Saturday, October 2, 2010

Bluetooth Power Monitor

All the recent talk of power conservation got me in the mood to adapt my power meter from a couple posts ago to be a little (just a little) more practical. With a little bit of re-working, I was able to recycle (eco-friendly) my code from the Bluetooth thermometer and use it to transmit measurements from the CT (Current Transformer) to a terminal program via the Bluetooth link.

Figure 1.0: Bluetooth Power Meter Hooked up to My Toaster Oven
With a little bit of hacking around in Proton (PICBasic Development Suite) I was able to get the thing working; at the moment it spits out a a reading every second in amps. I didn't want it to give an answer in watts since it isn't measuring the actual AC line voltage (yet), and therefore any power readings would be a sham if it used some arbitrary value like "120VAC" for the line voltage. The next step is to find a small transformer out of a clock radio or something (~6V secondary) and design a small circuit to give us a small DC voltage proportional to the AC line voltage that the PIC can then measure and use in power calculations.


-  I've run out of room in the PIC12F675 - It can only store one float variable. 

- The CT I'm using blows - The scale goes from 0-10A, but when I plug in my coffee maker that pulls 7.37A (900W/122V), the output voltage of the CT is around 4.75V, when in reality it should be about 3.7V

Figure 2.0: Terminal Output @ 9600 Baud over Bluetooth

As you can see it works as-is, if you'd like a copy of the source code give me a shout and it's all yours; just be warned that you'll need a PICBasic compiler to do anything with it. I could also send you a HEX file if you want to use it as-is. As with the thermometer, once I get something working that does more or less what I want it to do I'll draft up some schematics and maybe even a PCB. Stay tuned.

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