I am working on a simple Arduino capacitance meter.

This project uses twp resistors: a 10 kohms resistor for charging and 220 ohms resistor for discharging.

The Arduino is programmed to measure the time constant T=RC and eventually calculate the capacitance.

Now for large capacitors such as a 3900 uf capacitor, the time between the readings took several minutes.

I was wondering if we can fix that buy changing the charging resistor(10 kohms) with a small resistor say 220 ohms or something.

  • 1
    \$\begingroup\$ Ohm's law will give you the initial current. With a voltage of 5V you get 5V / 220 Ohm = 22.7 mA. So the resistor needs a minimum Watt rating of 5V * 22.7mA = 113.5 mW. Though this is off topic here, since it's about electronics and not Arduino. \$\endgroup\$
    – chrisl
    Dec 8, 2018 at 9:56

1 Answer 1


This question has not much to do with Arduino, but yes, you can. You only have to take into account the maximum amount of current that will flow. This current occurs when you start charging the capacitor and (as you will know) is V/R (where of course V is the supply voltage). The power supply, the resistor and the capacitor have to be able to handle this current (but only for a small time period).


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