \$\endgroup\$
    – Voltage Spike
    Sep 20, 2022 at 20:06

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