• MCU: ESP32-S3-WROOM-1-N16R8
• Framework: Arduino for ESP32
• Build system: PlatformIO
• USB programming: Native ESP32-S3 USB Serial/JTAG on IO19/IO20, plus UART0 header J3.

Ini
[env:esp32-s3-devkitc-1]
platform = espressif32
board = esp32-s3-devkitc-1
framework = arduino
monitor_speed = 115200
upload_speed = 921600
build_flags =
  -D ARDUINO_USB_MODE=1
  -D ARDUINO_USB_CDC_ON_BOOT=1

Cpp
#include <Arduino.h>
#include <WiFi.h>

// ---------------- Pin definitions from schematic ----------------
#define FLOW_PULSE_PIN        4   // U1 IO4 -> R10 -> J2 pin 3, with 100k pulldown
#define SENSOR_UART_TX_PIN   17   // U1 IO17 -> J2 pin 4
#define SENSOR_UART_RX_PIN   18   // U1 IO18 -> J2 pin 5
#define SENSOR_AUX_GPIO_PIN   5   // U1 IO5 -> J2 pin 6
#define LED_WIFI_PIN          6   // U1 IO6 -> R8 -> D3
#define LED_FLOW_PIN          7   // U1 IO7 -> R9 -> D4

// USB native serial uses IO19/IO20 internally on ESP32-S3.
// UART0 debug is also available on J3: TXD0/GPIO43 and RXD0/GPIO44.

// ---------------- User configuration ----------------
const char* WIFI_SSID = "YOUR_WIFI_SSID";
const char* WIFI_PASSWORD = "YOUR_WIFI_PASSWORD";
const char* HTTP_HOST = "192.168.1.100";   // Replace with your server
const uint16_t HTTP_PORT = 8080;

// Calibration: pulses per liter depends on the selected external ultrasonic sensor module.
// Replace this with the sensor manufacturer's K-factor after selecting the sensor.
volatile uint32_t flowPulseCount = 0;
const float PULSES_PER_LITER = 450.0f;  // placeholder calibration constant

unsigned long lastReportMs = 0;
uint32_t lastPulseSnapshot = 0;
float totalLiters = 0.0f;

HardwareSerial SensorSerial(1);

void IRAM_ATTR onFlowPulse() {
  flowPulseCount++;
}

void setWiFiLed(bool on) {
  digitalWrite(LED_WIFI_PIN, on ? HIGH : LOW);
}

void setFlowLed(bool on) {
  digitalWrite(LED_FLOW_PIN, on ? HIGH : LOW);
}

void connectWiFi() {
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  Serial.print("Connecting to WiFi");

  uint8_t tries = 0;
  while (WiFi.status() != WL_CONNECTED && tries < 30) {
    setWiFiLed((tries & 1) != 0);
    delay(250);
    Serial.print('.');
    tries++;
  }

  if (WiFi.status() == WL_CONNECTED) {
    setWiFiLed(true);
    Serial.printf("\nWiFi connected, IP=%s\n", WiFi.localIP().toString().c_str());
  } else {
    setWiFiLed(false);
    Serial.println("\nWiFi not connected; continuing offline.");
  }
}

void initSensorInterface() {
  pinMode(FLOW_PULSE_PIN, INPUT);  // external R6 provides pulldown
  attachInterrupt(digitalPinToInterrupt(FLOW_PULSE_PIN), onFlowPulse, RISING);

  pinMode(SENSOR_AUX_GPIO_PIN, OUTPUT);
  digitalWrite(SENSOR_AUX_GPIO_PIN, HIGH);  // available as sensor enable/config line

  SensorSerial.begin(9600, SERIAL_8N1, SENSOR_UART_RX_PIN, SENSOR_UART_TX_PIN);
  Serial.println("Sensor interface initialized: pulse input + optional UART.");
}

bool sendHttpReport(float flowLpm, float totalL) {
  if (WiFi.status() != WL_CONNECTED) return false;

  WiFiClient client;
  if (!client.connect(HTTP_HOST, HTTP_PORT)) {
    Serial.println("HTTP connect failed");
    return false;
  }

  String body = String("{\"flow_lpm\":") + String(flowLpm, 3) +
                String(",\"total_l\":") + String(totalL, 3) + String("}");

  client.printf("POST /flow HTTP/1.1\r\n");
  client.printf("Host: %s\r\n", HTTP_HOST);
  client.printf("Content-Type: application/json\r\n");
  client.printf("Content-Length: %u\r\n", body.length());
  client.printf("Connection: close\r\n\r\n");
  client.print(body);
  client.stop();
  return true;
}

void setup() {
  pinMode(LED_WIFI_PIN, OUTPUT);
  pinMode(LED_FLOW_PIN, OUTPUT);
  setWiFiLed(false);
  setFlowLed(false);

  Serial.begin(115200);
  delay(1000);
  Serial.println("ESP32-S3 ultrasonic water flow meter starting...");

  initSensorInterface();
  connectWiFi();
}

void loop() {
  const unsigned long now = millis();

  if (WiFi.status() != WL_CONNECTED) {
    setWiFiLed(false);
    connectWiFi();
  }

  if (now - lastReportMs >= 1000) {
    noInterrupts();
    uint32_t pulseSnapshot = flowPulseCount;
    interrupts();

    uint32_t deltaPulses = pulseSnapshot - lastPulseSnapshot;
    lastPulseSnapshot = pulseSnapshot;

    float litersThisSecond = deltaPulses / PULSES_PER_LITER;
    totalLiters += litersThisSecond;
    float flowLpm = litersThisSecond * 60.0f;

    setFlowLed(deltaPulses > 0);
    Serial.printf("Pulses=%lu, Flow=%.3f L/min, Total=%.3f L\n",
                  (unsigned long)deltaPulses, flowLpm, totalLiters);

    sendHttpReport(flowLpm, totalLiters);
    lastReportMs = now;
  }
}

Bash
pio run
pio run -t upload
pio device monitor -b 115200