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wagiminator / ATmega-Soldering-Station

T12 Quick Heating Soldering Station
https://oshwlab.com/wagiminator/z-solderingstation-smd-v2
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T12 Thermocouple uV per degree Celsius question #13

Closed SmallpTsai closed 3 years ago

SmallpTsai commented 3 years ago

Hello, In the readme, it said the delta is roughly 40 uV per degree Celsius but that is no match to the default calibration temp in firmware. Please help to correct me If my calculation is wrong.

  1. Vcc = 5V
  2. the gain of opamp is set to 201 (1 + 200K/1K)
  3. default calibration:
    • 200/216 -> (200 5 1000000) / (1024 201 216) = 22.49
    • 280/308 -> (280 5 1000000) / (1024 201 308) = 22.08
    • 360/390 -> (360 5 1000000) / (1024 201 390) = 22.42

so the actual delta should be ~22

Is there any calculation error above? Please help me to understand the logic. Thanks !!

wagiminator commented 3 years ago

You're right, there's a mistake in the description. I will correct that. The 40uV was based on the assumption that there is a k-type thermocouple in the T12 soldering tip. But that is obviously not the case. The corresponding values in the software are derived empirically and have worked so far.

SmallpTsai commented 3 years ago

thanks for your answer!