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I've created this small circuit to translate voltage drop over a shunt resistor into a usable range for arduino (5v atmega32u4) adc.

This is to measure current out of and into (charging) a 12v battery on a boat. The shunt is low side (connected to Bat-). My circuit has Bat- as Ground, Vin at high side of shunt. The shunt is 75mV at 100A.

The circuit seems to work nicely (though center was ~0.8v below the expected 2.5?)

Question(s): It should probably be some form of protection in there. If I float Vin, output goes >9v and uC-pins would be unhappy. Is a zener diode enough?

Anything else that's missing? 0.1u caps on input and output?

schematic

simulate this circuit – Schematic created using CircuitLab

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    \$\begingroup\$ Don't add a capacitor on an opamp output. You may add a clamp (zener or schottky to 5v) and a series resistor. \$\endgroup\$
    – Mike
    Commented Jun 2, 2017 at 21:38
  • \$\begingroup\$ I'm not sure I understand your question I would power your opamp off a wide input range LDO, even a 7805 would do, versus directly powering on VBAT \$\endgroup\$
    – sstobbe
    Commented Jun 2, 2017 at 21:44
  • \$\begingroup\$ @sstobbe: I'm sorry, what's unclear? I'd like to know how I should prevent the ~12v op-amp circuit from blowing up the 5v uC pins if it gets out of control. I was thinking about regulating 12v, but figured I would try to compensate for the varying voltage in software (I'm measuring the battery voltage separately) \$\endgroup\$
    – ttyridal
    Commented Jun 2, 2017 at 21:50
  • \$\begingroup\$ Where's the current shunt in your circuit. \$\endgroup\$
    – Andy aka
    Commented Jun 2, 2017 at 21:50
  • \$\begingroup\$ The Sine generator in the schematic will be the current shunt. \$\endgroup\$
    – ttyridal
    Commented Jun 2, 2017 at 21:53

1 Answer 1

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A zener clamp will be sufficient to protect the uP A/D input.

If the measured parameter is an AC signal, capacitors would only remove DC bias. The resulting AC signal or spikes could still exceed the input ratings.

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