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enl

Electronic Thermometer with analog meter

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I spent some time last year setting up an analog meter driver/thermometer for a client, and at the time, I went through my stock of junk^H^H^H^Hreclaimed parts and found a phase angle meter with degree graduations on it. I said to myself "since I alredy wrote the code and did the dev work on someone elses dime, I should throw one together for myself". A year and a half later, the holidays hit and I was looking for something to do instead of paperwork for work.

 

So, I layed out a single sided board (the original was on a launchpad), cut it on the mill, and populated it.

 

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There was a couple days in the middle between cutting and populating (the holiday, you know), so I had a surprise. The astute amongst you might notice something missing on this layout, given that this is a low power project that will require stable voltage for the analog meter. Yup. No regulator pads.Finished soldering up the board and sitting there in the tray is the regulator. Whoops. I didn't feel like going whole hog (including changing a setup on the mill) for a board just to hold the regulator and a couple caps, so I pulled out a sharpie, a scribe, and an ancient bottle of ferric chloride. 20 minutes later, I had an etched board that would do the job. Ugly, but functional. The layout for the main board will be revised in case I reuse it.

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It doesn't look so bad populated.

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The wire is for USB power.

dubnet likes this

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The board sockets on to the power header

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The 5-pin with the cable going to the right is for a button and double pole, center off momentary switch for adjusting the scale in operation. The software does linear interpolation from 0 to 100 degrees F, and allows for key points every 10 degrees. The three yellow wires go to the remote sensor (DS18B20). The mounting is leftover oak from redoing a floor. Glued up, planed, bored for the meter and the electronics, and finished to hang on the wall. The circuit board is mounted by putting epoxy in the pocket and dropping it in.

 

Power board on. The tie point for the power line isn't on yet.

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The face of the finished display:

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The finish is shellac. I slopped on a heavy coat, light sanded, and then wiped another couple on. Then paste wax. Not perfect, but I banged it out quickly.

 

The meter:

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Operating. The temp in my shop has climbed to 66F with a lot of help from the electric radiator.

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zeke, Rickta59, chicken and 1 other like this

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