Arduino-esp32: the analogRead seems doesn't work

[kedaya1999]

float sensor=25;
float gas_value;
void setup()
{
  pinMode(sensor,INPUT);
  Serial.begin(115200);
}

void loop()
{
  gas_value=analogRead(sensor);
  Serial.println(gas_value);
}

I connected my flame sensor, the results of serial output all show 4095

[me-no-dev]

try on pin above 32

[kedaya1999]

@me-no-dev Thank you for your suggestion, but after the replacement is the same, I just started using this development tool Can you give me a sample program with analogRead

[sctv]

What board are you using?

On 29 Sep 2017 14:31, "来搞破坏呀" [e-mail] wrote:

@me-no-dev https://github.com/me-no-dev Thank you for your suggestion,
but after the replacement is the same, I just started using this
development tool Can you give me a sample program with analogRead

—
You are receiving this because you are subscribed to this thread.
Reply to this email directly, view it on GitHub
https://github.com/espressif/arduino-esp32/issues/683#issuecomment-333126989,
or mute the thread
https://github.com/notifications/unsubscribe-auth/AAAVwidtbn5hZjBEIIf7G5wKJWCNhTeAks5snPFAgaJpZM4Poo2N
.

[kedaya1999]

@sctv i use nodemcu 32s

[lbernstone]

try using int instead of float. I'm surprised this doesn't give you an error on compile.

[radaiko]

I got the same problem with the WeMos Wifi Battery Board (Pocket 32 clone) on some pins I get always 4095 and on some I got always 0.

[vseven]

Try changing your resolution and attenuation:

analogReadResolution(11); // Default of 12 is not very linear. Recommended to use 10 or 11 depending on needed resolution.
analogSetAttenuation(ADC_6db); // Default is 11db which is very noisy. Recommended to use 2.5 or 6.

Also see this: https://www.esp32.com/viewtopic.php?f=19&t=2881&start=10#p13739

I've gotten pretty accurate analogReads using a HiLetGo NodeMCU ESP32s and the settings above.

[maza70]

in my project i had a range from 0-3V and then you need to set the right DB:
example code (i use the ESP32 adc library, Input is GPIO36 aka ADC1_CHANNEL_0 ):

#include <driver/adc.h>
int readLightSensor(){
  adc1_config_width(ADC_WIDTH_BIT_10);   //Range 0-1023 
  adc1_config_channel_atten(ADC1_CHANNEL_0,ADC_ATTEN_DB_11);  //ADC_ATTEN_DB_11 = 0-3,6V
  return adc1_get_raw( ADC1_CHANNEL_0 ); //Read analog
}

[everslick]

This issue is closed, because it looks as if it is not a bug or problem with the ESP32 Arduino core or its support libraries. For general API usage questions or help on specific coding challenges, please visit the arduino-esp32 Gitter channel. If you feel this issue was closed in error, reopen it and comment, why you think this is a bug in the Arduino-Core.

[thecvely]

The esp 32 integrates two 12-bit ACD registers. ADC1 whit 8 channels attached to GPIOs 32-39 ande ADC2 whit 10 channels in another pins. The thing is the ESP32 uses the ADC2 to manage wifi functions, so if you use Wifi, you can´t use that register.
See that here https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/peripherals/adc.html

[juliansantos]

Here it is the explanation to your problem.
https://docs.espressif.com/projects/esp-idf/en/latest/api-reference/peripherals/adc.html

[umartechboy]

ADC2 cannot be used if WiFi is enabled. See https://github.com/espressif/arduino-esp32/issues/440.
And, unfortunately, there is now work around YET.

Make sure your pin is not of ADC2