Tracking power usage with a raspi

With tiny, Internet-connected computers everywhere these days, home automation is finally hitting it big. [Jelora] was looking for a few more home automation projects and realized his electric meter had a pair of ‘digital information outputs’. With a Raspberry Pi and a few bits of wire, he figured out how to read this digital output and put a log of his electricity consumption up on the web.
The digital output on [Jelora]’s meter is a bit odd; it’s 1200 bps, 7 bits per character, parity, with one stop bit. It’s also a 50 kHz AC signal for a binary ‘0’ and nothing for a binary ‘1’. To read this signal, [Jelora] is using a diode to throw out half the signal, a 6N138 optoisolator so the Pi isn’t connected directly to the meter, and a small cap to smooth out the signal. Simple, and it works.
This cleaned up signal is then connected to serial to USB chip and a PHP script scrapes the data every minute. The data received from the meter is stored in a data base along with a few other bits of information: if the meter is being charged peak or off-peak rates, and the price per kWh. All this is saved on an IDE hard drive (more reliable than the SD card, surprisingly), and a ‘electricity cost per day’ is plotted on a nifty graph and served up by the Raspberry Pi.
http://hackaday.com/2015/01/18/track...-with-a-raspi/