7 in 1 Soil Sensor (N, P, K, pH, EC, Moisture, Temperature), RS485, 5–30V

// NPKPHCTH-S - 9-parameter soil sensor | ESP32 + ThingSpeak

// RS485 module connected to Serial1 (RX=17, TX=16), RE/DE pin=4

// Baud rate: 4800, 8N1, sensor default address: 0x01

// Data is uploaded to ThingSpeak every 10 minutes

#include "WiFi.h"

#include "ThingSpeak.h"

#define RE    4

#define RXD2 17

#define TXD2 16

const char* ssid     = "YOUR_SSID";

const char* password = "YOUR_PASSWORD";

unsigned long channelID  = 0;           // your ThingSpeak channel ID

const char*   writeAPIKey = "YOUR_KEY"; // your ThingSpeak write API key

WiFiClient client;

// Modbus RTU requests - one register each (address 0x01, function 0x03)

const byte humi[]  = {0x01, 0x03, 0x00, 0x00, 0x00, 0x01, 0x84, 0x0A};

const byte temp[]  = {0x01, 0x03, 0x00, 0x01, 0x00, 0x01, 0xD5, 0xCA};

const byte cond[]  = {0x01, 0x03, 0x00, 0x02, 0x00, 0x01, 0x25, 0xCA};

const byte phph[]  = {0x01, 0x03, 0x00, 0x03, 0x00, 0x01, 0x74, 0x0A};

const byte nitro[] = {0x01, 0x03, 0x00, 0x04, 0x00, 0x01, 0xC5, 0xCB};

const byte phos[]  = {0x01, 0x03, 0x00, 0x05, 0x00, 0x01, 0x94, 0x0B};

const byte pota[]  = {0x01, 0x03, 0x00, 0x06, 0x00, 0x01, 0x64, 0x0B};

const byte sali[]  = {0x01, 0x03, 0x00, 0x07, 0x00, 0x01, 0x35, 0xCB};

const byte tds[]   = {0x01, 0x03, 0x00, 0x08, 0x00, 0x01, 0x05, 0xC8};

byte values[7];

int readRegister(const byte* request, uint8_t len) {

  digitalWrite(RE, HIGH);

  delay(10);

  for (uint8_t i = 0; i < len; i++) Serial1.write(request[i]);

  Serial1.flush();

  digitalWrite(RE, LOW);

  delay(100);

  unsigned long t = millis();

  uint8_t idx = 0;

  while (millis() - t < 300 && idx < 7) {

    if (Serial1.available()) values[idx++] = Serial1.read();

  }

  if (idx < 5) return -1;

  return int(values[3] << 8 | values[4]);

}

void setup() {

  Serial.begin(115200);

  Serial1.begin(4800, SERIAL_8N1, RXD2, TXD2);

  pinMode(RE, OUTPUT);

  digitalWrite(RE, LOW);

  delay(1000);

  WiFi.mode(WIFI_STA);

  ThingSpeak.begin(client);

  Serial.println("NPKPHCTH-S ready.");

}

void loop() {

  if (WiFi.status() != WL_CONNECTED) {

    Serial.print("Connecting to WiFi...");

    while (WiFi.status() != WL_CONNECTED) {

      WiFi.begin(ssid, password);

      delay(5000);

    }

    Serial.println(" connected.");

  }

  int raw;

  float val[9];

  const byte* reqs[]   = {humi, temp, cond, phph, nitro, phos, pota, sali, tds};

  uint8_t     lens[]   = {sizeof(humi), sizeof(temp), sizeof(cond), sizeof(phph),

                           sizeof(nitro), sizeof(phos), sizeof(pota),

                           sizeof(sali), sizeof(tds)};

  float       scales[] = {10.0, 10.0, 1.0, 10.0, 1.0, 1.0, 1.0, 1.0, 1.0};

  const char* names[]  = {"Humidity","Temperature","EC","pH",

                           "Nitrogen","Phosphorus","Potassium","Salinity","TDS"};

  const char* units[]  = {"%","deg.C","uS/cm","","mg/kg",

                           "mg/kg","mg/kg","g/L","mg/L"};

  for (uint8_t i = 0; i < 9; i++) {

    raw = readRegister(reqs[i], lens[i]);

    val[i] = (raw >= 0) ? raw / scales[i] : -1;

    Serial.print(names[i]); Serial.print(": ");

    if (raw >= 0) { Serial.print(val[i], (scales[i] > 1) ? 1 : 0);

                    Serial.println(units[i]); }

    else Serial.println("read error");

    delay(200);

  }

  // Upload to ThingSpeak (8 fields max per free channel)

  ThingSpeak.setField(1, val[0]); // humidity

  ThingSpeak.setField(2, val[1]); // temperature

  ThingSpeak.setField(3, val[2]); // EC

  ThingSpeak.setField(4, val[3]); // pH

  ThingSpeak.setField(5, val[4]); // nitrogen

  ThingSpeak.setField(6, val[5]); // phosphorus

  ThingSpeak.setField(7, val[6]); // potassium

  ThingSpeak.setField(8, WiFi.RSSI());

  int status = ThingSpeak.writeFields(channelID, writeAPIKey);

  Serial.println(status == 200 ? "Upload OK." :

                 "Upload failed, HTTP " + String(status));

  Serial.println("----------------------------------");

  delay(600000); // 10 minutes

}