With the advent of summer weather in June 2008, I had yet another concern that the upstairs air conditioning was not performing correctly. The best way to monitor the performance is to monitor inlet and outlet temperatures along with attic ambient. Hopefully this will highlight any problems we may be having with air cooling or air heating.

The device chosen to do this is AVR based because I had the hardware and tools. The sensor is the ubiquitious One Wire DS1820 from Maxim which I have lots of experience with. A major plus to the DS1820 is the fact the probes are pre-calibrated at the factory. I will be enclosing the chip inside a copper probe using a technique developed for the Kahlo project.

Unique for me is the addition of more than a single probe to a wire. The former QYX terminal I hacked for this purpose only had one convenient port pin. I tried to rewire an old network/ethernet switch to serve as a passive one wire hub. This didn't work because two of the pins are connected together internally. When I took the multiple RJ45 connector off with a blow torch I saw the traces for the internal connections. I ended up gluing brand new individual RJ45 conns to a baseboard and hand wiring the pins as my hub prototype. I will have to make a circuit board and have all the probes plug into the hub with one probe coming from it to the AVR subassembly. This AVR assembly has a Digi Xbee module for wireless connectivity.