10 · Arduino Examples

This chapter collects complete, working Arduino sketches for typical rbAmp scenarios. All examples rely on the helpers introduced in 02_initialization.md.

These examples talk to rbAmp directly through the raw I2C register API. They are intended for native, embedded, or otherwise resource-constrained integrations where direct control is required and every byte on the bus matters.

For a more convenient, structured interface — use the rbamp Arduino library (see chapter 17 · Arduino Library). The library wraps the register-level details behind a high-level RbAmp class with named methods (readVoltage(), latchPeriod(), readPeriodSnapshot(), etc.), an automatic per-channel Wh accumulator, application-level NACK retry + sanity-check discipline for ESP32 targets, and multi-module helpers (see the bus-timing and retry guidance in chapter 3 · API Reference). Most user-facing projects should start from the library and fall back to the raw API only when needed.

Examples table of contents

#	Title	Difficulty	Display / Output	MQTT	DRDY	Multi-module	Bidirectional	Use case
1	Quick read	minimal	Serial	—	—	—	—	Smoke test
2	60-second energy meter on OLED	low	OLED	—	—	—	—	Boxed Wh counter
3	Multi-module monitor	low	Serial	—	—	yes (3)	—	Whole-home monitoring
4	Per-appliance energy tracker (UI3)	medium	—	yes	—	—	—	Sub-metering in HA
5	Master-side bidirectional accounting on a BASIC module	medium	Serial	—	yes	—	yes (master)	Solar home on BASIC tier
6	Home energy balance	high	—	yes	—	yes (3)	yes	Full home balance
7	Power-event detection	medium	Serial + SD	—	yes	—	—	Appliance event log
8	MQTT publisher with HA Auto-discovery	medium	—	yes (+disco)	—	—	optional	Drop-in HA integration
9	Battery-powered remote logger with deep sleep	medium	—	yes	—	—	—	Off-grid / outdoor meter
10	Time-of-use (TOU) tariff with NTP wall-clock	medium	Serial	yes	—	—	optional	Peak / off-peak tariff metering

Common header for all examples

Each example assumes the following helper definitions are present in the file. To save space, the block is not repeated in each sketch below — assume it is included.

cpp

#include <Wire.h>
/**
 * @brief  Read one byte from a register of an rbAmp slave.
 * @param  addr 7-bit I2C slave address.
 * @param  reg  Register address inside the slave.
 * @return Register value.
 */
uint8_t rb_read_u8(uint8_t addr, uint8_t reg) {
  Wire.beginTransmission(addr);
  Wire.write(reg);
  // Return 0 (not 0xFF) on NACK so bit-flags like DATA_VALID/PERIOD_VALID
  // are not falsely read as "valid" when the slave is unreachable.
  if (Wire.endTransmission(false) != 0) return 0;   // NACK on address/data
  if (Wire.requestFrom(addr, (uint8_t)1) != 1) return 0;
  return Wire.read();
}
/**
 * @brief  Read a little-endian float32 from four consecutive registers.
 * @details rbAmp supports READ auto-increment (burst-read is valid). The
 *          per-byte form below is shown for clarity; production code may
 *          prefer a single burst-read for atomicity (see chapter 11).
 * @param  addr 7-bit I2C slave address.
 * @param  reg  Address of the LSB of the 4-byte float.
 * @return Reconstructed IEEE-754 single-precision value.
 */
float rb_read_float_le(uint8_t addr, uint8_t reg) {
  uint8_t buf[4];
  for (int i = 0; i < 4; i++) buf[i] = rb_read_u8(addr, reg + i);
  float f;
  memcpy(&f, buf, 4);                          // host is little-endian (AVR/ESP/ARM)
  return f;
}
/**
 * @brief  Write a single byte to a register of an rbAmp slave.
 * @param  addr 7-bit I2C slave address.
 * @param  reg  Target register address.
 * @param  val  Byte to write.
 */
void rb_write_u8(uint8_t addr, uint8_t reg, uint8_t val) {
  Wire.beginTransmission(addr);
  Wire.write(reg);
  Wire.write(val);
  Wire.endTransmission();
}
/**
 * @brief  Broadcast CMD_LATCH_PERIOD to every rbAmp on the bus that has
 *         GC reception enabled (FLEET_CONFIG.bit0 = 1; opt-in, default OFF).
 * @details Canonical 5-byte general-call frame: A5 27 group tick_lo tick_hi.
 *          Slaves reject any first byte != 0xA5. See chapter 11 §6.3.2.
 * @param  tick16  Caller's 16-bit window counter — mirrored at GC_TICK
 *                 (0x59) for missed-frame detection.
 * @param  group   GROUP_ID filter (0 = all-call; otherwise must match
 *                 the module's REG_GROUP_ID = 0x28).
 * @return true on ACK (at least one slave accepted the frame).
 *         false on bus-level NACK — no module on the bus has GC enabled
 *         (or no module is in the group). Caller MUST fall back to
 *         per-module sequential CMD_LATCH_PERIOD.
 */
bool rb_broadcast_latch(uint16_t tick16, uint8_t group = 0) {
  Wire.beginTransmission(0x00);                // I2C general call
  Wire.write(0xA5);                            // frame magic
  Wire.write(0x27);                            // CMD_LATCH_PERIOD opcode
  Wire.write(group);                           // group_id
  Wire.write((uint8_t)(tick16 & 0xFF));        // tick_lo
  Wire.write((uint8_t)((tick16 >> 8) & 0xFF)); // tick_hi
  return Wire.endTransmission() == 0;
}

Example 1 — Quick read (minimal)

Goal: print current U, I, P, PF to Serial every second. Hardware: ESP32 / Arduino + one rbAmp UI1.

cpp

#define RB_ADDR 0x50
void setup() {
  Serial.begin(115200);
  Wire.begin();
  Wire.setClock(50000);
  delay(300);                                  // let the module finish booting
  // Wait until the first RT window has been computed (DATA_VALID bit 0).
  while ((rb_read_u8(RB_ADDR, 0xCE) & 0x01) == 0) delay(50);
  Serial.println("rbAmp ready");
}
void loop() {
  // Real-time block at 0x86..0xBD is refreshed every ~200 ms by the module.
  float u  = rb_read_float_le(RB_ADDR, 0x86);  // RMS voltage,   V
  float i  = rb_read_float_le(RB_ADDR, 0x8E);  // RMS current,   A
  float p  = rb_read_float_le(RB_ADDR, 0xA6);  // active power,  W (signed)
  float pf = rb_read_float_le(RB_ADDR, 0xB2);  // power factor,  −1..+1 (signed)
  Serial.printf("U=%.1fV  I=%.3fA  P=%+.1fW  PF=%+.3f\n", u, i, p, pf);
  delay(1000);
}

Expected output:

plaintext

rbAmp ready
U=230.1V  I=0.262A  P=+60.2W  PF=+0.998
U=229.9V  I=0.262A  P=+60.1W  PF=+0.998
...

