ESP32 Forum

Using the Arduino IDE, the ESP32-S2 ADC1 channels (GPIO 1 through 10) work fine and gives back the expected reading.

[Codebox]
// Read ADC (30V DC FSV - 0 to 8191 - 13bit)
uint32_t PCB_Voltage;
PCB_Voltage = ((analogRead(9) * 30 ) / 8191);
Serial.println(PCB_Voltage);
[/Codebox]

However, if I use any ADC2 channels (GPIO 11 through 20) ), I get an error:

[Codebox]
// Read ADC (30V DC FSV - 0 to 8191 - 13bit)
uint32_t PCB_Voltage;
PCB_Voltage = ((analogRead(17) * 30 ) / 8191);
Serial.println(PCB_Voltage);
[/Codebox]

E (4127) ADC: /Users/ficeto/Desktop/ESP32/ESP32S2/esp-idf-public/components/driver/adc_common.c:476 (adc2_get_raw):WIDTH ERR: ESP32S2 support 13 bit width

PS. The below basic code does the same, only on ADC2, so excluding any value manipulation

[Codebox]
analogReadResolution(13);
Serial.println(analogRead(17));
[/Codebox]

Please does this error jump out at anyone?

Thanks in advance!

Dave

Looks like ADC1 can support RTC mode for 13 bit readings, but the ADC2 cannot. It is not clear whether this is a permanent restriction or an artifact of beta code, but it is what it is at the moment. You can ask at https://github.com/espressif/esp-idf/issues for more detail.
https://github.com/espressif/esp-idf/bl ... mon.c#L482

Many thanks for the thoughts. Seems to parallel mine but was not sure.

Will post a comment as per.

Take care
Dave

I found that using analogRead(1) on Arduino gives unexpected results out of the box. Connecting GPIO1 (ADC1_CH0) to VCC/2 (1.65V) results in a value of 8191 (instead of around 2047 as expected for a 12 bit result at half-scale).
After reading the documentation, I understand that after reset ADC1 is configured for 13 bits, with 0dB attenuation, which results in a full-scale range of 0 to Vref (which is nominal 1.1V, but can vary from chip to chip by as much as 20%), mapped to 0-8191.
See also: https://docs.espressif.com/projects/esp ... s/adc.html