• MCU/module: ESP32-S3-WROOM-1-N16R8
• Framework: Arduino on PlatformIO
• Sensor interface: RS485 Modbus RTU over UART
• USB: ESP32-S3 native USB on IO19/IO20 for programming/debug if configured by board support package

Ini
[env:esp32-s3-devkitc-1]
platform = espressif32
board = esp32-s3-devkitc-1
framework = arduino
monitor_speed = 115200
upload_speed = 921600
lib_deps =
    4-20ma/ModbusMaster@^2.0.1

Cpp
#include <Arduino.h>
#include <WiFi.h>
#include <HTTPClient.h>
#include <ModbusMaster.h>
#include <string.h>

// Pin definitions from schematic
#define RS485_TX_PIN       17
#define RS485_RX_PIN       18
#define RS485_DE_RE_PIN    16
#define SENSOR_12V_EN_PIN  15
#define LED_WIFI_PIN        4
#define LED_FLOW_PIN        5

// Configuration placeholders
static const char* WIFI_SSID = "YOUR_SSID";
static const char* WIFI_PASSWORD = "YOUR_PASSWORD";
static const char* POST_URL = "http://192.168.1.100:8080/flow";

#define MODBUS_BAUD             9600
#define MODBUS_SLAVE_ADDR       1
#define SENSOR_READ_INTERVAL_MS 1000

// Example Modbus register assumptions. Update these to the actual sensor manual.
#define REG_FLOW_RATE_START     0x0000  // assumed float32, L/min, 2 holding registers
#define REG_TOTAL_VOLUME_START  0x0002  // assumed float32, L, 2 holding registers

ModbusMaster modbus;
unsigned long lastSensorReadMs = 0;

void rs485PreTransmission() {
  digitalWrite(RS485_DE_RE_PIN, HIGH);
  delayMicroseconds(50);
}

void rs485PostTransmission() {
  delayMicroseconds(50);
  digitalWrite(RS485_DE_RE_PIN, LOW);
}

float registersToFloat(uint16_t hi, uint16_t lo) {
  uint32_t raw = ((uint32_t)hi << 16) | lo;
  float value;
  memcpy(&value, &raw, sizeof(value));
  return value;
}

bool readFloat32Holding(uint16_t startReg, float& value) {
  uint8_t result = modbus.readHoldingRegisters(startReg, 2);
  if (result != modbus.ku8MBSuccess) {
    Serial.printf("Modbus read failed at 0x%04X: 0x%02X\n", startReg, result);
    return false;
  }
  value = registersToFloat(modbus.getResponseBuffer(0), modbus.getResponseBuffer(1));
  return true;
}

void initWiFi() {
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);

  Serial.print("Connecting to WiFi");
  for (int i = 0; i < 30 && WiFi.status() != WL_CONNECTED; ++i) {
    digitalWrite(LED_WIFI_PIN, !digitalRead(LED_WIFI_PIN));
    delay(500);
    Serial.print('.');
  }

  if (WiFi.status() == WL_CONNECTED) {
    digitalWrite(LED_WIFI_PIN, HIGH);
    Serial.printf("\nWiFi connected, IP: %s\n", WiFi.localIP().toString().c_str());
  } else {
    digitalWrite(LED_WIFI_PIN, LOW);
    Serial.println("\nWiFi not connected; continuing offline.");
  }
}

void postFlowReading(float flowLpm, float totalLiters) {
  if (WiFi.status() != WL_CONNECTED) return;

  HTTPClient http;
  http.begin(POST_URL);
  http.addHeader("Content-Type", "application/json");

  String payload = "{\"flow_lpm\":" + String(flowLpm, 3) +
                   ",\"total_liters\":" + String(totalLiters, 3) + "}";
  int code = http.POST(payload);
  Serial.printf("HTTP POST %d: %s\n", code, payload.c_str());
  http.end();
}

void setup() {
  Serial.begin(115200);
  delay(250);
  Serial.println("ESP32-S3 WiFi Water Flow Meter starting...");

  pinMode(LED_WIFI_PIN, OUTPUT);
  pinMode(LED_FLOW_PIN, OUTPUT);
  pinMode(SENSOR_12V_EN_PIN, OUTPUT);
  pinMode(RS485_DE_RE_PIN, OUTPUT);

  digitalWrite(LED_WIFI_PIN, LOW);
  digitalWrite(LED_FLOW_PIN, LOW);
  digitalWrite(RS485_DE_RE_PIN, LOW);     // receive by default
  digitalWrite(SENSOR_12V_EN_PIN, HIGH);  // enable 12V sensor rail

  Serial2.begin(MODBUS_BAUD, SERIAL_8N1, RS485_RX_PIN, RS485_TX_PIN);
  modbus.begin(MODBUS_SLAVE_ADDR, Serial2);
  modbus.preTransmission(rs485PreTransmission);
  modbus.postTransmission(rs485PostTransmission);

  initWiFi();
  Serial.println("Initialization complete.");
}

void loop() {
  if (WiFi.status() != WL_CONNECTED) {
    digitalWrite(LED_WIFI_PIN, LOW);
    static unsigned long lastReconnect = 0;
    if (millis() - lastReconnect > 10000) {
      lastReconnect = millis();
      initWiFi();
    }
  }

  if (millis() - lastSensorReadMs >= SENSOR_READ_INTERVAL_MS) {
    lastSensorReadMs = millis();

    float flowLpm = 0.0f;
    float totalLiters = 0.0f;
    bool okFlow = readFloat32Holding(REG_FLOW_RATE_START, flowLpm);
    bool okTotal = readFloat32Holding(REG_TOTAL_VOLUME_START, totalLiters);

    if (okFlow) {
      digitalWrite(LED_FLOW_PIN, flowLpm > 0.01f ? HIGH : LOW);
      Serial.printf("Flow: %.3f L/min", flowLpm);
      if (okTotal) Serial.printf(", Total: %.3f L", totalLiters);
      Serial.println();
      if (okTotal) postFlowReading(flowLpm, totalLiters);
    } else {
      digitalWrite(LED_FLOW_PIN, LOW);
    }
  }
}

Bash
pio run
pio run -t upload
pio device monitor