# analogRead too imprecise. ESP32

**URL:** <https://forum.arduino.cc/t/analogread-too-imprecise-esp32/1102215>\
**Category:** General Guidance\
**Created:** [March 15, 2023, 11:08am UTC](https://forum.arduino.cc/t/analogread-too-imprecise-esp32/1102215 "2023-03-15T11:08:39Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![kapi2454](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/kapi2454/32/474376_2.png) [@kapi2454](https://forum.arduino.cc/u/kapi2454)\
**Post date:** [March 15, 2023, 11:08am UTC](https://forum.arduino.cc/t/analogread-too-imprecise-esp32/1102215/1 "2023-03-15T11:08:39Z")

</div>

Hi people, how are you? I need some help.

```cpp
void setup() {
  // initialize serial communication at 115200 bits per second:
  Serial.begin(115200);
  
  //set the resolution to 12 bits (0-4096)
  analogReadResolution(10);
}

void loop() {
  // read the analog / millivolts value for pin 2:
  int analogValue = analogRead(2);
  int analogVolts = analogReadMilliVolts(2);
  
  // print out the values you read:
  Serial.printf("ADC analog value = %d\n",analogValue);
  Serial.printf("ADC millivolts value = %d\n",analogVolts);
  
  delay(1000); // delay in between reads for clear read from serial
}

```

I had that simple code, i wat to sense the Volts of a solar panel. In and Out.  
I let you a log to see my problem

```cpp
ADC millivolts value = 2269
ADC analog value = 1023
ADC millivolts value = 2295
ADC analog value = 647
ADC millivolts value = 2233
ADC analog value = 635
ADC millivolts value = 2009
ADC analog value = 645
ADC millivolts value = 2226
ADC analog value = 635
ADC millivolts value = 2262
ADC analog value = 650
ADC millivolts value = 2305
ADC analog value = 652
ADC millivolts value = 2249
ADC analog value = 652

```

I nedd to sense form 24V to 19V aprox.  
I make a this circuit (voltage divider)

[Voltage Divider](https://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.allaboutcircuits.com%2Ftools%2Fvoltage-divider-calculator%2F&psig=AOvVaw3DURnhUxggXlxOy7f7Hp1h&ust=1678964643963000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCNDV3Ovk3f0CFQAAAAAdAAAAABAE)

And the problem is the precision of analog Input of ESP32. It var from 600 to 652, it's imposible make a measure with this numbers.  
I check the input and it's constant, I use a regulated power supply, and a battery, then a put a filter. It's look like the problem is the input of ESP32. All of them are equals? May be this is a bad quality ESP32?

[This is mine ESP32](https://raw.githubusercontent.com/AchimPieters/esp32-homekit-camera/master/Images/ESP32-30PIN-DEVBOARD.png)

---

<div class="post-metadata">

**Author:** ![b707](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/b707/32/854321_2.png) [@b707](https://forum.arduino.cc/u/b707)\
**Post date:** [March 15, 2023, 11:19am UTC](https://forum.arduino.cc/t/analogread-too-imprecise-esp32/1102215/2 "2023-03-15T11:19:14Z")

</div>

> [@kapi2454](#):
>
> I check the input and it's constant

The result also depend on stability of esp32 power

---

<div class="post-metadata">

**Author:** ![Idahowalker](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/idahowalker/32/238858_2.png) [@Idahowalker](https://forum.arduino.cc/u/Idahowalker)\
**Post date:** [March 15, 2023, 11:22am UTC](https://forum.arduino.cc/t/analogread-too-imprecise-esp32/1102215/3 "2023-03-15T11:22:11Z")

</div>

```cpp
#include <driver/adc.h>

void setup()
{
  eg = xEventGroupCreate(); // get an event group handle
  x_message.topic.reserve(100);
  adc1_config_width(ADC_WIDTH_12Bit);
  adc1_config_channel_atten(ADC1_CHANNEL_6, ADC_ATTEN_DB_11);// using GPIO 34 wind direction
  adc1_config_channel_atten(ADC1_CHANNEL_3, ADC_ATTEN_DB_11);// using GPIO 39 current
  adc1_config_channel_atten(ADC1_CHANNEL_0, ADC_ATTEN_DB_11);// using GPIO 36 battery volts

}

void fReadBattery( void * parameter )
{
  const float r1 = 50500.0f; // R1 in ohm, 50K
  const float r2 = 10000.0f; // R2 in ohm, 10k potentiometer
  const TickType_t xFrequency = 1000; //delay for mS
  float adcValue = 0.0f;
  float Vbatt = 0.0f;
  int printCount = 0;
  float vRefScale = (3.3f / 4096.0f) * ((r1 + r2) / r2);
  uint64_t TimePastKalman = esp_timer_get_time(); // used by the Kalman filter UpdateProcessNoise, time since last kalman calculation
  SimpleKalmanFilter KF_ADC_b( 1.0f, 1.0f, .01f );
  TickType_t xLastWakeTime = xTaskGetTickCount();
  for (;;)
  {
    adc1_get_raw(ADC1_CHANNEL_0); //read and discard
    adcValue = float( adc1_get_raw(ADC1_CHANNEL_0) ); //take a raw ADC reading
    KF_ADC_b.setProcessNoise( (esp_timer_get_time() - TimePastKalman) / 1000000.0f ); //get time, in microsecods, since last readings
    adcValue = KF_ADC_b.updateEstimate( adcValue ); // apply simple Kalman filter
    Vbatt = adcValue * vRefScale;
    xSemaphoreTake( sema_CalculatedVoltage, portMAX_DELAY );
    CalculatedVoltage = Vbatt;
    xSemaphoreGive( sema_CalculatedVoltage );
    
      printCount++;
      if ( printCount == 3 )
      {
      //log_i( "Vbatt %f", Vbatt );
      printCount = 0;
      }
    
    TimePastKalman = esp_timer_get_time(); // time of update complete
    xLastWakeTime = xTaskGetTickCount();
    vTaskDelayUntil( &xLastWakeTime, xFrequency );
    //log_i( "fReadBattery %d", uxTaskGetStackHighWaterMark( NULL ) );
  }
  vTaskDelete( NULL );
}

```

is how I do it.

I use a 10K for R2 and this site for proper resistor value calculation, [Voltage Divider Calculator](https://ohmslawcalculator.com/voltage-divider-calculator).

As a note pin 2 on a ESP32 is not an analog pin for ADC1.

---

<div class="post-metadata">

**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\
**Post date:** [September 11, 2023, 11:22am UTC](https://forum.arduino.cc/t/analogread-too-imprecise-esp32/1102215/4 "2023-09-11T11:22:33Z")

</div>

This topic was automatically closed 180 days after the last reply. New replies are no longer allowed.