Example 2 — 60-second energy meter on OLED

Goal: Wh counter refreshed once per minute, shown on a 128×64 OLED. Hardware: ESP32 + rbAmp + SSD1306 OLED on the same I2C bus. Accounting: unidirectional (BASIC tier).

cpp

#include <Adafruit_SSD1306.h>
#define RB_ADDR 0x50
#define OLED_W 128
#define OLED_H 64
Adafruit_SSD1306 oled(OLED_W, OLED_H, &Wire);
uint32_t t_prev_ms = 0;                        // wall-clock at last latch
double total_wh = 0;                           // accumulated energy, Wh
void setup() {
  Serial.begin(115200);
  Wire.begin();
  delay(300);
  oled.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  // Wait DATA_VALID, then issue a primer latch (its result is discarded).
  while ((rb_read_u8(RB_ADDR, 0xCE) & 0x01) == 0) delay(50);
  rb_write_u8(RB_ADDR, 0x01, 0x27);            // CMD_LATCH_PERIOD — primer
  t_prev_ms = millis();
}
void loop() {
  delay(60000);                                // 60-second period
  // 1) Final latch — closes the period [t_prev_ms .. now].
  rb_write_u8(RB_ADDR, 0x01, 0x27);
  uint32_t t_now_ms = millis();
  delay(50);                                   // let firmware finalise the snapshot
  // 2) Verify the snapshot is fresh before using it.
  if ((rb_read_u8(RB_ADDR, 0x07) & 0x01) == 0) {
    Serial.println("WARN: stale snapshot");
    t_prev_ms = millis();
    return;
  }
  // 3) Read time-averaged power for channel 0 (PERIOD_AVG_P_W[0]).
  float avg_p = rb_read_float_le(RB_ADDR, 0xDC);
  // 4) Compute energy using the MASTER clock (authoritative).
  float dt_s = (t_now_ms - t_prev_ms) / 1000.0f;
  double e_wh = (double)avg_p * dt_s / 3600.0;
  total_wh += e_wh;
  t_prev_ms = t_now_ms;
  // 5) Update the OLED.
  oled.clearDisplay();
  oled.setTextSize(1);
  oled.setTextColor(SSD1306_WHITE);
  oled.setCursor(0, 0);
  oled.printf("P:  %6.1f W", avg_p);
  oled.setCursor(0, 16);
  oled.printf("dt: %6.1f s", dt_s);
  oled.setCursor(0, 32);
  oled.setTextSize(2);
  oled.printf("%.2f Wh", total_wh);
  oled.display();
  Serial.printf("avg_P=%.1f  E_period=%.3f  total=%.3f\n", avg_p, e_wh, total_wh);
}

The OLED shares the rbAmp I2C bus (typical OLED address is 0x3C, no collision with 0x50).

Example 3 — Multi-module monitor

Goal: poll three modules (main feed, water heater, AC), print total power. Hardware: ESP32 + 3 × rbAmp UI1 (addresses 0x50, 0x51, 0x52).

cpp

const uint8_t modules[] = {0x50, 0x51, 0x52};
const char* labels[]    = {"Mains ", "Boiler", "AC    "};
const int N = 3;
void setup() {
  Serial.begin(115200);
  Wire.begin();
  Wire.setClock(50000);
  delay(300);
  // Bus scan — confirm every module is present.
  for (int i = 0; i < N; i++) {
    Wire.beginTransmission(modules[i]);
    if (Wire.endTransmission() != 0) {
      Serial.printf("ERROR: %s at 0x%02X not found — restarting in 5 s\n",
                    labels[i], modules[i]);
      delay(5000);
      ESP.restart();                           // reboot rather than hang
    }
  }
  Serial.println("All modules OK");
}
void loop() {
  float total_p = 0;
  Serial.println("---");
  // Read each module in turn (round-robin).
  for (int i = 0; i < N; i++) {
    float u = rb_read_float_le(modules[i], 0x86);
    float p = rb_read_float_le(modules[i], 0xA6);
    Serial.printf("[%s] U=%.1f  P=%+.1f W\n", labels[i], u, p);
    total_p += p;
  }
  Serial.printf("TOTAL: %.1f W\n", total_p);
  delay(2000);
}

Example 4 — Per-appliance energy tracker (UI3)

Goal: a UI3 module with three CT clamps on three different single-phase loads. Independent Wh counters per load. MQTT publishing. Hardware: ESP32 + 1 × rbAmp UI3. Accounting: unidirectional.

cpp

#include <WiFi.h>
#include <PubSubClient.h>
#define RB_ADDR 0x50
const char* CH_NAMES[3] = {"main", "heatpump", "lights"};
WiFiClient espClient;
PubSubClient mqtt(espClient);
uint32_t t_prev_ms = 0;
double total_wh[3] = {0, 0, 0};                 // per-channel accumulated energy
/**
 * @brief  Publish a single channel's data to MQTT.
 * @param  ch_name   Channel name (used in the topic).
 * @param  avg_p     Time-averaged power over the latched period, W.
 * @param  e_wh      Accumulated channel energy, Wh.
 */
void mqtt_publish(const char* ch_name, float avg_p, double e_wh) {
  char topic[64], payload[64];
  snprintf(topic, sizeof(topic), "rbamp/%s/state", ch_name);
  snprintf(payload, sizeof(payload),
           "{\"power\":%.1f,\"energy\":%.4f}", avg_p, e_wh);
  mqtt.publish(topic, payload);
}
void setup() {
  Serial.begin(115200);
  WiFi.begin("ssid", "password");
  uint32_t wifi_start = millis();
  while (WiFi.status() != WL_CONNECTED) {        // bounded wait — avoid WDT
    delay(500);
    if (millis() - wifi_start > 30000) {
      Serial.println("WiFi timeout — restarting");
      ESP.restart();
    }
  }
  mqtt.setServer("192.168.1.10", 1883);
  mqtt.setKeepAlive(60);                         // 60 s keepalive (default 15 s)
  mqtt.connect("rbamp-ui3");                     // best-effort; loop() retries
  Wire.begin();
  delay(300);
  while ((rb_read_u8(RB_ADDR, 0xCE) & 0x01) == 0) delay(50);
  rb_write_u8(RB_ADDR, 0x01, 0x27);             // primer latch
  t_prev_ms = millis();
}
void loop() {
  // Service MQTT keepalive every iteration (not once per 60 s — broker would
  // drop the session after the default 15 s timeout). Reconnect with bounded
  // back-off when the broker is unreachable.
  if (!mqtt.connected()) {
    static uint32_t last_retry = 0;
    if (millis() - last_retry > 5000) {
      last_retry = millis();
      mqtt.connect("rbamp-ui3");
    }
  }
  mqtt.loop();
  // Non-blocking 60-second period — keeps mqtt.loop alive for keepalive.
  static uint32_t last_period_ms = 0;
  if (last_period_ms == 0) last_period_ms = millis();
  if (millis() - last_period_ms < 60000) {
    delay(50);
    return;
  }
  last_period_ms = millis();
  // Latch + read three per-channel period averages.
  rb_write_u8(RB_ADDR, 0x01, 0x27);
  uint32_t t_now = millis();
  delay(50);
  if ((rb_read_u8(RB_ADDR, 0x07) & 0x01) == 0) {
    t_prev_ms = millis();
    return;
  }
  // Per-channel PERIOD_AVG_P_W: I0 at 0xDC, I1 at 0xC2, I2 at 0xC6.
  float avg_p[3];
  avg_p[0] = rb_read_float_le(RB_ADDR, 0xDC);   // I0
  avg_p[1] = rb_read_float_le(RB_ADDR, 0xC2);   // I1
  avg_p[2] = rb_read_float_le(RB_ADDR, 0xC6);   // I2
  float dt_s = (t_now - t_prev_ms) / 1000.0f;
  t_prev_ms = t_now;
  for (int ch = 0; ch < 3; ch++) {
    double e = (double)avg_p[ch] * dt_s / 3600.0;
    total_wh[ch] += e;
    Serial.printf("[%s] avg_P=%+.1f W  E_total=%.3f Wh\n",
                  CH_NAMES[ch], avg_p[ch], total_wh[ch]);
    mqtt_publish(CH_NAMES[ch], avg_p[ch], total_wh[ch]);
  }
}

