The idea is very similar to the chicken coop dimmer
. However, I want to add a readout and temperature adjustments.
The first step was disabling the heating pad's auto-off feature, which interrupts power to the heating elements if the pad has been on for more than 60 minutes. The Kaz HP215 SoftHeat
heating pad, found at Wal-Mart, is the victim. After I got the case open, I examined the circuit within. I noticed a transistor near the output to the pad, and looked up the part number. It is a z0103 Triac, used to switch high-voltage power. Following the trace, I noticed it was connected to the mystery microcontroller's (try to find a datasheet for a 13-000022
) pin 2. I hit it with the iron and pried the pin up. The device now thinks it is going to sleep (LED flashes) but it can't trip the triac, so my pad stays nice and toasty.
Step two is to get a display working with count up/down on the arduino. I used this great blog post
to get me started. Only thing is I found out: my display's upper left led on the first digit is out, and I needed to reverse the binary in numbers to get it to work (ie 0b1000000 became 0b0111111, etc.).
Step three is to get a real reading on my thermistor
finally. I made a spreadsheet to help me with the math. On the way to that spreadsheet, I made a csv for everyone. Yay! See the attachments section down there VVVV.