Documentation

// 3S Pack Voltage Monitor for Arduino
// Voltage divider: P+ -- 470k -- A0 -- 100k -- GND
// Max ADC voltage: 12.6V * (100 / 570) = 2.21V (safely under 5V)

const int adcPin = A0;
const float dividerRatio = (470.0 + 100.0) / 100.0;  // = 5.7
const float vRef = 5.0;

float pctFromVoltage(float v) {
  if (v >= 12.6) return 100.0;
  if (v <= 9.6) return 0.0;
  return ((v - 9.6) / (12.6 - 9.6)) * 100.0;
}

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

void loop() {
  int raw = analogRead(adcPin);
  float vAdc = (raw / 1023.0) * vRef;
  float vPack = vAdc * dividerRatio;

  Serial.print("Pack: ");
  Serial.print(vPack, 2);
  Serial.print(" V (");
  Serial.print(pctFromVoltage(vPack), 0);
  Serial.println(" %)");
  delay(1000);
}

// ESP32 reads 3S pack voltage through a 470k/100k divider on GPIO34
// 12.6V / 5.7 = 2.21V at ADC -- safely below 3.3V

const int adcPin = 34;
const float dividerRatio = (470.0 + 100.0) / 100.0;  // = 5.7
const float vRef = 3.3;

void setup() {
  Serial.begin(115200);
  analogReadResolution(12);
}

void loop() {
  int raw = analogRead(adcPin);
  float vAdc = (raw / 4095.0) * vRef;
  float vPack = vAdc * dividerRatio;
  Serial.printf("Pack: %.2f V\n", vPack);
  delay(1000);
}

#!/usr/bin/env python3
# Raspberry Pi has no built-in ADC -- use an MCP3008 or ADS1115.
# Example uses ADS1115 over I2C with a 470k/100k voltage divider.

import time
import board
import busio
import adafruit_ads1x15.ads1115 as ADS
from adafruit_ads1x15.analog_in import AnalogIn

i2c = busio.I2C(board.SCL, board.SDA)
ads = ADS.ADS1115(i2c)
chan = AnalogIn(ads, ADS.P0)

DIVIDER_RATIO = (470.0 + 100.0) / 100.0  # = 5.7

try:
    while True:
        v_adc = chan.voltage
        v_pack = v_adc * DIVIDER_RATIO
        print("Pack: {:.2f} V".format(v_pack))
        time.sleep(1)
except KeyboardInterrupt:
    print("Stopped")