Example 5 — Master-side bidirectional accounting on a BASIC module

Goal: implement bidirectional accounting on the master when the module's tier is BASIC (period accumulator clamps negative samples). The master reads RT P_real every ~200 ms and separates consumption / export itself. Hardware: ESP32 + rbAmp UI1 on a load with a solar inverter. Applicability: for BASIC owners who need export visibility. Slightly lower accuracy than a true STANDARD / PRO module, but works today.

cpp

#define RB_ADDR 0x50
const int PIN_DRDY = 15;
volatile bool data_ready = false;               // set by DRDY ISR
double e_consumed_wh = 0;
double e_exported_wh = 0;
uint32_t t_last_sample_ms = 0;
/**
 * @brief  Interrupt service routine for DRDY falling edge.
 * @details Marks fresh data available. Kept tiny (no I2C calls inside ISR).
 */
void IRAM_ATTR on_drdy() { data_ready = true; }
void setup() {
  Serial.begin(115200);
  Wire.begin();
  pinMode(PIN_DRDY, INPUT_PULLUP);
  delay(300);
  // Wait for the slave to come online BEFORE arming the ISR — otherwise a
  // settling pull-up edge can fire a spurious interrupt against a not-yet-
  // initialised slave and set data_ready before the first valid window.
  while ((rb_read_u8(RB_ADDR, 0xCE) & 0x01) == 0) delay(50);
  t_last_sample_ms = millis();
  attachInterrupt(digitalPinToInterrupt(PIN_DRDY), on_drdy, FALLING);
  Serial.println("Bidirectional accumulator started");
}
void loop() {
  if (!data_ready) return;                      // sleep until next RT window
  data_ready = false;
  uint32_t t_now = millis();
  // Signed instantaneous P_real: positive = consume, negative = export.
  float p = rb_read_float_le(RB_ADDR, 0xA6);
  float dt_s = (t_now - t_last_sample_ms) / 1000.0f;
  t_last_sample_ms = t_now;
  // Split into two accumulators on the master side.
  if (p > 0) {
    e_consumed_wh += p * dt_s / 3600.0;
  } else {
    e_exported_wh += (-p) * dt_s / 3600.0;
  }
  // Print summary every 5 seconds (not on every RT window).
  static uint32_t last_print = 0;
  if (t_now - last_print >= 5000) {
    last_print = t_now;
    Serial.printf("P=%+8.1fW   consumed=%.4f Wh  exported=%.4f Wh  net=%+.4f Wh\n",
                  p, e_consumed_wh, e_exported_wh,
                  e_consumed_wh - e_exported_wh);
  }
}

Notes:

DRDY synchronises reads with each RT window (~200 ms).
Accuracy depends on DRDY interval stability (typically ±1 ms).
A small error accumulates near P zero-crossings but is negligible for household loads.

Example 6 — Home energy balance

Goal: full balance dashboard. Three modules:

rbAmp #1 on the main feed (mains): bidirectional — measures grid in / out.
rbAmp #2 on the solar inverter output (solar): measures generation.
rbAmp #3 UI3 on three large loads (heat pump, AC, EV charger).

The master computes: total_consumed = solar_self_used + grid_consumed, solar_generated = solar_self_used + grid_exported.

Hardware: ESP32 + 3 × rbAmp + WiFi + MQTT. Tiers: STANDARD or PRO product tier for the mains module (bidirectional). Solar and Loads modules can be BASIC (unidirectional by construction).

cpp

#include <WiFi.h>
#include <PubSubClient.h>
const uint8_t ADDR_MAINS = 0x50;                // bidirectional (STANDARD/PRO)
const uint8_t ADDR_SOLAR = 0x51;                // generation only (BASIC OK)
const uint8_t ADDR_LOADS = 0x52;                // UI3, big consumers
// PERIOD_AVG_P_NEG address for the mains module — see the SKU datasheet
// of the STANDARD / PRO product. Set to 0xFF on BASIC modules.
#define REG_PERIOD_AVG_P_NEG_MAINS 0xFF
WiFiClient espClient;
PubSubClient mqtt(espClient);
uint32_t t_prev_ms = 0;
/** Accumulated energy in Wh, per category. */
struct {
  double mains_in_wh    = 0;                    // grid consumed
  double mains_out_wh   = 0;                    // grid exported
  double solar_total_wh = 0;                    // solar generated
  double loads_wh[3]    = {0, 0, 0};            // per-appliance
} totals;
void setup() {
  Serial.begin(115200);
  WiFi.begin("ssid", "password");
  while (WiFi.status() != WL_CONNECTED) delay(500);
  mqtt.setServer("192.168.1.10", 1883);
  mqtt.connect("home-balance");
  Wire.begin();
  Wire.setClock(50000);
  delay(300);
  // Wait until all three modules report DATA_VALID.
  for (uint8_t addr : {ADDR_MAINS, ADDR_SOLAR, ADDR_LOADS}) {
    while ((rb_read_u8(addr, 0xCE) & 0x01) == 0) delay(50);
  }
  static uint16_t gc_tick = 0;
  if (!rb_broadcast_latch(gc_tick++)) {
    // GC NACK — no module has GC enabled. Fall back to per-module latch.
    for (uint8_t addr : {ADDR_MAINS, ADDR_SOLAR, ADDR_LOADS}) {
      rb_write_u8(addr, 0x01, 0x27);
    }
  }
  t_prev_ms = millis();
  Serial.println("Home balance started");
}
void loop() {
  delay(60000);
  // Synchronous latch — all three modules snapshot at the same instant.
  static uint16_t gc_tick = 1;
  if (!rb_broadcast_latch(gc_tick++)) {
    // GC NACK — fall back to per-module sequential latch (skew ~1 ms/module).
    for (uint8_t addr : {ADDR_MAINS, ADDR_SOLAR, ADDR_LOADS}) {
      rb_write_u8(addr, 0x01, 0x27);
    }
  }
  uint32_t t_now = millis();
  delay(50);
  float dt_s = (t_now - t_prev_ms) / 1000.0f;
  t_prev_ms = t_now;
  // ----- MAINS (bidirectional, STANDARD/PRO tier) -----
  if (rb_read_u8(ADDR_MAINS, 0x07) & 0x01) {
    float avg_p_consume = rb_read_float_le(ADDR_MAINS, 0xDC);
    float avg_p_export  = (REG_PERIOD_AVG_P_NEG_MAINS != 0xFF)
        ? rb_read_float_le(ADDR_MAINS, REG_PERIOD_AVG_P_NEG_MAINS)
        : 0.0f;
    totals.mains_in_wh  += avg_p_consume * dt_s / 3600.0;
    totals.mains_out_wh += avg_p_export  * dt_s / 3600.0;
  }
  // ----- SOLAR (generation only) -----
  // The CT arrow points toward the home; P > 0 = inverter exporting.
  if (rb_read_u8(ADDR_SOLAR, 0x07) & 0x01) {
    float avg_p = rb_read_float_le(ADDR_SOLAR, 0xDC);
    totals.solar_total_wh += avg_p * dt_s / 3600.0;
  }
  // ----- LOADS (UI3, three channels) -----
  if (rb_read_u8(ADDR_LOADS, 0x07) & 0x01) {
    float p[3];
    p[0] = rb_read_float_le(ADDR_LOADS, 0xDC);  // I0 channel
    p[1] = rb_read_float_le(ADDR_LOADS, 0xC2);  // I1 channel
    p[2] = rb_read_float_le(ADDR_LOADS, 0xC6);  // I2 channel
    for (int i = 0; i < 3; i++) totals.loads_wh[i] += p[i] * dt_s / 3600.0;
  }
  // Derived balance figures.
  double total_consumed  = totals.mains_in_wh + totals.solar_total_wh
                         - totals.mains_out_wh;
  double solar_self_used = totals.solar_total_wh - totals.mains_out_wh;
  if (solar_self_used < 0) solar_self_used = 0;  // clamp measurement noise
  Serial.printf("MAINS  in=%.2f  out=%.2f\n", totals.mains_in_wh, totals.mains_out_wh);
  Serial.printf("SOLAR  gen=%.2f  self-used=%.2f  exported=%.2f\n",
                totals.solar_total_wh, solar_self_used, totals.mains_out_wh);
  Serial.printf("LOADS  HP=%.2f  AC=%.2f  EV=%.2f\n",
                totals.loads_wh[0], totals.loads_wh[1], totals.loads_wh[2]);
  Serial.printf("TOTAL  household consumed=%.2f Wh\n", total_consumed);
  // Publish the entire balance to a single MQTT topic (retained).
  char payload[512];
  snprintf(payload, sizeof(payload),
    "{\"mains_in\":%.3f,\"mains_out\":%.3f,\"solar\":%.3f,"
    "\"self_used\":%.3f,\"total_consumed\":%.3f,"
    "\"hp\":%.3f,\"ac\":%.3f,\"ev\":%.3f}",
    totals.mains_in_wh, totals.mains_out_wh, totals.solar_total_wh,
    solar_self_used, total_consumed,
    totals.loads_wh[0], totals.loads_wh[1], totals.loads_wh[2]);
  mqtt.publish("home/energy/balance", payload, true);
  mqtt.loop();
}

