PZEM-004T v3 with ESP32 DevKit V1 — Serial2 wiring and readings

The PZEM-004T v3.0 is a complete energy meter on a small board: it measures mains voltage, current (through its CT), power, energy, frequency and power factor, and sends the numbers over a 9600-baud TTL serial line. It is the standard part for home energy monitors and solar-export meters in India.

On the ESP32 DevKit V1, use the second hardware UART: RX2 (GPIO16) and TX2 (GPIO17), passed explicitly because core 3.x moved the defaults. The PZEM’s TX is a 5 V signal, so it goes through a 1 kΩ / 2 kΩ divider.

Everything on the L, N and CT side is 230 V and electrician-only. Only the four TTL pins are wired on the bench.

Wiring

Board quirks

• L, N and the CT are a 230 V installation. An electrician should wire L/N from an MCB- and RCCB-protected circuit and pass only the live wire through the CT, with the module in a closed box. You wire the four TTL pins, before mains is connected.
• The PZEM’s meter chip is powered from the mains side. With L/N unconnected it never replies, even though the TTL LEDs may light — so a bench test without mains always shows “No reply”.
• Arduino-ESP32 3.x moved the default Serial2 pins to RX 4 / TX 25. The library constructor takes the pins, so the sketch passes GPIO16 and GPIO17 (printed RX2 / TX2) explicitly.
• Many v3.0 boards also work with 3.3 V on the 5V pin (then no divider is needed), but not all of them — 5 V plus the divider works on every board.
• Energy (kWh) is stored inside the PZEM and survives power cuts. pzem.resetEnergy() clears it.
• The CT must clamp the live wire alone. Around a cable holding live and neutral, the currents cancel and it reads zero.

Code

// PZEM-004T v3.0 energy meter on an ESP32 DevKit V1 over Serial2 (Modbus-RTU, 9600 baud).
// Low-voltage side: 5V → VIN, GND → GND, PZEM TX → 1 kΩ/2 kΩ divider → RX2 (GPIO16), PZEM RX ← TX2 (GPIO17).
// L/N and the CT clamp are on 230 V — electrician only. The meter answers only while mains is connected.
#include <PZEM004Tv30.h>

constexpr uint8_t RX_PIN = 16, TX_PIN = 17;
// Name the pins: arduino-esp32 3.x would otherwise put Serial2 on RX 4 / TX 25.
PZEM004Tv30 pzem(Serial2, RX_PIN, TX_PIN);

void setup() {
  Serial.begin(115200);
  Serial.println("PZEM-004T v3.0 on Serial2 (RX2/TX2)");
}

void loop() {
  float v = pzem.voltage();
  if (isnan(v)) {
    Serial.println("No reply — is 230 V connected to L/N? Check TX/RX and the divider.");
  } else {
    Serial.printf("%.1f V  %.3f A  %.1f W  %.3f kWh  %.1f Hz  PF %.2f\n", v, pzem.current(), pzem.power(),
                  pzem.energy(), pzem.frequency(), pzem.pf());
  }
  delay(2000);
}

// PZEM-004T v3.0 energy meter on an ESP32 DevKit V1 over Serial2 (Modbus-RTU, 9600 baud).
// Low-voltage side: 5V → VIN, GND → GND, PZEM TX → 1 kΩ/2 kΩ divider → RX2 (GPIO16), PZEM RX ← TX2 (GPIO17).
// L/N and the CT clamp are on 230 V — electrician only. The meter answers only while mains is connected.
#include <PZEM004Tv30.h>

constexpr uint8_t RX_PIN = 16, TX_PIN = 17;
// Name the pins: arduino-esp32 3.x would otherwise put Serial2 on RX 4 / TX 25.
PZEM004Tv30 pzem(Serial2, RX_PIN, TX_PIN);

void setup() {
  Serial.begin(115200);
  Serial.println("PZEM-004T v3.0 on Serial2 (RX2/TX2)");
}

void loop() {
  float v = pzem.voltage();
  if (isnan(v)) {
    Serial.println("No reply — is 230 V connected to L/N? Check TX/RX and the divider.");
  } else {
    Serial.printf("%.1f V  %.3f A  %.1f W  %.3f kWh  %.1f Hz  PF %.2f\n", v, pzem.current(), pzem.power(),
                  pzem.energy(), pzem.frequency(), pzem.pf());
  }
  delay(2000);
}

Library: PZEM004Tv30 (Jakub Mandula) — compiled with PZEM004Tv30 1.2.1.

Expected serial output

PZEM-004T v3.0 on Serial2 (RX2/TX2)
231.4 V  0.412 A  61.8 W  12.347 kWh  50.0 Hz  PF 0.65
230.9 V  0.415 A  62.1 W  12.347 kWh  50.0 Hz  PF 0.65

PZEM-004T v3.0 on Serial2 (RX2/TX2)
231.4 V  0.412 A  61.8 W  12.347 kWh  50.0 Hz  PF 0.65
230.9 V  0.415 A  62.1 W  12.347 kWh  50.0 Hz  PF 0.65

Common errors