Description
Board
ESP32-S2
Device Description
Tested with Unexpected Maker FeatherS2 & senseBox MCU-S2 ESP32-S2
Hardware Configuration
Any analog sensor (e.g. Truebner SMT50 or SparkFun SEN-13322) is connected.
Version
v2.0.14
IDE Name
ArduinoIDE
Operating System
macOS 14.1.2
Flash frequency
80MHz
PSRAM enabled
yes
Upload speed
921600
Description
Expected behaviour:
When using ESP32-S2 and analogReadMilliVolts(pin) I should always get the measured voltage in milliVolts.
Weird behaviour: When changing the default 13 bit resolution of the ADC1 to e.g. 12bit using analogReadResolution(12); the outputs of analogReadMilliVolts(pin) are incorrect (half in size in case of 12bit).
Tried to track it down and found this to be happening (in esp32-hal-adc.c):
The __analogRead() function uses the 12 bit resolution (as expected because of analogReadResolution(12)). But __analogReadMilliVolts() internally also uses __analogRead() which returns a 12bit ADC value. But during transformation in esp_adc_cal_raw_to_voltage((uint32_t)adc_reading, &chars) the adc_reading is always expected to be the raw 13bit value in case of the ESP32-S2. There it assumes the 12 bit value to be 13 bit and the resulting value in milliVolts half of the correct value.
I assume this also happens with other chips than the S2, but haven't tested it so far.
Sketch
// Define the pin that the analog sensor is connected to (in my case A2 of the UM FeatherS2)
#define analogSensorPin A2
void setup() {
// initialize serial communication at 115200 bits per second:
Serial.begin(115200);
delay(1000);
// set the resolution to the 13 bits (0-8192) --> this is default, but just to make sure
analogReadResolution(13);
int analogValue = analogRead(analogSensorPin);
int analogVolts = analogReadMilliVolts(analogSensorPin);
Serial.printf("13 bit - ADC analog value = %d\n",analogValue);
Serial.printf("13 bit - ADC millivolts value = %d\n",analogVolts);
// set the resolution to 12 bits (0-4096)
analogReadResolution(12);
analogValue = analogRead(analogSensorPin);
analogVolts = analogReadMilliVolts(analogSensorPin);
Serial.printf("12 bit - ADC analog value = %d\n",analogValue);
Serial.printf("12 bit - ADC millivolts value = %d\n",analogVolts);
// set the resolution to 10 bits (0-1024)
analogReadResolution(10);
analogValue = analogRead(analogSensorPin);
analogVolts = analogReadMilliVolts(analogSensorPin);
Serial.printf("10 bit - ADC analog value = %d\n",analogValue);
Serial.printf("10 bit - ADC millivolts value = %d\n",analogVolts);
}
void loop() {
}Debug Message
Serial Output:
13 bit - ADC analog value = 2232
13 bit - ADC millivolts value = 711
12 bit - ADC analog value = 1104
12 bit - ADC millivolts value = 349
10 bit - ADC analog value = 278
10 bit - ADC millivolts value = 88
Other Steps to Reproduce
No response
I have checked existing issues, online documentation and the Troubleshooting Guide
- I confirm I have checked existing issues, online documentation and Troubleshooting guide.