Notes:

rb_broadcast_latch(tick) ensures all three modules snapshot at the same instant — critical for an accurate balance. GC reception is opt-in per module (FLEET_CONFIG.bit0, default OFF, see chapter 02). If the GC frame NACKs, the example falls back to per-module sequential CMD_LATCH_PERIOD (skew ~1 ms per module on 50 kHz).
solar_self_used = solar_total − exported_to_grid — the energy generated and locally consumed.
total_consumed = mains_in + solar_self_used — total household consumption.

Example 7 — Power-event detection

Goal: on every RT window (200 ms), compare P against an exponentially-weighted moving average (EMA). Log significant deviations to an SD card. Hardware: ESP32 + rbAmp + SD card. Use case: automatic detection of large-load events (microwave, AC, kettle) turning on or off.

cpp

#include <SD.h>
#define RB_ADDR 0x50
const int PIN_DRDY  = 15;
const int PIN_SD_CS = 5;
volatile bool data_ready = false;
float p_ema = 0;                                // exponential moving average
const float EMA_ALPHA = 0.05;                   // ~4 s time constant at 5 Hz updates
const float EVENT_THRESHOLD_W = 200.0;          // ignore steps below this
File logfile;
/** @brief  DRDY interrupt — only sets a flag. */
void IRAM_ATTR on_drdy() { data_ready = true; }
void setup() {
  Serial.begin(115200);
  Wire.begin();
  pinMode(PIN_DRDY, INPUT_PULLUP);
  // SD card setup with explicit failure check — opening a non-existent file
  // returns a falsey File object; writing to it is undefined on some cores.
  if (!SD.begin(PIN_SD_CS)) {
    Serial.println("ERROR: SD.begin() failed — restarting in 5 s");
    delay(5000);
    ESP.restart();
  }
  logfile = SD.open("/events.log", FILE_APPEND);
  if (!logfile) {
    Serial.println("ERROR: SD.open(events.log) failed — restarting in 5 s");
    delay(5000);
    ESP.restart();
  }
  delay(300);
  while ((rb_read_u8(RB_ADDR, 0xCE) & 0x01) == 0) delay(50);
  // Seed the EMA with the current power so we do not log a spurious startup event.
  p_ema = rb_read_float_le(RB_ADDR, 0xA6);
  attachInterrupt(digitalPinToInterrupt(PIN_DRDY), on_drdy, FALLING);
  Serial.println("Event detector started");
}
void loop() {
  if (!data_ready) return;
  data_ready = false;
  // Compute the deviation from the running average.
  float p = rb_read_float_le(RB_ADDR, 0xA6);
  float delta = p - p_ema;
  p_ema = (1 - EMA_ALPHA) * p_ema + EMA_ALPHA * p;
  // Log when the deviation exceeds the threshold.
  if (fabsf(delta) > EVENT_THRESHOLD_W) {       // fabsf for float (avoids double promotion)
    const char* type = (delta > 0) ? "TURN_ON" : "TURN_OFF";
    char line[128];
    snprintf(line, sizeof(line),
             "%lu  %s  delta=%+.1f W  P=%.1f W  EMA=%.1f W\n",
             millis(), type, delta, p, p_ema);
    Serial.print(line);
    logfile.print(line);
    logfile.flush();                            // ensure the line hits the card
  }
}

Notes:

The EMA adapts to background load in ~4 s — it does not react to slow drifts.
A 200 W threshold skips minor loads (lights, phone chargers) and catches major appliances.
DRDY provides precise synchronisation with each P_real update.

Example 8 — MQTT publisher with Home Assistant Auto-discovery

RESULT screenshot for the MQTT + Home Assistant auto-discovery example: the rbAmp energy dashboard in HA. REUSE existing render (Odoo attachment 7922 png / 7923 webp). Applies across all platform example chapters (12-16).

Goal: a drop-in HA integration. The ESP32 connects to WiFi and an MQTT broker, publishes Home Assistant auto-discovery configs (so the entities appear in HA without any YAML), and emits a JSON state every minute. No HA YAML changes are needed. Hardware: ESP32 + one rbAmp UI1 + WiFi network with an MQTT broker (Mosquitto, EMQX, HA Mosquitto add-on, etc.). Accounting: unidirectional. Replace the period registers with the bidirectional ones for STANDARD / PRO modules.

