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I am looking to use the Raspberry Pi 2 to measure the power consumed by household appliances. I know that the Pi does not have an inbuilt ADC. I found that the MCP3008 can be interfaced with the Pi as an external ADC. Can I use this to measure voltage and current, and are there any tutorials that I can follow?

angussidney
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Rohit Seshadri
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    This could be an interesting project and you might learn a lot doing it. But if you just want to get the answer, consider purchasing a "Kill A Watt" device. It will be much cheaper and easier. http://www.p3international.com/products/p4400.html –  May 21 '15 at 18:20
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    Have a look at ubiquity networks mpower and mport products –  May 21 '15 at 19:11

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Here goes, quick tutorial: -

  • Power = volts x amps
  • This applies to AC as well as DC
  • Irrespective of power factor, power = volts x amps
  • You'll need to sample the voltage and current signals at about 1kHz or harmonics in the current waveforms will alias the ADC and give false readings of power
  • Once you have a means of digitizing v and i multiply the instantaneous values and average the results through a digital low pass filter.
  • This gives you average power
  • Energy companies bill you (usually) as kW hours so integrate the average power over time to create kWh

You'll either use a small voltage transformer to give a voltage reference you can digitize or maybe a resistive potential divider BUT beware, the r-divider means your ADC and Micro are at potentially life-snuffing voltages.

For current use a hall effect device or a CT.

  • I was planing to step down the supply voltage by using a voltage divider and give it to the MCP3008 and interface it to the raspberrypi for the calculations. Can I do it that way? –  May 22 '15 at 18:37
  • Read my penultimate paragraph. –  May 22 '15 at 20:07