After creating wireless compost monitor I was wondering what else could be done with the same card. I then saw a commercial about a gadget which displays house electricity usage in real time. The idea of the device is to help saving of energy. The gadget had a small box that apparently monitors how frequently the led on KWH-meter blinks (on our meter, it blinks once per 1 Wh) and sends that information to indoor visual display unit, which converts it into kilowatts.
Schematic for KWH meter monitor
The commercial gadget looks really nice, but of course I had to make my own. The MOD-CCRF card is just perfect for system like this. I just added a phototransistor with pull-up resistor to keep on eye on the blinking led. After checking that my “eye” was really able to see the blinking led I added some code to existing wireless monitor application to calculate house electrical power from blink count. The monitor unit sends the data then to same wireless access point as the compost unit for saving results in database.
Monitoring unit attached to KWH meter. Box contains the MOD-CCRF card with phototransitor circuit and two AA sized batteries.
Our KWH meter is in a small ‘closet’ which has a transparent plastic door. By attaching velcro strips to the door and back of the monitor box I was able to position the unit exactly over the blinking led.
I also created a simple chart to monitor results (last trend at bottom of page).