cpp

#include <WiFi.h>
#include <PubSubClient.h>
#define RB_ADDR 0x50
const char* WIFI_SSID    = "ssid";
const char* WIFI_PASS    = "password";
const char* MQTT_HOST    = "192.168.1.10";
const uint16_t MQTT_PORT = 1883;
const char* MQTT_USER    = "ha";                // optional, NULL to disable
const char* MQTT_PASS    = "secret";
// Stable identifiers — the HA discovery topic must be unique per entity.
const char* DEVICE_ID    = "rbamp_main";
const char* DEVICE_NAME  = "Mains rbAmp";
WiFiClient   espClient;
PubSubClient mqtt(espClient);
uint32_t t_prev_ms = 0;
double total_wh = 0;                            // accumulated energy
/**
 * @brief  Publish a single HA discovery config for one sensor.
 * @param  key          Short key used in topic and value_template.
 * @param  friendly     Friendly name shown in HA.
 * @param  unit         Unit of measurement (e.g. "V", "W", "Wh"). NULL = none.
 * @param  device_class HA device_class string (e.g. "voltage"). NULL = none.
 * @param  state_class  HA state_class ("measurement" / "total_increasing").
 * @details The config topic is retained, so HA discovers the entity even
 *          after a restart without waiting for the next state publish.
 */
void publish_discovery_sensor(const char* key,
                              const char* friendly,
                              const char* unit,
                              const char* device_class,
                              const char* state_class) {
  char topic[128];
  char payload[512];
  snprintf(topic, sizeof(topic),
           "homeassistant/sensor/%s/%s/config", DEVICE_ID, key);
  // Build the discovery JSON. The shared "device" block ties all entities
  // to one device card in HA.
  int n = snprintf(payload, sizeof(payload),
    "{"
      "\"name\":\"%s %s\","
      "\"unique_id\":\"%s_%s\","
      "\"state_topic\":\"rbamp/%s/state\","
      "\"value_template\":\"{{ value_json.%s }}\","
      "\"state_class\":\"%s\","
      "\"device\":{"
        "\"identifiers\":[\"%s\"],"
        "\"name\":\"%s\","
        "\"manufacturer\":\"rbAmp\","
        "\"model\":\"rbAmp UI*\""
      "}",
    DEVICE_NAME, friendly,
    DEVICE_ID, key,
    DEVICE_ID,
    key,
    state_class,
    DEVICE_ID, DEVICE_NAME);
  // Append optional fields.
  if (unit && n < (int)sizeof(payload)) {
    n += snprintf(payload + n, sizeof(payload) - n,
                  ",\"unit_of_measurement\":\"%s\"", unit);
  }
  if (device_class && n < (int)sizeof(payload)) {
    n += snprintf(payload + n, sizeof(payload) - n,
                  ",\"device_class\":\"%s\"", device_class);
  }
  if (n < (int)sizeof(payload) - 1) {           // guard against overflow underflow
    snprintf(payload + n, sizeof(payload) - n, "}");
  } else {
    payload[sizeof(payload) - 2] = '}';         // forced close on truncation
    payload[sizeof(payload) - 1] = '\0';
    Serial.println("WARN: HA discovery payload truncated");
  }
  mqtt.publish(topic, payload, true);           // retained — survives broker restart
}
/**
 * @brief  Publish the full HA Auto-discovery set for one rbAmp module.
 * @details Call once on every (re)connect to the broker.
 */
void publish_discovery_all() {
  publish_discovery_sensor("voltage",      "Voltage",       "V",  "voltage",      "measurement");
  publish_discovery_sensor("current",      "Current",       "A",  "current",      "measurement");
  publish_discovery_sensor("power",        "Power",         "W",  "power",        "measurement");
  publish_discovery_sensor("energy",       "Energy",        "Wh", "energy",       "total_increasing");
  publish_discovery_sensor("frequency",    "Frequency",     "Hz", "frequency",    "measurement");
  publish_discovery_sensor("power_factor", "Power Factor",  NULL, "power_factor", "measurement");
  publish_discovery_sensor("apparent_power", "Apparent Power", "VA",  "apparent_power", "measurement");
  publish_discovery_sensor("reactive_power", "Reactive Power", "var", "reactive_power", "measurement");
}
/**
 * @brief  Try to (re)connect to the MQTT broker once.
 * @return true on success, false otherwise. Caller is responsible for retry
 *         pacing — this function NEVER blocks longer than the underlying
 *         PubSubClient.connect() timeout.
 * @details Republishes discovery configs on every successful reconnect.
 *          Replaces the previous unbounded `while (!connected) delay(2000)`
 *          loop which would trip the ESP32 task watchdog after ~5 s of broker
 *          unavailability.
 */
bool mqtt_try_connect() {
  if (mqtt.connected()) return true;
  Serial.print("MQTT connecting... ");
  bool ok = MQTT_USER
      ? mqtt.connect(DEVICE_ID, MQTT_USER, MQTT_PASS)
      : mqtt.connect(DEVICE_ID);
  if (ok) {
    Serial.println("OK");
    publish_discovery_all();
  } else {
    Serial.printf("failed rc=%d (will retry)\n", mqtt.state());
  }
  return ok;
}
void setup() {
  Serial.begin(115200);
  // 1) WiFi — bounded wait, restart on persistent failure (avoids WDT).
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  uint32_t wifi_start = millis();
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    if (millis() - wifi_start > 30000) {
      Serial.println("WiFi timeout — restarting");
      ESP.restart();
    }
  }
  Serial.printf("WiFi up, IP=%s\n", WiFi.localIP().toString().c_str());
  // 2) MQTT.
  mqtt.setServer(MQTT_HOST, MQTT_PORT);
  mqtt.setKeepAlive(60);                        // 60 s keepalive (default 15 s)
  mqtt.setBufferSize(1024);                     // big enough for one discovery payload
  // 3) rbAmp.
  Wire.begin();
  Wire.setClock(50000);
  delay(300);
  while ((rb_read_u8(RB_ADDR, 0xCE) & 0x01) == 0) delay(50);
  rb_write_u8(RB_ADDR, 0x01, 0x27);             // primer latch
  t_prev_ms = millis();
  // 4) First MQTT attempt — failure is non-fatal, loop() will retry.
  mqtt_try_connect();
}
void loop() {
  // Keep the broker session alive: service mqtt.loop() every iteration and
  // attempt reconnect with bounded back-off (no blocking 2s delay).
  if (!mqtt.connected()) {
    static uint32_t last_retry = 0;
    if (millis() - last_retry > 5000) {         // retry at most every 5 s
      last_retry = millis();
      mqtt_try_connect();
    }
  }
  mqtt.loop();
  static uint32_t last_period = 0;
  if (last_period == 0) last_period = millis(); // seed on first iteration
  if (millis() - last_period < 60000) {
    delay(50);                                  // short slice — keeps loop responsive
    return;
  }
  last_period = millis();
  // ----- Latch + read period snapshot -----
  rb_write_u8(RB_ADDR, 0x01, 0x27);
  uint32_t t_now = millis();
  delay(50);
  if ((rb_read_u8(RB_ADDR, 0x07) & 0x01) == 0) {
    Serial.println("WARN: stale snapshot, skipping publish");
    t_prev_ms = millis();
    return;
  }
  float avg_p = rb_read_float_le(RB_ADDR, 0xDC);
  float dt_s  = (t_now - t_prev_ms) / 1000.0f;
  total_wh += (double)avg_p * dt_s / 3600.0;
  t_prev_ms = t_now;
  // ----- Read live RT values -----
  float u  = rb_read_float_le(RB_ADDR, 0x86);
  float i  = rb_read_float_le(RB_ADDR, 0x8E);
  float pf = rb_read_float_le(RB_ADDR, 0xB2);
  float q  = rb_read_float_le(RB_ADDR, 0xD0);
  uint8_t freq = rb_read_u8(RB_ADDR, 0x20);
  // ----- Compose the state JSON -----
  char payload[384];
  snprintf(payload, sizeof(payload),
    "{"
      "\"voltage\":%.1f,"
      "\"current\":%.3f,"
      "\"power\":%.1f,"
      "\"energy\":%.3f,"
      "\"frequency\":%u,"
      "\"power_factor\":%.3f,"
      "\"apparent_power\":%.1f,"
      "\"reactive_power\":%.1f"
    "}",
    u, i, avg_p, total_wh,
    (unsigned)freq, pf, u * i, q);
  // Topic shape matches the value_template of every discovery config.
  char topic[64];
  snprintf(topic, sizeof(topic), "rbamp/%s/state", DEVICE_ID);
  mqtt.publish(topic, payload, false);          // state is fresh each period, not retained
  Serial.printf("Published: %s\n", payload);
}

Result in Home Assistant:

Within seconds of the first publish, HA auto-creates a device called Mains rbAmp with 8 entities (Voltage, Current, Power, Energy, Frequency, Power Factor, Apparent Power, Reactive Power).
The Energy entity has state_class: total_increasing and the right device_class, so HA's Energy dashboard accepts it as a consumption source.
To remove the entity from HA, publish an empty payload to its homeassistant/sensor/.../config topic (retained).

