temperature formula uses battery voltage instead of FVR reference

daru commented

2026-07-26 17:01:47 +00:00

Owner

cryogencc_pickle_01.c computes temp_c using batt_v in the formula. AN1333 specifies VTEMP = temp_raw * 2.048 / 1024 using the FVR reference, not battery voltage. Current formula will give wrong readings.

Fix: use FVR 2.048V as reference in the temperature calculation.

cryogencc_pickle_01.c computes temp_c using batt_v in the formula. AN1333 specifies VTEMP = temp_raw * 2.048 / 1024 using the FVR reference, not battery voltage. Current formula will give wrong readings. Fix: use FVR 2.048V as reference in the temperature calculation.

daru commented

2026-07-26 19:44:20 +00:00

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Owner

I'm not sure, actually, if this is correct. Need to check if VTEMP scales with battery voltage.

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2026-07-27 01:38:51 +00:00

daru commented

2026-07-27 01:39:00 +00:00

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Owner

It would be best to figure out how to use the battery as the ADC reference voltage for everything, and to simply measure the FVR with the ADC, which will directly give us battery voltage and will extend the measurement range of the ADC by about a volt.

Needs additional work.

It would be best to figure out how to use the battery as the ADC reference voltage for everything, and to simply measure the FVR with the ADC, which will directly give us battery voltage and will extend the measurement range of the ADC by about a volt. Needs additional work.

time referenced this issue from a pull request that will close it,

2026-07-27 02:09:02 +00:00

fix: switch ADC reference from FVR to VDD #20

time commented

2026-07-27 02:09:02 +00:00

Contributor

Fixed in PR #20: switched ADC reference to VDD, FVR read as ADC channel to determine battery voltage. Temperature formula now VDD-independent: Vt = 2.048 * (1023 - temp_raw) / (4 * fvr_raw), Temp = (0.659 - Vt) / 0.00132 - 40.

Fixed in PR #20: switched ADC reference to VDD, FVR read as ADC channel to determine battery voltage. Temperature formula now VDD-independent: `Vt = 2.048 * (1023 - temp_raw) / (4 * fvr_raw)`, `Temp = (0.659 - Vt) / 0.00132 - 40`.

daru closed this issue

2026-07-27 02:12:21 +00:00

daru commented

2026-07-27 02:12:32 +00:00

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Builds, good change

Builds, good change

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temperature formula uses battery voltage instead of FVR reference #3