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Tinkerers’ Rules

Posted 2011.05.15 10.34 in Computers/Internet/Technology

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Quoth the Maker: If you can’t open it, you don’t own it.

Updated Already

Posted 2011.03.20 22.10 in Computers/Internet/Technology

I couldn’t leave it alone, of course. Had to take it apart again today and make an update.

That thing with the WizNet module hanging sometimes, I had applied a very makeshift fix to yesterday. See, the WizNet doesn’t have its own power-on reset, but it needs it. They suggest you use a digital pin from your uC but I was out of pins. So I used a 10uF capacitor, which was enough to ground the reset line on power-up or manual reboot.

The problem was, I had my WizNet reset tied to my Arduino / ATMega reset, and the capacitor meant I couldn’t update the programming. At least, not without temporarily removing that capacitor.

So it turned out, I did have a spare pin. I had been holding A3 in reserve. Just incase the temperature readings from the Chronodot remained inaccurate due to the heat from the WizNet, I was prepared to add a TMP-36 analog temperature sensor, and dangle that a few inches below the enclosure. Luckily, with the thermostat mounted vertically on the wall, and the Chronodot a good 1″ out with open air around it, the temperature readings are accurate.

So I pulled it open, removed the capacitor, and unhooked the WizNet reset line from the Arduino / ATMega reset line, and tied it instead to A3. A few quick changes to the software, and presto, no more hang-on-powerup and it can be reprogrammed without any soldering. Yay!

Also, I decided to go ahead and show off the guts. Why not? Just be warned, if you’re easily upset by ugly wiring hacks and poorly-planned soldering and random wires and tapes and dead-bug construction… well just don’t look.

And finally, here’s a link to the updated software. The zip file also contains a text file that outlines the pinout & functions for the ATMega chip, the WizNet module, and the function of the HVAC lines — or at least, how they function in my house.