See every watt your house is burning

How the measuring works

The PZEM-004T is a complete metering front-end: it samples mains voltage directly and current through the split-core CT clamp (clip it around the live wire — no rewiring), does the true-power maths on board, and hands the ESP clean numbers over UART. Your microcontroller never touches a dangerous analog signal — it just asks for V, A, W, kWh.

⚠ The mains-side rules

The measuring side of the PZEM connects to live AC — treat it with respect: everything lives in a closed junction box, the AC input goes through a 1 A fuse, all grounds are common, and the CT clamp's arrow (S1→S2) points with the current flow. Kill the breaker before touching anything on that side. If mains work isn't your thing, an electrician wires the box in ten minutes — the fun part is all on the low-voltage side.

The dashboard — tariff in, cost out

The pzem004t preset expands into the right widgets on its own; a number widget holds your tariff, and cost is one multiplication. The sketch below runs with no mains at all — RisalFakePower cycles a realistic household load so you can build and demo the whole meter on your desk:

#include <RisalUI.h>
#include <RisalFake.h>               // fake household load — test with no mains at all

RisalUI dash("Energy");
RisalFakePower meter;
float volts = 230, amps = 0, watts = 0, kwh = 0, pf = 0.9f, freq = 50, cost = 0;
int tariff = 12;                     // cents per kWh — tune it live

void setup() {
  dash.layout("Live", RICON_FLASH);
  dash.sensor("pzem004t", &volts, &amps, &watts, &kwh);  // V gauge · A · W chart · kWh
  dash.metric("Power factor", &pf);
  dash.stat("Cost", &cost, "$").decimals(2);
  dash.number("Tariff c/kWh", &tariff, 1, 100, 1);
  dash.beginAP("RisalDash-Power", "12345678");
}

void loop() {
  dash.update();
  meter.update();                    // appliances switch on/off, kWh accumulates
  volts = meter.voltage(); amps = meter.current(); watts = meter.power();
  kwh = meter.energy(); pf = meter.powerFactor();
  cost = kwh * tariff / 100.0f;
}

When the box is wired, swap the fake for the real reader — same variables, dashboard unchanged:

// The real reader — PZEM-004T V3 on Serial2 (library: mandulaj/PZEM-004T-v30).
#include <PZEM004Tv30.h>
PZEM004Tv30 pzem(Serial2, 16, 17);   // RX2, TX2

float v = pzem.voltage();
if (!isnan(v)) {                     // NaN = no reading — keep the last good value
  volts = v;
  amps  = pzem.current();
  watts = pzem.power();
  kwh   = pzem.energy();
  pf    = pzem.pf();
}

Both halves ship as library examples: examples/04_Templates/PowerMeter (the meter) and EnergyMonitor (kWh + cost + breaker toggle). Publish to MQTT and it lands in Home Assistant's energy panel automatically.

Bill of materials

Under $25 total — the commercial equivalents with an app start at several times that, and phone apps aside, this one's dashboard is served by the chip itself.