Documentation

// 351015 LiPo cell voltage monitor for Arduino Uno / Nano (5V, 10-bit ADC)
// Wiring: Cell (+) -- 100k -- A0 -- 100k -- GND
// Divider ratio = 0.5, so multiply ADC voltage x 2 to get cell voltage.

const int BAT_PIN   = A0;
const float VREF    = 5.0;     // 5V Arduino reference
const float DIVIDER = 2.0;     // (R1 + R2) / R2 with R1 = R2 = 100k

float readCellVoltage() {
  long sum = 0;
  for (int i = 0; i < 16; i++) {       // average 16 samples to reduce noise
    sum += analogRead(BAT_PIN);
    delay(2);
  }
  float adc = sum / 16.0;
  float vpin = (adc / 1023.0) * VREF;
  return vpin * DIVIDER;
}

int stateOfCharge(float v) {
  // Rough linear SoC map for 1S LiPo (3.0V empty, 4.2V full)
  float pct = (v - 3.0) / (4.2 - 3.0) * 100.0;
  if (pct < 0)   pct = 0;
  if (pct > 100) pct = 100;
  return (int)pct;
}

void setup() {
  Serial.begin(9600);
}

void loop() {
  float v = readCellVoltage();
  int   soc = stateOfCharge(v);
  Serial.print("Cell: ");
  Serial.print(v, 2);
  Serial.print(" V  (");
  Serial.print(soc);
  Serial.println("%)");

  if (v < 3.1) Serial.println("WARNING: cell near empty - stop discharge.");
  delay(2000);
}

// 351015 LiPo cell voltage monitor for ESP32
// Wiring: Cell (+) -- 100k -- GPIO34 -- 100k -- GND
// GPIO34 is an input-only ADC1 pin (safe for use during Wi-Fi).
// ESP32 ADC is nonlinear - we use analogReadMilliVolts() for a calibrated reading.

const int BAT_PIN   = 34;
const float DIVIDER = 2.0;     // R1 = R2 = 100k

float readCellVoltage() {
  uint32_t sumMv = 0;
  for (int i = 0; i < 32; i++) {
    sumMv += analogReadMilliVolts(BAT_PIN);  // returns calibrated mV
    delay(2);
  }
  float vpin = (sumMv / 32.0) / 1000.0;       // average, convert to volts
  return vpin * DIVIDER;
}

void setup() {
  Serial.begin(115200);
  analogSetPinAttenuation(BAT_PIN, ADC_11db); // ~0 - 3.3V input range
}

void loop() {
  float v = readCellVoltage();
  float soc = (v - 3.0) / 1.2 * 100.0;
  if (soc < 0)   soc = 0;
  if (soc > 100) soc = 100;

  Serial.printf("LiPo: %.2f V  (%.0f%%)\n", v, soc);
  if (v < 3.1) Serial.println("Low battery - going to deep sleep");
  delay(2000);
}

# 351015 LiPo cell voltage monitor for Raspberry Pi Pico (MicroPython)
# Wiring: Cell (+) -- 100k -- GP26/ADC0 -- 100k -- GND
# Pico ADC is 12-bit, 3.3V reference, exposed via machine.ADC().read_u16()

from machine import ADC, Pin
import time

adc = ADC(Pin(26))            # ADC0 on GP26
VREF    = 3.3
DIVIDER = 2.0                 # R1 = R2 = 100k

def read_cell_voltage():
    total = 0
    for _ in range(32):
        total += adc.read_u16()  # 0..65535
        time.sleep_ms(2)
    raw = total / 32
    vpin = (raw / 65535) * VREF
    return vpin * DIVIDER

def state_of_charge(v):
    pct = (v - 3.0) / 1.2 * 100
    return max(0, min(100, pct))

while True:
    v = read_cell_voltage()
    soc = state_of_charge(v)
    print("LiPo: {:.2f} V  ({:.0f}%)".format(v, soc))
    if v < 3.1:
        print("WARNING: cell near empty - stop discharge.")
    time.sleep(2)