Electricity Consumption Monitor… A Step Forward

With some very helpful basic electronics advice from NJC (of NJC’s MSP430 LaunchPad Blog), and others on the Four-Three-Oh! forums, I rebuilt my IR sensor with a lower value pull-up resistor.  I used the same IR sensor (salvaged from an old mouse), but since it actually had two phototransistors in the part, I wired them in parallel and gave it another trial.  On that partly cloudy day, it worked!  I have yet to test it in full sunlight, but I have hope.

The lower pull-up resistor value helped (I got better range when I tested it on a breadboard with a single side of the sensor), but I think wiring both phototransistors in parallel cut back on the resistance through the sensor as well.  For this reason, I would suggest using a mouse-style dual IR sensor wired in parallel if you choose to try this project.

I went to a tire store and got an old trash inner tube for free. I cut a strip of rubber, cleaned it, and super-glued it into a loop to fit around the meter. I punched a hole with a nail and fed the wire (from the same old mouse where I salvaged the phototransistor) through the hole; it fits water-tight. I decided I might as well use both of the IR phototransistors in the unit, so I soldered three wires to it and super-glued it in place at the right distance from the edge. It fits pretty well!:

I bought a PVC conduit corner piece similar to the larger ones connecting to my meter and feeding into my house. I cut the back connection off, and sealed the back hole with scrap rubber and super-glue. I also used some rubber over the bottom opening to feed the wires through (and keep spiders out). I put a small strip of 1/4″ plywood inside, super-glued a terminal strip to it, and ran screws through the terminal strip, plywood, and rubber and out the back hole to mount to the house.

I ran a piece of CAT-5 cable through an existing hole in the side of the house and into my basement, where the microcontroller and computer will be. The CAT-5 and the terminal strip give me eight conductors in case (when) I run more sensors outside.  I did have a setback that the screws on the terminal strip are ‘cupped’ underneath, so they kept cutting the thin solid CAT-5 wires.  I solved this with a pair of washers per screw.  The only sensor connected so far is the IR phototransistor for the meter (top two terminals on right).  I forgot to get a shot with it all closed up, but it fits visually with the other utility conduit and boxes around it.

I have tested the connection inside, and I am able to detect the pulses on my DMM (drops to ~5 ohms) and with the LaunchPad (triggers an interrupt reliably).  Next up: Firmware and software. More when I get it running!