Current, voltage and power

TP4056 battery charger with ESP32

Do not connect a lithium cell straight to the 3V3 pin. A cell runs from about 4.2 V down to 3.0 V, which is too high when full and too low when empty, so a regulated 3.3 V rail is needed between them. A display board with a large backlight also pulls far more current than a bare ESP32, so test runtime on your real board. A TP4056 only handles charging.

Buy the module with protection, which has BAT and OUT terminals and a DW01 chip. It cuts off for over-discharge at around 2.5 V. That is too low to be a normal stopping point, so stop in software earlier, for example at 3.2 V, and put the board to sleep. The charge current is set by the PROG resistor: 1.2 kΩ gives about 1 A. Check that yours suits your cell. A small cell should not be charged at 1 A.

Using it while charging works on most boards, but load sharing is not a clean feature here, and forum users say to test your exact board. The load can confuse the charger's end-of-charge detection. Allow for USB current too, as the charger and the board both draw from it. To read the battery, use a divider from BAT+ to an ADC pin. Two equal resistors halve the voltage, so 4.2 V becomes 2.1 V, safely within range. High values cut the drain but load the ADC, so calibrate against a multimeter. Voltage is only a rough guide to charge left. LCD Ultra Pro can read an analog pin and show it on a bar or label without code. Use your measured empty and full values.

Power and logic levels

5 V signal: needs a divider or level shifter

Supply	5 V in, cell up to 4.2 V
Signal level	Cell voltage is above 3.3 V
On an ESP32	Use a divider to read the cell. Never connect BAT+ to a GPIO or 3V3.

ESP32 pins, including those on a display board's connectors, work at 3.3 V and are not 5 V tolerant. Modules differ, so if in doubt, measure the signal before you connect it.

const int ADC_PIN = 4;
const float DIVIDER = 2.0;            // two equal resistors
const float LOW_VOLTS = 3.2;          // stop before the DW01 cuts off

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

void loop() {
  long sum = 0;
  for (int i = 0; i < 32; i++) sum += analogReadMilliVolts(ADC_PIN);
  float volts = sum / 32.0 * DIVIDER / 1000.0;
  Serial.printf("Battery %.2f V\n", volts);
  if (volts < LOW_VOLTS) {
    Serial.println("Low battery: going to sleep");
    esp_deep_sleep_start();
  }
  delay(10000);
}

Use this information at your own risk. It is for general guidance only: the example code compiles, but it has not been tested on every part, and modules differ between sellers. Check the manufacturer's data before you build. Product names belong to their owners, and LCD Ultra Pro is not affiliated with them. See our Terms.