Extending:

For multi-channel UI2/UI3, repeat the discovery block with suffixed keys (current_1, power_1, energy_1, …) and add those fields to the state JSON.
For bidirectional STANDARD / PRO modules, add energy_exported with device_class: energy and state_class: total_increasing.

Example 9 — Battery-powered remote logger with deep sleep

Goal: an outdoor / off-grid energy logger that wakes every 10 minutes, latches a period, publishes the data, and goes back to deep sleep. Average current consumption a couple of mA, so a single Li-ion cell lasts many months. Hardware: ESP32 (or ESP32-S3) + one rbAmp UI1 + a small Li-ion battery + WiFi. The rbAmp is also kept under a low-quiescent LDO so its ~15 mA consumption only occurs during wake. Accounting: unidirectional. Energy is preserved across deep-sleep cycles via RTC slow-memory.

cpp

#include <WiFi.h>
#include <PubSubClient.h>
#include "esp_sleep.h"
#define RB_ADDR 0x50
const char* WIFI_SSID = "ssid";
const char* WIFI_PASS = "password";
const char* MQTT_HOST = "192.168.1.10";
// Wake every 10 minutes (600 s). The interval is the master_dt for Wh.
const uint64_t SLEEP_US = 10ULL * 60ULL * 1000000ULL;
// Power for rbAmp can be gated through a MOSFET driven by a GPIO,
// or simply left always-on if the LDO quiescent is acceptable.
const int PIN_RBAMP_POWER = 4;
// Values that must survive deep sleep are placed in RTC slow memory.
// IMPORTANT: ESP32 RTC slow memory is NOT zeroed on power-on after a brown-out
// or PSU dropout — it may hold garbage that looks like valid state. Gate every
// retained variable through a magic-marker check on cold boot.
RTC_DATA_ATTR uint32_t rtc_magic         = 0;   // 0xCAFEFEED when state initialised
RTC_DATA_ATTR double   rtc_total_wh      = 0;
RTC_DATA_ATTR uint32_t rtc_wake_count    = 0;
RTC_DATA_ATTR bool     rtc_primer_done   = false;
RTC_DATA_ATTR uint64_t rtc_t_prev_us     = 0;   // boot-time wall-clock anchor
#define RTC_MAGIC 0xCAFEFEEDu
WiFiClient   espClient;
PubSubClient mqtt(espClient);
/**
 * @brief  Power rbAmp on/off via a GPIO-driven high-side switch.
 * @param  on  true = enable, false = disable.
 * @details If your hardware always-powers rbAmp, you can remove this function
 *          and skip the calls to it.
 */
void rbamp_power(bool on) {
  pinMode(PIN_RBAMP_POWER, OUTPUT);
  digitalWrite(PIN_RBAMP_POWER, on ? HIGH : LOW);
  if (on) delay(300);                           // boot time
}
/**
 * @brief  Bring up WiFi with a hard timeout, so deep-sleep is never blocked
 *         forever on a missing AP.
 * @param  timeout_ms  Maximum time to wait for an association.
 * @return true on success, false on timeout.
 */
bool wifi_connect(uint32_t timeout_ms) {
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  uint32_t t0 = millis();
  while (WiFi.status() != WL_CONNECTED) {
    if (millis() - t0 > timeout_ms) return false;
    delay(100);
  }
  return true;
}
/**
 * @brief  Publish one measurement to MQTT.
 * @param  avg_p   Time-averaged power over the last interval, W.
 * @param  total_e Accumulated energy total, Wh.
 * @param  dt_s    Length of the elapsed interval, seconds.
 */
void publish_measurement(float avg_p, double total_e, float dt_s) {
  char payload[256];
  snprintf(payload, sizeof(payload),
    "{\"wake\":%lu,\"dt_s\":%.1f,\"avg_p\":%.1f,\"energy_wh\":%.3f}",
    (unsigned long)rtc_wake_count, dt_s, avg_p, total_e);
  mqtt.publish("rbamp/remote/state", payload, true);
  mqtt.loop();
  Serial.printf("Published: %s\n", payload);
}
void setup() {
  Serial.begin(115200);
  // --- Cold-boot detection ---
  // On any non-deep-sleep reset (power-on, brown-out, watchdog, ESP.restart),
  // RTC slow memory may contain garbage. Initialise on first boot.
  if (rtc_magic != RTC_MAGIC) {
    Serial.println("Cold boot — initialising RTC state");
    rtc_total_wh    = 0.0;
    rtc_wake_count  = 0;
    rtc_primer_done = false;
    rtc_t_prev_us   = 0;
    rtc_magic       = RTC_MAGIC;
  }
  rtc_wake_count++;
  // --- Power up rbAmp and bring up I2C ---
  rbamp_power(true);
  Wire.begin();
  Wire.setClock(50000);
  while ((rb_read_u8(RB_ADDR, 0xCE) & 0x01) == 0) delay(50);
  // First wake-up after a cold boot: do a primer latch (its result is discarded).
  if (!rtc_primer_done) {
    rb_write_u8(RB_ADDR, 0x01, 0x27);
    rtc_t_prev_us = esp_timer_get_time();
    rtc_primer_done = true;
    // Go straight back to sleep — we need at least one full period to elapse
    // before the next latch can produce a meaningful sample.
    Serial.println("Primer done — sleeping until first real period");
    rbamp_power(false);
    esp_sleep_enable_timer_wakeup(SLEEP_US);
    esp_deep_sleep_start();
  }
  // --- Subsequent wake-ups: read the period that just ended ---
  rb_write_u8(RB_ADDR, 0x01, 0x27);             // close current period
  uint64_t t_now_us = esp_timer_get_time();
  delay(50);
  if ((rb_read_u8(RB_ADDR, 0x07) & 0x01) == 0) {
    Serial.println("WARN: stale snapshot — skipping this cycle");
    rtc_t_prev_us = t_now_us;
    rbamp_power(false);
    esp_sleep_enable_timer_wakeup(SLEEP_US);
    esp_deep_sleep_start();
  }
  float avg_p = rb_read_float_le(RB_ADDR, 0xDC);
  // dt is wall-clock between latches; we measure it on the ESP32's RTC.
  // SLEEP_US is the intent; esp_timer accounts for actual sleep + on-time.
  float dt_s = (float)(t_now_us - rtc_t_prev_us) / 1000000.0f;
  rtc_t_prev_us = t_now_us;
  // Accumulate energy in RTC memory so it survives sleep.
  rtc_total_wh += (double)avg_p * dt_s / 3600.0;
  // --- Publish via WiFi/MQTT ---
  if (wifi_connect(8000)) {
    mqtt.setServer(MQTT_HOST, 1883);
    mqtt.setBufferSize(512);
    if (mqtt.connect("rbamp-remote")) {
      publish_measurement(avg_p, rtc_total_wh, dt_s);
      mqtt.disconnect();
    }
    WiFi.disconnect(true);
    WiFi.mode(WIFI_OFF);
  } else {
    Serial.println("WiFi failed — value buffered in RTC memory, will retry next wake");
  }
  // --- Sleep ---
  rbamp_power(false);                           // power-gate rbAmp
  esp_sleep_enable_timer_wakeup(SLEEP_US);
  Serial.println("Deep sleep");
  esp_deep_sleep_start();
}
void loop() {
  // setup() always ends in esp_deep_sleep_start() — loop is never reached.
}

Power budget (typical, ESP32-WROOM):

Awake duration per wake: ~3 s (Wi-Fi + MQTT + I2C).
Wake current: ~80 mA average → ~0.07 mAh per wake.
Sleep current: ~10 µA (RTC + retained domains).
One wake every 10 min → ~10 mAh/day total → a single 2000 mAh Li-ion cell lasts ~6 months.

