You can view all of the construction pictures here.
The first step was running the plenum rated cable down the air returns. This may not meet code in your area. Most of my return vents went straight down to the basement, so all I had to do was get the cable down between floors and then find a way to fish it out. Getting the cable into the basement was actually a lot easier then I had anticipated. I just attached a plumb bob to the end of the cable and dropped it down. I had my wife wiggle the cable a few times while I went to the basement and just listened for where the racket seemed to be coming from. The return vents in our home use the joists and decking, so getting to the cable was a simple matter of removing a tin panel and grabbing the wire.
The next step was to find a connector that would hold the sensor securely but would allow me to take it out easily if I needed. I searched high and low and eventually found that the 3 pin connectors on old computer case fans were about the best thing going. They have a solid build, can be found easily and they allow the leads of the DS18S20P devices to sink in nice and deep.
The two outside legs of the 18S20 need to be tied to ground. I figured that the easiest way to do that was to simply pin the ground legs together at the connector. This also meant that I was able to run the entire 1-wire bus to the various rooms of the house using only a single pair of the CAT-5e, leaving 6 wires for other stuff!
After soldering the ends to the CAT-5e (OK, I soldered some and crimped the holy hell out of others) I was able to mount the connector and sensor into the return vent. I decided to angle the sensor towards the center of the vent hoping to catch a more realistic view of what the room temperature is like. I decided on the return vent for two reasons. The first being that it is generally the farthest away from the register, which means it will be impacted the least by the cycling on and off of the HVAC. And the second being that when the HVAC is on, the air being sucked into the return will again be the most accurate depiction of the room simply because it has to come from all four corners.
The last temperature sensor is actually outside the house. The problem is that the 18S20 is anything but weather tight. I got around this by taking some 1/4 OD copper refrigerator cooling line and crimping one end. I then filled that end up with silicon caulk. Next I used an entire 1.5g tube of thermal paste and filled up the remainder of the pipe. After soldering leads onto an 18S20 and covering those in shrink wrap, I inserted the sensor into the copper and sealed the end up with more silicon. I then used some heat shrink and encased all three leads together, then some even larger heat shrink and wrapped up the copper and the leads. I got the idea to use the copper tube from here, but it seems to be a pretty common practice.
This sensor is mounted on the outside of the house, out of the way of direct sunlight as much as possible. I may end up having to place it inside of a dome to block out even more sunlight, but we’ll see.
Next: Building the Controller
