PZEM-004T v3 with Arduino Uno — mains power, energy and safe wiring

The PZEM-004T v3.0 is a complete single-phase energy meter on one board. It measures voltage, current, power, energy (kWh), frequency and power factor, and reports them over a serial link. For about ₹900 it is the basis of most DIY home-energy monitors in India.

On the Uno only the TTL side is your wiring: 5V, GND, and the serial lines to SoftwareSerial on D10/D11. The PZEM’s TX is pulled up to whatever feeds its 5V pin, so on a 5 V Uno it connects directly, with no divider. The mains side — L and N, and the current transformer clipped around the live wire — is electrician’s work, inside a closed enclosure.

The sketch uses the PZEM004Tv30 library and prints all six values every 2 seconds. It says clearly when the meter doesn’t answer, which on the bench (with no mains connected) is normal.

Wiring

Board quirks

• Electrician only for L, N and the CT. The PZEM measures voltage from its own L/N terminals, which carry 230 V, and its board is not touch-safe. Mount it in a closed enclosure on an MCB- and RCCB-protected circuit. The CT clips around the live wire of the load only — never both live and neutral, or it reads zero.
• The TTL side is opto-isolated, so the Uno never touches the mains — as long as you never connect the Uno’s GND to neutral.
• The PZEM only answers when its L/N side is powered from the mains. On USB alone it stays silent: “No reply” on the bench is expected.
• The Uno’s hardware serial is busy with USB, so the PZEM uses SoftwareSerial at 9600 baud, which is reliable at that speed.
• The energy counter (kWh) is stored inside the PZEM and survives power cuts. Reset it with pzem.resetEnergy() when you start a new month.
• Library Manager lists it as PZEM004Tv30 by Jakub Mandula.

Code

// PZEM-004T v3.0 energy meter on an Arduino Uno R3 (Modbus over SoftwareSerial).
// TTL side only: 5V → 5V, GND → GND, PZEM TX → D10 (Uno RX), PZEM RX ← D11 (Uno TX).
// L/N and the CT around the live wire are mains wiring - ELECTRICIAN ONLY.
#include <SoftwareSerial.h>
#include <PZEM004Tv30.h>

SoftwareSerial pzemSerial(10, 11);  // RX, TX
PZEM004Tv30 pzem(pzemSerial);

void setup() {
  Serial.begin(9600);
  Serial.println(F("PZEM-004T v3 on D10/D11"));
}

void loop() {
  float v = pzem.voltage();
  if (isnan(v)) {
    Serial.println(F("No reply - check TX/RX, 5V and that L/N are live"));
    delay(2000);
    return;
  }
  Serial.print(F("V "));
  Serial.print(v, 1);
  Serial.print(F("  A "));
  Serial.print(pzem.current(), 3);
  Serial.print(F("  W "));
  Serial.print(pzem.power(), 1);
  Serial.print(F("  kWh "));
  Serial.print(pzem.energy(), 3);
  Serial.print(F("  Hz "));
  Serial.print(pzem.frequency(), 1);
  Serial.print(F("  PF "));
  Serial.println(pzem.pf(), 2);
  delay(2000);
}

// PZEM-004T v3.0 energy meter on an Arduino Uno R3 (Modbus over SoftwareSerial).
// TTL side only: 5V → 5V, GND → GND, PZEM TX → D10 (Uno RX), PZEM RX ← D11 (Uno TX).
// L/N and the CT around the live wire are mains wiring - ELECTRICIAN ONLY.
#include <SoftwareSerial.h>
#include <PZEM004Tv30.h>

SoftwareSerial pzemSerial(10, 11);  // RX, TX
PZEM004Tv30 pzem(pzemSerial);

void setup() {
  Serial.begin(9600);
  Serial.println(F("PZEM-004T v3 on D10/D11"));
}

void loop() {
  float v = pzem.voltage();
  if (isnan(v)) {
    Serial.println(F("No reply - check TX/RX, 5V and that L/N are live"));
    delay(2000);
    return;
  }
  Serial.print(F("V "));
  Serial.print(v, 1);
  Serial.print(F("  A "));
  Serial.print(pzem.current(), 3);
  Serial.print(F("  W "));
  Serial.print(pzem.power(), 1);
  Serial.print(F("  kWh "));
  Serial.print(pzem.energy(), 3);
  Serial.print(F("  Hz "));
  Serial.print(pzem.frequency(), 1);
  Serial.print(F("  PF "));
  Serial.println(pzem.pf(), 2);
  delay(2000);
}

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

Expected serial output

PZEM-004T v3 on D10/D11
V 231.4  A 0.412  W 81.3  kWh 0.127  Hz 50.0  PF 0.85
V 231.2  A 0.415  W 81.9  kWh 0.127  Hz 50.0  PF 0.86

PZEM-004T v3 on D10/D11
V 231.4  A 0.412  W 81.3  kWh 0.127  Hz 50.0  PF 0.85
V 231.2  A 0.415  W 81.9  kWh 0.127  Hz 50.0  PF 0.86

Common errors