Notes:

rtc_total_wh survives deep sleep via RTC_DATA_ATTR. It is lost on full power loss (battery removed). For ultimate persistence, periodically commit the value to MQTT or to NVS.
The primer-latch step is gated by rtc_primer_done, so the first sample after a cold boot is correctly discarded.
wifi_connect() has a hard timeout. If WiFi is unavailable, the sketch goes back to sleep — the energy total keeps accumulating internally and is published on the next successful connection.

Example 10 — Time-of-use (TOU) tariff with NTP wall-clock

Goal: bill energy under a time-of-use schedule (different rates during peak and off-peak hours). The ESP32 keeps a real wall-clock via NTP, splits each latched period into the right tariff bucket, resets daily totals at midnight, and publishes MQTT payloads with ISO timestamps. Hardware: ESP32 + one rbAmp UI1 + WiFi. Accounting: unidirectional. The same bucket logic works for STANDARD / PRO tiers — just feed both the consumption and the export accumulators through it.

cpp

#include <WiFi.h>
#include <PubSubClient.h>
#include <time.h>
#define RB_ADDR 0x50
const char* WIFI_SSID = "ssid";
const char* WIFI_PASS = "password";
const char* MQTT_HOST = "192.168.1.10";
// NTP. Use a regional pool, then fall back to a global pool.
const char* NTP_PRIMARY   = "pool.ntp.org";
const char* NTP_SECONDARY = "time.google.com";
// Local timezone in POSIX TZ format. Example: Central Europe (Berlin / Warsaw).
//   CET = standard offset +1, CEST = daylight offset +2,
//   M3.5.0/2 = last Sunday of March 02:00 → DST starts,
//   M10.5.0/3 = last Sunday of October 03:00 → DST ends.
const char* TZ_INFO = "CET-1CEST,M3.5.0/2,M10.5.0/3";
// Time-of-use schedule: peak hours [PEAK_START_HOUR .. PEAK_END_HOUR), local time.
const int PEAK_START_HOUR = 8;   // inclusive
const int PEAK_END_HOUR   = 22;  // exclusive
WiFiClient   espClient;
PubSubClient mqtt(espClient);
uint32_t t_prev_ms = 0;
/** @brief  Energy totals for the current day, split by tariff. */
struct DayTotals {
  double peak_wh     = 0;   // Wh consumed during peak hours
  double off_peak_wh = 0;   // Wh consumed during off-peak hours
  int    day_of_year = -1;  // tm_yday of the day these totals belong to
};
DayTotals today;
/** @brief  Lifetime totals, never reset by the daily roll-over. */
struct LifetimeTotals {
  double peak_wh     = 0;
  double off_peak_wh = 0;
};
LifetimeTotals lifetime;
/**
 * @brief  Connect to WiFi (blocking with progress dots on Serial).
 */
void wifi_connect() {
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASS);
  Serial.print("WiFi");
  while (WiFi.status() != WL_CONNECTED) { delay(500); Serial.print('.'); }
  Serial.printf(" up, IP=%s\n", WiFi.localIP().toString().c_str());
}
/**
 * @brief  Synchronise the system clock with NTP and apply the local timezone.
 * @details Blocks until the first valid time is received (timeout 15 s).
 *          On timeout the function returns anyway; subsequent reads will see
 *          tm_year == (1970-1900) and the caller can detect this.
 */
void ntp_sync() {
  configTime(0, 0, NTP_PRIMARY, NTP_SECONDARY);   // raw UTC first
  setenv("TZ", TZ_INFO, 1);                       // then apply local TZ
  tzset();
  Serial.print("NTP sync");
  time_t now = 0;
  uint32_t t0 = millis();
  while (now < 1700000000 && millis() - t0 < 15000) {  // sanity: ≥ year 2023
    delay(500);
    Serial.print('.');
    time(&now);
  }
  struct tm tm_now;
  localtime_r(&now, &tm_now);
  Serial.printf(" %04d-%02d-%02d %02d:%02d:%02d %s\n",
                tm_now.tm_year + 1900, tm_now.tm_mon + 1, tm_now.tm_mday,
                tm_now.tm_hour, tm_now.tm_min, tm_now.tm_sec, tm_now.tm_zone);
}
/**
 * @brief  Decide whether a given local hour falls inside the peak tariff window.
 * @param  hour  Hour of day, 0..23 (local time).
 * @return true if peak, false if off-peak.
 * @details For schedules that span midnight (e.g. peak is 22..6),
 *          swap the test to `(hour >= PEAK_START_HOUR || hour < PEAK_END_HOUR)`.
 */
bool is_peak_hour(int hour) {
  return (hour >= PEAK_START_HOUR && hour < PEAK_END_HOUR);
}
/**
 * @brief  Format the current local time as ISO 8601 (with offset).
 * @param  out      Destination buffer.
 * @param  out_len  Buffer size.
 */
void format_iso_now(char* out, size_t out_len) {
  time_t now;
  time(&now);
  struct tm tm_now;
  localtime_r(&now, &tm_now);
  strftime(out, out_len, "%Y-%m-%dT%H:%M:%S%z", &tm_now);  // e.g. 2026-05-22T18:30:00+0200
}
/**
 * @brief  Add the latched energy of one period to the right tariff bucket,
 *         and roll the daily totals over at midnight.
 * @param  e_wh    Energy accumulated during the period, Wh.
 * @param  tm_now  Local time at the moment of the latch (NOT at period start).
 */
void accumulate_energy(double e_wh, const struct tm& tm_now) {
  // Daily roll-over: when the day changes, publish yesterday's totals
  // (if any) and reset.
  if (today.day_of_year != tm_now.tm_yday) {
    if (today.day_of_year >= 0) {
      char payload[192];
      snprintf(payload, sizeof(payload),
        "{\"yday\":%d,\"peak_wh\":%.3f,\"off_peak_wh\":%.3f,\"total_wh\":%.3f}",
        today.day_of_year,
        today.peak_wh, today.off_peak_wh,
        today.peak_wh + today.off_peak_wh);
      mqtt.publish("rbamp/tou/day_close", payload, true);
      Serial.printf("Day closed: %s\n", payload);
    }
    today = {};                                  // reset
    today.day_of_year = tm_now.tm_yday;
  }
  // Add to the right bucket. The choice is made on the latch instant —
  // accurate enough at 60 s periods (boundary error < 60 s/day).
  if (is_peak_hour(tm_now.tm_hour)) {
    today.peak_wh    += e_wh;
    lifetime.peak_wh += e_wh;
  } else {
    today.off_peak_wh    += e_wh;
    lifetime.off_peak_wh += e_wh;
  }
}
/**
 * @brief  Publish one tariff-tagged state to MQTT.
 * @param  iso     ISO 8601 timestamp of the measurement.
 * @param  avg_p   Time-averaged power over the just-closed period, W.
 * @param  e_wh    Energy added to the totals in this period, Wh.
 * @param  peak    true if the current hour is a peak hour.
 */
void publish_state(const char* iso, float avg_p, double e_wh, bool peak) {
  char payload[384];
  snprintf(payload, sizeof(payload),
    "{"
      "\"ts\":\"%s\","
      "\"tariff\":\"%s\","
      "\"avg_p\":%.1f,"
      "\"period_wh\":%.4f,"
      "\"today_peak_wh\":%.3f,"
      "\"today_off_peak_wh\":%.3f,"
      "\"life_peak_wh\":%.3f,"
      "\"life_off_peak_wh\":%.3f"
    "}",
    iso, peak ? "peak" : "off_peak",
    avg_p, e_wh,
    today.peak_wh, today.off_peak_wh,
    lifetime.peak_wh, lifetime.off_peak_wh);
  mqtt.publish("rbamp/tou/state", payload, false);
  Serial.printf("%s\n", payload);
}
void setup() {
  Serial.begin(115200);
  // 1) WiFi and NTP — get the wall clock first.
  wifi_connect();
  ntp_sync();
  // 2) MQTT.
  mqtt.setServer(MQTT_HOST, 1883);
  mqtt.setKeepAlive(60);                         // 60 s keepalive (default 15 s)
  mqtt.setBufferSize(512);
  mqtt.connect("rbamp-tou");                     // best-effort; loop() retries
  // 3) rbAmp.
  Wire.begin();
  Wire.setClock(50000);
  delay(300);
  while ((rb_read_u8(RB_ADDR, 0xCE) & 0x01) == 0) delay(50);
  rb_write_u8(RB_ADDR, 0x01, 0x27);              // primer latch
  t_prev_ms = millis();
  Serial.printf("TOU started: peak %02d:00..%02d:00 local\n",
                PEAK_START_HOUR, PEAK_END_HOUR);
}
void loop() {
  // Maintain MQTT session: reconnect with bounded back-off (no blocking).
  if (!mqtt.connected()) {
    static uint32_t last_retry = 0;
    if (millis() - last_retry > 5000) {
      last_retry = millis();
      mqtt.connect("rbamp-tou");
    }
  }
  mqtt.loop();
  static uint32_t last_period = 0;
  if (last_period == 0) last_period = millis();  // seed on first iteration
  if (millis() - last_period < 60000) {
    delay(50);                                   // short slice — keeps mqtt.loop responsive
    return;
  }
  last_period = millis();
  // ----- Latch + period read -----
  rb_write_u8(RB_ADDR, 0x01, 0x27);
  uint32_t t_now_ms = millis();
  delay(50);
  if ((rb_read_u8(RB_ADDR, 0x07) & 0x01) == 0) {
    Serial.println("WARN: stale snapshot, skipping");
    t_prev_ms = millis();
    return;
  }
  float avg_p = rb_read_float_le(RB_ADDR, 0xDC);
  float dt_s  = (t_now_ms - t_prev_ms) / 1000.0f;
  double e_wh = (double)avg_p * dt_s / 3600.0;
  t_prev_ms = t_now_ms;
  // ----- Tag with current local time, choose tariff bucket -----
  time_t now_s;
  time(&now_s);
  struct tm tm_now;
  localtime_r(&now_s, &tm_now);
  // Guard against a fresh boot with no NTP yet (year << 2023).
  if (tm_now.tm_year + 1900 < 2023) {
    Serial.println("WARN: clock not yet synced, retrying NTP");
    ntp_sync();
    return;
  }
  accumulate_energy(e_wh, tm_now);
  char iso[40];
  format_iso_now(iso, sizeof(iso));
  publish_state(iso, avg_p, e_wh, is_peak_hour(tm_now.tm_hour));
}

