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carduinoesp32adc
Quang Minh Lê
Quang Minh Lê

Reputation: 169

Accuaracy problem with internal ADC in esp32

My circuit to measure battery right now is esp32, nrf24l01, and 18650. I powered up esp32 with 18650 3.6V nominal/4.2 max battery. Run a voltage divider 100k, 27k then it's 0.893V a measure point. At 3.6V measure point like ~0.72.

I use internal 1.1V ADC but why I only receive ~3V at monitor My circuit

float battery_read()
{
    //read battery voltage per %
    long sum = 0;                  // sum of samples taken
    float voltage = 0.0;           // calculated voltage
    float output = 0.0;            //output value
    const float battery_max = 4.2; //maximum voltage of battery
    const float battery_min = 3.0; //minimum voltage of battery before shutdown

    float R1 = 100000.0; // resistance of R1 (100K)
    float R2 = 27000.0;  // resistance of R2 (10K)

    for (int i = 0; i < 100; i++)
    {
        sum += adc1_get_voltage(ADC1_CHANNEL_0);
        delayMicroseconds(1000);
    }
    // calculate the voltage*/

    voltage = sum / (float)100;
    Serial.println(voltage);
    voltage = (voltage *1.1) / 2047.0; //for internal 1.1v reference
    // use if added divider circuit
    voltage = voltage / (R2/(R1+R2));

Upvotes: 0

Views: 1899

Answers (1)

Dark Sorrow
Dark Sorrow

Reputation: 1897

I am assuming you are using ESP32-WROOM-32 module.

Your register divider should be connected to SENSOR_VP (VP) pin if you wish to read from channel ADC1_CHANNEL_0 and not EN pin.

ADC1_CHANNEL_0 is mapped to SENSOR_VP (VP) pin.

Your EN pin should be to +3.3VDC through an RC network (R-> 10k and C-> 0.1uF). I doubt if your module is even booting as it is active high and needs 150uS delay before going high after every reset.

Make sure you execute adc1_config_width() and adc1_config_channel_atten() before the first time adc1_get_voltage() is called.

Upvotes: 1

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