ESR meter with Arduino

Projects Discussion and Showcase Science and Measurement
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  1. You cannot measure capacitance in-circuit.

  2. You can measure ESR, close enough for troubleshooting, in most circuits.

The key is to keep the sensing voltage below the peak voltage that could turn a semiconductor junction on, including Shottky.

  1. You cannot use the same method to measure ESR and ESL over a really wide range of capacitance.

But it doesn't really matter. Mostly it is electrolytic capacitors that fail by increasing ESR. And the values that matter are >=1uF, usually much larger.

ESR of a few ohms doesn't really matter for audio coupling capacitors, which are normally around 1uF to 10uF. For linear power supplies, ESR of a few ohms matters, but the capacitors are generally in the range of thousands of uF. For switching power supplies, ESR needs to be tenths of an ohm, but capacitance is still >>10uF.

And all those capacitors have varying amounts of parasitic inductance. But that doesn't change, so no real need to measure it. That is why a circuit will have Vcc bypassed by (in addition to the 100s or 1000s of uF of smoothing capacitor) both a 1uF and 1nF bypass capacitor.

For capacitors in the nF range, there are not really many mechanisms for ESR to increase as a failure mode. You can measure ESR as a function of circuit Q.