ESP32-S2 analogRead function not returning correct value

[brentru]

Hardware:

Board: Adafruit FunHouse ESP32-S2
Core Installation version: 2.0.0
IDE name: Arduino IDE
Flash Frequency: 80Mhz
PSRAM enabled: Yes
Upload Speed: 115200
Computer OS: macOS and Ubuntu

Description:

Calls to Arduino's analogRead (https://www.arduino.cc/reference/en/language/functions/analog-io/analogread/) function are not working on BSP v2.0.0. It seems to always return a value of 0, instead of the correct value from the ADC. This functionality was working prior to 2.0.0.

Sketch: (leave the backquotes for code formatting)

void setup() {
  Serial.begin(9600);
}

void loop() {
  Serial.println(analogRead(A3));
  delay(100);
}

[felmue]

Hello @brentru

do you know which GPIO corresponds to A3? I am only seeing A0 to A2 looking at the FunHouse pinout.

Some analog inputs share the same ADC module with WiFi and fail to work when WiFi is turned on at the same time. Have a look here.

That said, have you tried to turn off WiFi? Have you tried with a different analog input?

Thanks
Felix

[brentru]

@felmue - looking at the board variant (https://github.com/espressif/arduino-esp32/blob/master/variants/adafruit_funhouse_esp32s2/pins_arduino.h#L53), it'd be GPIO18.

Some analog inputs share the same ADC module with WiFi and fail to work when WiFi is turned on at the same time. Have a look here.

We've had success reading the analog input using the same code, prior to the v2.0.0 BSP update.

Have you tried with a different analog input?

We've also tried reading the value of a pot. with analog pin A0.

That said, have you tried to turn off WiFi?

I'm not sure how to turn off the ESP32's WiFi via the Arduino IDE.. The sketch attached with the issue doesn't perform a network setup.

[felmue]

Hello @brentru

understood, afaik some WiFi stuff has been changed in v2.0.0 and now it can interfere with reading analog inputs.

Well, A0 and A3 are both using the same ADC module (ADC2) as WiFi so I'd expect it to fail as well. Could you try A1 or A2?

If in the past you've ran a sketch using WiFi there is a chance it is still running (in the background) even though your current sketch isn't using WiFi. You can try to stop WiFi using this: WiFi.mode(WIFI_OFF);

Thanks
Felix

[atanisoft]

@felmue WiFi and ADC is only a problem on the ESP32 and not ESP32-S2/ESP32-C3 chips.

[felmue]

@atanisoft

thank you for sharing - I wasn't aware of that.

Any idea what the issue @brentru is facing could be?

@brentru : sorry, but I am out of ideas. Hopefully somebody else can help you.

Good luck!

Thanks
Felix

[atanisoft]

According to Adafruit FunHouse schematic A3 (GPIO18) is connected to a light sensor output pin with a 10k pull-down resistor.

Based on this, it would make sense that you are receiving a zero value for analogRead().

[felmue]

Hello @atanisoft

but the light sensor should be able to pull it above 0 when it catches some light, wouldn't it?

And according to @brentru it worked with an earlier version of Arduino, e.g. before v2.0.0.

Thanks
Felix

[atanisoft]

Depends on the sensor, it also couldn't have worked in v1.0.x as the S2 wasn't supported in that version. Since I don't have the board I can't do any testing.

[ladyada]

@felmue @atanisoft do you have other ESP32-S2 boards that you can test analog input with?

[atanisoft]

@ladyada I haven't tested ADC on the S2 in a while but last I checked it was working with the Saola and WROVER modules that I have. There have also been a few issues filed about ADC attenuation defaults not working correctly and the ADC returning 4095 (max value). But in this case it is returning zero which indicates that either the wrong pin is being read or it is remaining at GND.

[ladyada]

@atanisoft ok - did you try analog input with 2.0.0? if not, is there someone who can try to replicate this bug so it can be assigned?

[chegewara]

Yes, i can confirm there is at least 1 bug. By default it is setup 12 bit width, but:

For ESP32s2, only Two Point values calibration and only ADC_WIDTH_BIT_13 is supported. The parameter default_vref is unused.

and i am getting this error:

E (58030) ADC: adc2_get_raw(578): WIDTH ERR: see `adc_bits_width_t` for supported bit width
[ 58490][E][esp32-hal-adc.c:174] __analogRead(): GPIO18: ESP_ERR_INVALID_ARG

EDIT
here is this bug described and how to solve it, now only PR is required:
#5658

[felmue]

Hello guys

I ran some tests with an ESP32-S2-Kaluga-1 board and can confirm that the issue seems to be related to the analog resolution. The only resolution working for GPIOs using ADC2 seems to be 13. Unfortunately analogReadResolution(13) doesn't seem to help. Below code fails with this error:
E (100335) ADC: adc2_get_raw(578): WIDTH ERR: see 'adc_bits_width_t' for supported bit width

void setup()
{
  Serial.begin(115200);
  analogReadResolution(13);
}

void loop()
{
  Serial.println(analogRead(18));
  delay(2000);
}

However I was able to read the analog value from GPIO18 with the following code. Inspired by the ESP-IDF adc2 example.

#include <driver/adc.h>

int read_raw;
esp_err_t r;

void setup()
{
  Serial.begin(115200);
}

void loop()
{
  // ADC2_CHANNEL_7 is GPIO18
  r = adc2_get_raw(ADC2_CHANNEL_7, ADC_WIDTH_BIT_13, &read_raw);
  if ( r == ESP_OK ) {
      printf("%d\n", read_raw);
  } else if ( r == ESP_ERR_INVALID_STATE ) {
      printf("%s: ADC2 not initialized yet.\n", esp_err_to_name(r));
  } else if ( r == ESP_ERR_TIMEOUT ) {
      //This can not happen in this example. But if WiFi is in use, such error code could be returned.
      printf("%s: ADC2 is in use by Wi-Fi.\n", esp_err_to_name(r));
  } else {
      printf("%s\n", esp_err_to_name(r));
  }
  delay(2000);
}

Thanks
Felix