Friday, July 30, 2010

What most energy monitors don't tell you!



I received a Efergy Elite energy monitor (sold in Maplin and other retailers) as a Christmas gift few years go. The Elite provides current use, daily and weekly average and all that green CO₂ nonsense. While useful for tracking down unnecessary drains it doesn't give you a true picture of electricity use throughout the day.

The Efergy Elite comprises a wireless sensor and a receiver/display unit. The sensor is a clamp ammeter which clips to the output from your ESB electricity meter. It transmits real time power use [*] to the receiver every 6 seconds. The receiver unit displays the current consumption and computes daily and weekly averages – not a huge amount of extra info that your electricity bill won't tell you.

Despite getting all this juicy data every 6 seconds the Elite won't share it with you. There is no computer port.  So I hacked it.

I soldered a wire on the baseband signal from the radio receiver, into a cheap little PIC MCU for some decoding and at the other end a stream of numbers every 6 seconds. Bung that into a graphing package and you get a chart like that above.



[*] Actually it can only sense current. So you assume that the supply is at a constant 230V rms and you can calculate the power (power = V*I). It's not accurate enough for billing, but certainly good enough for consumer energy monitoring.

4 comments:

test said...

Have you tried or seen http://www.currentcost.com/product-cc128.html

Current Cost energy monitor just like the product your using but has serial port and spits out readings every 6 seconds, and can output historical data aswell over the serial port.

http://infosonic.wordpress.com/2009/03/14/currentcost-electricty-meter/

I have been playing around with the device a bit and created an adobe flex front end application which replicates the display and does some nice graphing.

jdesbonnet said...

Thanks for the tip. It does seem to be a 'friendlier' device. Will see if I can get one and I'll get back to you then. BTW: been looking at gas meters and water meters also: all look very interfacable!

The Cageybee said...

"If you want to see this decoder implemented for other MCUs leave a comment at the end of the blog post and I'll see what I can do."

Yes please. Any chance you could port the decoding voodoo to Arduino? Would be very appreciative if you could.

BTW It seems I have a different revision to yours. The radio section is exactly the same but the rest is totally different. There's a couple of extra unsoldered headers too. One marked 'TR1' the other marked 'HR1', both have 2 solder points. There's also places for 2 chips which are unpopulated on the board and a load of unpopulated passives.

Could upload a picture if you're interested.

jdesbonnet said...

Yes, please do send me an image. My email address is jdesbonnet at gmail dot com. I'll see what I can do about getting you a Arduino sketch for the decoding.