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.