Notes:

The chip never sees the wall clock. The master attaches the timestamp at the moment of the latch — that is the right moment, because that is when the measurement window closed.
localtime_r() automatically applies the POSIX TZ rule, so DST transitions are handled correctly without any extra code.
Boundary error: a 60 s period that crosses the 22:00 boundary is attributed entirely to off-peak (the timestamp is at the latch instant, after 22:00). For 60-second periods this is at most ~30 s of misattribution per day — negligible for residential billing. For 15-minute periods, prefer to align the latch to the schedule boundary, or split the period across both buckets.
For STANDARD / PRO bidirectional metering, run a second accumulate_energy() call on the export side and publish both peak/off-peak consumption and peak/off-peak export.
The daily roll-over publishes a retained rbamp/tou/day_close payload at midnight; Home Assistant or a Grafana data source can subscribe to it to record daily totals.

Sample MQTT state payload:

json

{
  "ts": "2026-05-22T18:30:00+0200",
  "tariff": "peak",
  "avg_p": 850.5,
  "period_wh": 14.175,
  "today_peak_wh": 4253.7,
  "today_off_peak_wh": 1820.4,
  "life_peak_wh": 285431.2,
  "life_off_peak_wh": 178654.9
}

Sample daily roll-over payload (rbamp/tou/day_close):

json

{"yday":141,"peak_wh":4253.7,"off_peak_wh":1820.4,"total_wh":6074.1}

Example comparison

#	Complexity	Display	MQTT	DRDY	Multi-module	Bidirectional	Persistence	Use case
1	minimal	Serial	—	—	—	—	—	smoke test
2	low	OLED	—	—	—	—	RAM	boxed meter
3	low	Serial	—	—	yes (3)	—	—	home monitoring
4	medium	—	yes	—	—	—	RAM	per-appliance in HA
5	medium	Serial	—	yes	—	yes (master-side)	RAM	solar home on BASIC tier
6	high	—	yes	—	yes (3)	yes	RAM	full home balance
7	medium	Serial + SD	—	yes	—	—	SD card	event detection
8	medium	—	yes (+disco)	—	—	optional	RAM + MQTT	HA auto-discovery integration
9	medium	—	yes	—	—	—	RTC memory	off-grid / outdoor logger
10	medium	Serial	yes	—	—	optional	RAM + MQTT (day close)	TOU peak/off-peak metering with NTP wall-clock

Best practices

Always check DATA_VALID after boot and PERIOD_VALID after CMD_LATCH_PERIOD.
Use delay(50) after a latch before reading the snapshot.
The master clock is authoritative for Wh — do not use PERIOD_LATCH_MS from the chip.
DRDY helps at high polling rates (≥ 5 Hz); ordinary polling is fine at low rates (≤ 1 Hz).
For multi-module setups, broadcast latch via general call delivers precise synchronisation (firmware 1.0+).
Master-side persistence is mandatory for long-term accounting — rbAmp does not store Wh, only the current avg_P.
When swapping an rbAmp in a running system, save the accumulated total_wh master-side before the swap and restore it afterwards — the new module starts its counters from zero.

What next

Once you are comfortable with these ten examples, build the integration code for your target platform. Pre-built libraries:

Arduino → RbAmp class (see 17_arduino_library.md)
ESPHome → external component (full deep-dive at tools/esphome-rbamp/docs/en/)
MicroPython → rbamp package (see 18_micropython_library.md)
ESP-IDF → rbamp component (see 19_esp_idf_library.md)
Linux SBC (CPython) → rbamp package (see 20_python_sbc_library.md)
Tasmota → Berry driver — deferred (no library shipped)

If your platform is not covered, the Arduino examples here serve as a reference: port the rb_read_* helpers to your platform's I2C API and the rest of the logic stays the same.