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capmeter

Capacitance, ESR, and leakage current measurements with Arduino

[- Capacitor Measurement Menu -]
1) Measure capacitance
2) Measure ESR
3) Measure leakage current
4) Charge capacitor
5) Discharge capacitor
Enter your choice: 
1
Capacitor discharged.
Measuring capacitance...
1 ms    99 nanoFarads
Discharging capacitor...
Capacitor discharged.

Algorithm

  1. Capacitance Measurement:
    • Charge the capacitor through a known resistor. (10k)
    • Measure the time taken to reach 63.2% of the supply voltage.
    • elapsedTime is measured in milliseconds and we want capacitance in microfarads (µF), we multiply by 1000 to convert: C (µF) = (elapsedTime / R) * 1000
  2. ESR Measurement:
    • Charge the capacitor through a known series resistor.
    • Measure the voltage drop across the resistor to calculate ESR.
    • This is very inaccurate. Learn more about Equivalent Series Resistance here: All About Circuits - Determining Equivalent Series Resistance (ESR) of Capacitors
    • The method we use measures the voltage drop across the resistor in a DC circuit. ESR is inherently an AC parameter, meaning it affects the capacitor's performance under alternating current conditions. Measuring ESR accurately usually requires applying a small AC signal and measuring the impedance. Plus arduino ADC does not have fine enough resolution to accurately measure the small voltage drops associated with low ESR values, especially when dealing with ceramic capacitors which can have ESR in the milliohm range.
  3. Leakage Current Measurement:
    • Charge the capacitor to a known voltage.
    • Measure the current flowing through the capacitor over time.
    • Again, the low resolution of the arduino ADC would not yield an accurate result.
  4. Charge the Capacitor:
    • Manually charge the capacitor.
  5. Discharge the Capacitor:
    • Optionally discharge the capacitor for the next measurement.

Wiring Setup

  • Capacitor: Connect between the common point and ground (positive side of an electrolytic capacitor to common).
  • Charging Resistor: Connect a known resistor (e.g., 10kΩ) between chargePin (digital pin 13) and the common point.
  • Discharging Resistor: Connect a 220Ω resistor between dischargePin (digital pin 11) and the common point.
  • Analog Pin: Connect a wire between the common point and analogPin (analog pin A0).

Todo:

Measure the capacitance at different intervals to observe how it changes over time. Measure temperature dependency and frequency response?