Documentation

// TP4056 Cell Voltage Monitor for Arduino
// Connect OUT+ to a 100k/100k divider and read midpoint with A0

const int adcPin = A0;
const float dividerRatio = 2.0;
const float vRef = 5.0;

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

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

  Serial.print("Cell: ");
  Serial.print(vBat, 2);
  Serial.print(" V");

  if (vBat > 4.15) Serial.println(" -- FULL");
  else if (vBat > 3.7) Serial.println(" -- GOOD");
  else if (vBat > 3.3) Serial.println(" -- LOW");
  else Serial.println(" -- CRITICAL");

  delay(1000);
}

// ESP32 TP4056 monitor
// Cell voltage: OUT+ -- 220k -- GPIO34 -- 100k -- GND
// CHRG LED tap: GPIO32 (HIGH when charging)
// STDBY LED tap: GPIO33 (HIGH when full)
// Note: the LED pins on TP4056 are open-drain -- pull them up to 3.3V via 10k

const int adcPin = 34;
const int chrgPin = 32;
const int stdbyPin = 33;
const float dividerRatio = 3.2;
const float vRef = 3.3;

void setup() {
  Serial.begin(115200);
  pinMode(chrgPin, INPUT_PULLUP);
  pinMode(stdbyPin, INPUT_PULLUP);
  analogReadResolution(12);
}

void loop() {
  int raw = analogRead(adcPin);
  float vBat = (raw / 4095.0) * vRef * dividerRatio;

  bool charging = (digitalRead(chrgPin) == LOW);   // LED on = pin pulled low
  bool full     = (digitalRead(stdbyPin) == LOW);

  Serial.printf("Cell: %.2f V | Charging: %d | Full: %d\n", vBat, charging, full);
  delay(1500);
}

# Pico TP4056 voltage monitor
# Divider: OUT+ -- 100k -- GP26 (ADC0) -- 100k -- GND

from machine import ADC
import time

adc = ADC(0)
divider_ratio = 2.0
v_ref = 3.3

while True:
    raw = adc.read_u16()
    v_adc = (raw / 65535) * v_ref
    v_bat = v_adc * divider_ratio

    if v_bat > 4.15:
        state = "FULL"
    elif v_bat > 3.7:
        state = "GOOD"
    elif v_bat > 3.3:
        state = "LOW"
    else:
        state = "CRITICAL"

    print("Cell: {:.2f} V -- {}".format(v_bat, state))
    time.sleep(1)