Current, voltage and power

PZEM-004T with ESP32

One side of this board connects to mains voltage, so treat it with respect. Switch off the breaker before you touch the wiring, enclose the board, and use a fuse or breaker on the measured circuit. Users disagree about how well the two sides are isolated, and optocouplers on the serial lines do not by themselves prove the whole module is safe to touch, and forum posts question whether it meets safety standards, so assume the worst and keep it away from anything you touch. If you are not comfortable working on mains, have an electrician connect it. It suits a monitoring project, not billing.

In return, you get real numbers with little code. This page covers the 100 A version, which reads 80 to 260 V AC through an external clamp. The 10 A version looks similar but is wired differently: it has a built-in shunt, and the load current passes through the module itself, up to 10 A. Check which one you have. It reports voltage, current, power, energy, frequency and power factor over a serial link at 9600 baud, 8N1, using Modbus RTU. Put the clamp around one conductor only: around a whole cable, live and neutral cancel out and it reads zero. Do not swap in a different clamp without checking its ratio.

The logic side has 5V, RX, TX and GND. This port is passive: the 5V pin powers only its optocouplers, so all four wires are needed, and the measuring chip itself runs from the mains, so the module needs AC connected to answer at all. TX can reach 5 V, which is too much for an ESP32 pin, and the RX optocoupler expects a 5 V signal. So treat the two directions separately: one 74AHCT125 channel gives RX a clean 5 V signal, and a 10 kΩ and 20 kΩ divider brings TX down to about 3.3 V. Cheap bidirectional BSS138 boards are made mainly for I2C, so check one before you rely on it. Many display boards have only one spare UART, which may already be taken. Each module needs a unique Modbus address if you share the bus; the example uses the general address 0xF8, which works with one module only. This code reads the registers directly, with no library, and checks the Modbus CRC on every reply, so a corrupted frame is not shown as a reading.

Power and logic levels

5 V signal: needs a divider or level shifter

Supply	5 V logic side, mains on the other
Signal level	TX and RX are 5 V optocoupler lines
On an ESP32	Treat each direction separately: 74AHCT125 on RX, a divider on TX. Connect 5V and GND too.

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.

HardwareSerial pzem(1);
const int RX_PIN = 16, TX_PIN = 17;

uint16_t crc16(const uint8_t *b, size_t n) {   // Modbus CRC
  uint16_t c = 0xFFFF;
  while (n--) {
    c ^= *b++;
    for (int i = 0; i < 8; i++) c = (c & 1) ? (c >> 1) ^ 0xA001 : c >> 1;
  }
  return c;
}

uint32_t dword(const uint8_t *b) {     // low word comes first
  return (uint32_t)b[0] << 8 | b[1] | (uint32_t)b[2] << 24 | (uint32_t)b[3] << 16;
}

void setup() {
  Serial.begin(115200);
  pzem.begin(9600, SERIAL_8N1, RX_PIN, TX_PIN);
}

void loop() {
  uint8_t req[8] = {0xF8, 0x04, 0x00, 0x00, 0x00, 0x0A};   // 0xF8: one module only
  uint16_t c = crc16(req, 6);
  req[6] = c & 0xFF;
  req[7] = c >> 8;
  uint8_t r[25];
  while (pzem.available()) pzem.read();
  pzem.write(req, sizeof(req));
  if (pzem.readBytes(r, 25) == 25 && r[1] == 0x04 &&
      crc16(r, 23) == (uint16_t)(r[23] | r[24] << 8)) {
    Serial.printf("%.1f V  %.3f A  %.1f W  %.3f kWh  %.1f Hz  PF %.2f\n",
                  (r[3] << 8 | r[4]) / 10.0, dword(r + 5) / 1000.0, dword(r + 9) / 10.0,
                  dword(r + 13) / 1000.0, (r[17] << 8 | r[18]) / 10.0, (r[19] << 8 | r[20]) / 100.0);
  } else {
    Serial.println("No valid answer");
  }
  delay(2000);
}

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.