So. Many. Wires.

Posted 2010.12.31 18.58 in Computers/Internet/Technology, Hobbies by Stephanie

The DIY Thermostat project hasn’t gotten as far along as I had hoped. Or, it has moved forward in leaps and bounds. Depends on how you measure progress, I guess.

I haven’t started building the finished project, it is still on the breadboard. However, I’ve expanded the breadboard to include all the working parts, i.e. the finished button layout, and the relays that will control the furnace and air conditioner.

I’ve also changed plans, in terms of the communications.

I was originally working with Bluetooth, and indeed had a working prototype with a bluetooth module. I wasn’t too happy however with the BT functionality. It was not that reliable, I found — as in, being able to ‘guarantee’ that I could connect to it every time, automatically, any time I tried. There’s that messy handshake business, with PIN numbers and stuff, and that seemed to be a hang-up.

Also, ultimately it would have been paired with my server which is Linux, and there seemed to be more issues there, getting the paired connection and the PIN numbers and blah blah blah. It was looking aggravating.

My plan-b was to use a different wireless scheme, the XBee modules. These looked attractive in that at the computer-end it would just be a usb-serial port, and would be always connected. However, there were some cost issues (It would have run about $100 for the modules etc. to achieve what I wanted) and again, no guarantee of 100% reliable connectivity.

So on to plan c. Good old safe, secure, and reliable ethernet. Getting from wireless to wired didn’t happen in one step. I was also dealing with the power requirements my Thermostat had. I didn’t want to have to constantly feed it batteries, and my design looked like I was going to need 3 or 4 AA batteries to fully power it. So I was already starting to accept that I would probably have to run some extra wires into the thing, to provide 5vdc.

With that on my mind, and looking at the communications options, I realized that I could solve both the power and comms issues with a single Cat5 line. Power over ethernet. I can use mode B, grab one of the unused pairs in the Cat5 cable, and pump the power in there, from my switch. Then at the thermostat, I just tap the power pair and run it through a regulator and hey presto, 100BaseT link, and power too!

Here’s the new version of the prototype, breadboarded with the relays, switches, and — yeah, that’s an ethernet port up there on top.

So the next step (again) is to start building all this into the finished project box; moving it off the breadboard and into the final package. Also, there’s some more coding to be done, to get the ethernet comms working right.

I can’t build a complete web server into it — not enough space left in flash or ram. I’ll create my own little thermostat protocol and then create a web interface for it on my home server. And the iPhone app that I will be creating. 😉

End of the Year

Posted 2010.12.31 18.19 in Pointless Blather by Stephanie

So 2010 is drawing to a close in a few hours. It went by quickly, except when it was going slow. There were ups and downs. Mostly downs. All in all, I’d rate it about a 4. Solid “Meh.”

Nearly adequate.