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Progress

Posted 2011.01.22 21.16 in Computers/Internet/Technology, Pointless Blather

It’s slow, and I hope I’m not jinxing myself by saying it, but I think there’s some progress.

The ethernet port seems to be working(*). The temperature variances are annoying but I think I’ve found ways to live with it. Last night I added all the buttons and switches. All that remains now is to build the circuit board that will house the power regulator and the interface to the HVAC lines.

I had been worried about how it will all look – especially with the Chronodot RTC/temp sensor being not only external, but standing off about an inch. I was worried also about mounting buttons and switches. Would I do a good job? Would they look ok? Would it look like a 3rd grade science fair reject?

In a moment of zen, I found a peaceful answer to all these concerns. My thermostat is going to look a little bit like mad science. People are going to be wary when they see it. People are going to be afraid to touch it. And that is the way it is meant to be.

The grey wire coming out the bottom is the ethernet cable. The blue board & black cable on the left side is temporary, it is the USB/serial connection that I’m using for debugging, and temporarily providing power to run the thermostat. Down below to the right of the ethernet port, is where I’ll be building the power & HVAC interface circuitry.

* There is one ongoing sporadic problem with the ethernet port. Sometimes after a power loss, it hangs on initialization. I suspect I know what the problem is, and how to remedy it. For now, it just means occasionally having to hit a reset button after power-up.

I’ll include some pics of the guts in my next update post.

So. Many. Wires.

Posted 2010.12.31 18.58 in Computers/Internet/Technology, Hobbies

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. 😉