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.


test said...

Have you tried or seen

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.

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.