boards/feather-m0: Correct ADC Settings #21508
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The current ADC settings set the reference to the internal 1V reference with a x1 gain. This means that the maximum voltage that can be measured with any analog input is 1V, which is usually not sufficient for most applications. Therefore the default value is changed to use the external VDDA input, which is 3.3V (internally divided by 2) and the gain to x1/2. This allows to measure voltages up to VDDA on any analog input.
Teufelchen1
approved these changes
May 24, 2025
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Thanks :) |
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Contribution description
The current ADC settings set the reference to the internal 1V reference with a x1 gain. This means that the maximum voltage that can be measured with any analog input is 1V, which is usually not sufficient for most applications.
Therefore the default value is changed to use the external VDDA input, which is 3.3V (internally divided by 2) and the gain to x1/2. This allows to measure voltages up to VDDA on any analog input.
Testing procedure
You can run the
tests/periph/adcexample with an external voltage source connected. You should see that withmaster, the ADC values max out at about 1V (or 2V for the battery input).I connected a 0.8V voltage to the BAT input, which has a 1/2 resistor divider.
master: The values should be 0.8/1.0 * 0.5 * {256, 1024, 4096, 65536} = {102, 410, 1638, 26214} on ADC_LINE(6)):This PR: The values should be: 0.8/3.3 * 0.5 * {256, 1024, 4096, 65536} = {31, 124, 496, 7944} on ADC_LINE(6)):
Issues/PRs references
Found in #21022.
The ADC configuration was set when the Feather-M0 was introduced in #7510 and never changed since.