I intended to use the ATtiny84 remote RFM12B sensor to measure my solar hot water tank, but once the temperature reached 57.05, it wouldn’t measure any higher. I assume this is due to the 1.1V reference limit used to measure, checking the TMP36 datasheet also suggests that around that voltage the temperature is roughly what I see. So this was no good for me, the solar water tank can reach 90 and even more degrees Celsius. So I replaced the analog TMP36 with a digital DS18B20 and modified the code accordingly. I had to place and additional 4K7 resistor between the Vcc and RQ legs of the DS18B20 as shown below:
The software part was a bit tricky, to get the code to compile follow carefully the discussion here. I needed two temperature sensors with the board, so that’s also an improvement over the old design: it can now take multiple temperature sensors on the onewire bus.
Here is my updated code on github.
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