I’m new to electric imp but it looks really cool! I want to get one to measure temperature of an air-conditioned room, and check the power usage of the a/c unit, and create reports for both wirelessly.
It looks like if I got the impExplorer kit that should cover the temperature sensing, and then I was thinking of the SCT-013-020 to measure power usage. It looks like the cable on that goes to a 3.5mm connector - what would I need to connect that to my impExplorer?
You’d need to plug that into one of the non-i2c grove connectors, with a “burden” resistor across the coil and the coil between the input pin and ground; this will then turn the current flow sensed by the clip-on transformer into an analog voltage that you’d sample with the sampler (as it will vary at your mains frequency) and then integrate.
Not super straightforward, but not impossible either. Have a look at this old post on the forums for some code (use the version that uses the sampler):
The SCT-013-100 doesn’t have a burden resistor, at least the one that I have doesn’t but they probably come in different variations.
It does have a protective zener diode though. I hate to think what the voltage would be on the 3.5mm plug without a burden resistor or diode.
The voltage across the burden resistor will follow the AC cycles, so for my hobby project I sampled it quickly into an array for a fixed time then did some maths on the results. Undoubtedly there’s much better ways to measure the varying voltage but it gave pretty good results above 100watts (0.24amps).