Using a sound card as an electricty meter

Just some quick notes on using a 20bit 96kHz sound card on Linux (Ubuntu Server) to sample measurements from a current transformer and AC-AC adapter.

I followed this guide to get audio working on Ubuntu Server. I then tinkered with Audacity (using X over SSH). (My ultimate plan is to either use arecord to record the signal or write a Python or C++ program to do the sampling and processing).

I used the standard Open Energy Monitor current transformer with a 22 ohm burden resistor (which gives about a 0.89V peak-to-peak output when presented with a 30 amps RMS primary current: 0.89V peak-to-peak is, according to WikiPedia, the standard for line inputs and 30amps RMS is, I believe, the most my house every pulls)

For the voltage reading, I'm using the standard Open Energy Monitor AC-to-AC converter. This feeds into an 80mA fuse, then into a simple resistor divider (10k and 220ohms). This gives about 0.7v across the 220ohm resistor which is fed into the sound card's line input. I use two 1N5282 diodes (1.3v forward voltage bias) in parallel across in the 220ohm resistor to guarantee that the peak to peak voltage never goes above 1.3v.

More details on the OEM forum.

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Comments

You're rather hopeful that -10dBV is "standard" ;) Ok, I'll grant you it's a vague standard. That might make calibration slightly more interesting!

ah, yes, good point. I'm planning to calibrate each sound card separately.

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