1. Executive Summary & Architecture

The Smart Water Meter Pulse Counter is a non-invasive retrofittable monitoring module engineered for residential and commercial municipal water meters. Built on the energy-efficient RISC-V ESP32-C3 microcontroller, the device utilizes an LJ12A3-4-Z/BX inductive proximity sensor (or Hall effect sensor) affixed directly to the glass face of mechanical rotating-disc water meters. As the internal metallic target rotates once per liter, the sensor triggers clean digital pulse transitions.

The firmware executes continuous pulse accumulation, volumetric flow rate computation (L/min), and automated leak detection algorithms (continuous flow exceeding 60 minutes). Telemetry is published securely over Wi-Fi MQTT with TLS directly to Home Assistant, alongside an integrated local web server and captive portal.

+--------------------------------------------------------------+
|                    ESP32-C3 Water Sentry                     |
|                                                              |
|  +---------------------+        +-------------------------+  |
|  | LJ12A3-4-Z/BX Metal | -----> | Hardware Debounced      |  |
|  | Proximity Sensor    |        | Edge Interrupt Counter  |  |
|  +---------------------+        +-------------------------+  |
|                                              |               |
|                                              v               |
|  +--------------------------------------------------------+  |
|  | Non-Volatile Flash (NVS) Cumulative Liter Storage      |  |
|  +--------------------------------------------------------+  |
|             |                                |               |
|             v                                v               |
|  +---------------------+        +-------------------------+  |
|  | MQTT TLS Home       |        | Continuous Leak & Burst |  |
|  | Assistant Publisher |        | Flow Alarm Engine       |  |
|  +---------------------+        +-------------------------+  |
+--------------------------------------------------------------+

2. Mathematical Modeling & Hydrodynamics

2.1 Volumetric Discharge & Pulse Integration

Each mechanical meter disc rotation represents a discrete volume \Delta V = 1.0 \text{ Liter} (or 0.1 \text{ L} depending on dial gear ratio). Cumulative consumption V_{total} across N pulses:

Instantaneous flow rate Q(t) in Liters per minute is computed using pulse period \Delta t_k = t_k - t_{k-1} (in seconds):

2.2 Leak Detection Heuristic State Machine

A persistent low-volume leak (dripping tap, running toilet flapper) is identified when:

If positive flow persists continuously for 1 hour without a single 15-minute zero-flow window, a critical leak notification is dispatched.

3. Bill of Materials (Dual Currency INR / USD)

4. FreeRTOS Task Architecture

1. 1.
   `pulse_isr` (Hardware Interrupt): Executes on FALLING edge of optocoupled proximity signal, incrementing 64-bit RAM counter and measuring interval with microsecond precision.
2. 2.
   `nvs_sync_task` (Priority 2): Flushes accumulated liter totals to ESP32 Non-Volatile Storage (NVS) every 10 liters or once per hour to guarantee resilience across power failures.
3. 3.
   `mqtt_report_task` (Priority 3): Publishes JSON state payload ({"liters_total": 14205, "flow_rate_lpm": 4.2, "leak_status": "NORMAL"}) to Home Assistant over Wi-Fi.

5. Frequently Asked Questions (Search Intent & Troubleshooting)

Why is an optocoupler required between the LJ12A3-4 sensor and ESP32?

The LJ12A3-4-Z/BX inductive sensor requires 6V–36V DC to operate reliably (typically 12V). Connecting its NPN open-collector output directly to an ESP32 GPIO can damage the 3.3V microcontroller if pullups are referenced to 12V. A PC817 optocoupler provides complete electrical isolation.

How does the counter avoid false counts from pipe vibrations?

The firmware implements an interrupt lockout window (T_{lockout} = 80 \text{ ms}), corresponding to a maximum physical flow rate of 12.5 L/sec (750 L/min), safely filtering out high-frequency mechanical contact flutter or water hammer shockwaves.

Pinout & Wiring Specifications

Pinout and Wiring Guide: Smart Water Meter Pulse Counter

1. Pin Assignment Table

2. LJ12A3-4-Z/BX Proximity Sensor & PC817 Optocoupler Interface

• LJ12A3 Brown Wire (+): Connect to +12V DC power rail.
• LJ12A3 Blue Wire (-): Connect to 12V DC power supply Ground.
• LJ12A3 Black Wire (Signal): Connect to PC817 Optocoupler Input Cathode (Pin 2).
• PC817 Anode (Pin 1): Connect to +12V DC through a 1.2kΩ 0.5W current-limiting resistor.
• PC817 Collector (Pin 4): Connect to ESP32-C3 GPIO4 with a 10kΩ pullup to 3.3V.
• PC817 Emitter (Pin 3): Connect to ESP32-C3 GND.

3. Circuit Schematic (ASCII)

[+12V DC Supply]
|
+----+------------------------> [LJ12A3 Sensor Brown Wire (+)]
|    |
|    +--[ 1.2k Resistor ]-----> [PC817 Pin 1: Anode]
|
|    [LJ12A3 Black Wire]-----> [PC817 Pin 2: Cathode]
|
+-----------------------------> [LJ12A3 Sensor Blue Wire (-)]
|
v (12V GND)
[Isolated Logic Domain]
[ESP32-C3 Controller]                              [PC817 Optocoupler Output]
+--------------------+                            +--------------------------+
|              GPIO4 |<---------------------------| Pin 4: Collector         |
|                    |       [ 10k Resistor ]     |                          |
|               3.3V |--------------+             |                          |
|                GND |----------------------------| Pin 3: Emitter           |
+--------------------+                            +--------------------------+

Arduino C++ Firmware Source Code

/*
* Smart Water Meter Pulse Counter with Inductive Proximity Sensor
* Target: ESP32-C3 + LJ12A3-4-Z/BX Inductive Sensor + Optocoupler
*/
#include <Arduino.h>
#include <WiFi.h>
#define PULSE_PIN       4  // Connected to PC817 optocoupler collector
#define STATUS_LED      8
volatile uint32_t pulse_count = 0;
volatile unsigned long last_pulse_time = 0;
static const unsigned long DEBOUNCE_MS = 80;
void IRAM_ATTR pulse_isr() {
unsigned long now = millis();
if (now - last_pulse_time > DEBOUNCE_MS) {
pulse_count++;
last_pulse_time = now;
}
}
void setup() {
Serial.begin(115200);
pinMode(STATUS_LED, OUTPUT);
digitalWrite(STATUS_LED, LOW);
pinMode(PULSE_PIN, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(PULSE_PIN), pulse_isr, FALLING);
Serial.println("Smart Water Meter Pulse Counter Initialized.");
}
void loop() {
static unsigned long last_report = 0;
static uint32_t last_count = 0;
if (millis() - last_report >= 5000) {
last_report = millis();
uint32_t delta = pulse_count - last_count;
last_count = pulse_count;
// 1 pulse = 1 liter
float flow_lpm = ((float)delta / 5.0f) * 60.0f; // Liters per minute
Serial.printf("[Water Meter] Total Consumption: %u Liters | Flow Rate: %.2f L/min
",
pulse_count, flow_lpm);
}
vTaskDelay(pdMS_TO_TICKS(100));
}