fix: switch ADC reference from FVR to VDD #20

Merged

daru merged 1 commit from fix/adc_reference_vdd into main

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

time commented

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

Contributor

Fixes #3

Switched ADC reference from FVR (2.048V) to VDD (battery). FVR is now read as an ADC channel to determine VDD, freeing RA1 for other use.

Changes:

Firmware: ADCON1 ADPREF=01 (VDD ref), added ADC_FVR channel, read FVR instead of battery on RA1
Decoder: temperature formula uses FVR reading: Vt = 2.048 * (1023 - temp_raw) / (4 * fvr_raw), Temp = (0.659 - Vt) / 0.00132 - 40
README: updated to reflect ADC reference decision

Fixes #3 Switched ADC reference from FVR (2.048V) to VDD (battery). FVR is now read as an ADC channel to determine VDD, freeing RA1 for other use. Changes: - Firmware: ADCON1 ADPREF=01 (VDD ref), added ADC_FVR channel, read FVR instead of battery on RA1 - Decoder: temperature formula uses FVR reading: `Vt = 2.048 * (1023 - temp_raw) / (4 * fvr_raw)`, `Temp = (0.659 - Vt) / 0.00132 - 40` - README: updated to reflect ADC reference decision

time added 1 commit

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

fix: switch ADC reference from FVR to VDD, measure FVR to determine battery voltage e14ec4acf3

Previously the ADC used FVR (2.048V) as reference and measured battery via
an external divider on RA1. The temperature formula in the decoder used this
battery reading, which was fragile and incorrect.

Now the ADC uses VDD as reference, freeing RA1 for other use. The FVR is read
as an ADC channel to determine VDD: VDD = 2.048 * 1023 / fvr_raw. The
temperature formula becomes VDD-independent when FVR is used:

  Vt  = 2.048 * (1023 - temp_raw) / (4 * fvr_raw)
  Temp = (0.659 - Vt) / 0.00132 - 40

This also fixes the temperature calculation per AN1333 and frees an analog input.

time referenced this pull request

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

temperature formula uses battery voltage instead of FVR reference #3

daru merged commit 99d6c71d77 into main

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

daru referenced this pull request from a commit

2026-07-27 02:12:22 +00:00

Merge pull request 'fix: switch ADC reference from FVR to VDD' (#20) from fix/adc_reference_vdd into main

time referenced this pull request

2026-07-27 02:18:43 +00:00

README says ADC reference undecided, firmware uses FVR #7

~~time referenced this pull request 2026-07-27 02:18:51 +00:00~~