If you are losing sleep due to any of these burning questions, then perhaps you should build this project. This contraption uses a laser and photo resistor to non-intrusively measure the rotational speed of that ominous disk inside the electric meter.
With this information, we can calculate how many Watts we’re pulling. Then we can feed the data into a monitoring program such as MRTG, and get a nice plot of energy usage over time.
There are basically three parts to this:
The photo interrupter assembly, consisting of a cheap laser pointer and a photo resistor, mounted above and below the power meter. These detect the movement of the disc by shining light through the hole(s) in it.
Some analog circuitry, which filters and amplifies the signal from the photo resistor.
A program which measures the pulses and calculates some interesting numbers
You’ll need one pair of wires to get from your computer to your power meter. I had an extra pair of telephone wiring available, so I didn’t have to run any wires. I made every effort to keep the electronics simple and minimize the amount of wiring, because I didn’t want to spend more than a weekend getting this to work.
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