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How to check the battery voltage

Due to the limitation of the number of pins in the ESP32C3, engineers had no extra pins to allocate to the battery for voltage measurement in order to ensure that the XIAO ESP32C3 has the same number of GPIOs as the other XIAO series available.

But if you prefer to use a separate pin for battery voltage measurement, you can refer to the genius operation of msfujino. We would also like to give a special thanks to msfujino for all the experience and efforts shared for the XIAO ESP32C3.

The basic operating idea is: The battery voltage was divided by 1/2 with 200k and connected to the A0 port so that the voltage could be monitored.

pir

The datasheet says nominally 2500mV full scale AD conversion, but there is a large variation from chip to chip, actually ±10%. My chip was 2700mV full scale.

Fortunately, the calibrated correction value for each chip is written in the fuse area, and by using the function alalogReadMilliVolts(), I can read the corrected voltage value without doing anything special.

The result of AD conversion and the voltage measured by the multimeter agree well with each other with an error of about 5 mV, which is not a problem in practical use.

In addition, during communication in particular, spike-like errors occurred, which had to be averaged out 16 times to remove them.

The following is the procedure to test the battery voltage.

void setup() {
  Serial.begin(115200);
  pinMode(A0, INPUT);         // ADC
}

void loop() {
  uint32_t Vbatt = 0;
  for(int i = 0; i < 16; i++) {
    Vbatt = Vbatt + analogReadMilliVolts(A0); // ADC with correction   
  }
  float Vbattf = 2 * Vbatt / 16 / 1000.0;     // attenuation ratio 1/2, mV --> V
  Serial.println(Vbattf, 3);
  delay(1000);
}
tip

The above is from Seeed Studio forum user msfujino, originally posted at: https://forum.seeedstudio.com/t/battery-voltage-monitor-and-ad-conversion-for-xiao-esp32c/267535. We recommend that you have good hands-on skills and better soldering skills before attempting to measure battery voltage based on the above, and be cautious of dangerous actions such as shorting out batteries.

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