ESP32 Soil Moisture Monitor

/*
 * ESP32 Soil Moisture Monitor — Advanced
 * ThingSpeak logging + Pushover notifications + MQTT
 * Libraries: Adafruit_SSD1306, PubSubClient, HTTPClient (built-in)
 */
#include <WiFi.h>
#include <HTTPClient.h>
#include <PubSubClient.h>

const char* SSID     = "YOUR_WIFI_SSID";
const char* PASSWORD = "YOUR_WIFI_PASSWORD";
const char* BROKER   = "192.168.1.100";

// ThingSpeak
const char* TS_API_KEY = "YOUR_THINGSPEAK_WRITE_KEY";
const char* TS_URL     = "https://api.thingspeak.com/update";

// Pushover (push notifications to phone)
const char* PO_TOKEN   = "YOUR_PUSHOVER_APP_TOKEN";
const char* PO_USER    = "YOUR_PUSHOVER_USER_KEY";
const char* PO_URL     = "https://api.pushover.net/1/messages.json";

#define MUX_SIG  34
#define MUX_S0   25
#define MUX_S1   26
#define MUX_S2   27
#define PUMP_PIN 32
#define ZONES    4
#define DRY_PCT  25     // Critical threshold for push notification
#define AIR_VALUE   2800
#define WATER_VALUE 1200

WiFiClient net;
PubSubClient mqtt(net);
int lastNotifiedZone = -1;

int readChannel(int ch){
  digitalWrite(MUX_S0,(ch>>0)&1);
  digitalWrite(MUX_S1,(ch>>1)&1);
  digitalWrite(MUX_S2,(ch>>2)&1);
  delay(10);
  long s=0; for(int i=0;i<10;i++){s+=analogRead(MUX_SIG);delay(3);}
  return constrain(map((int)(s/10),AIR_VALUE,WATER_VALUE,0,100),0,100);
}

void uploadThingSpeak(int* pct){
  HTTPClient http;
  String url=String(TS_URL)+"?api_key="+TS_API_KEY;
  for(int i=0;i<ZONES;i++) url+="&field"+String(i+1)+"="+String(pct[i]);
  http.begin(url); http.GET(); http.end();
  Serial.println("ThingSpeak updated");
}

void sendPushover(int zone, int pct){
  HTTPClient http;
  http.begin(PO_URL);
  http.addHeader("Content-Type","application/x-www-form-urlencoded");
  String body="token="+String(PO_TOKEN)+"&user="+String(PO_USER)
    +"&title=Plant+Alert&message=Zone+"+String(zone+1)+"+is+at+"+String(pct)+"%25+moisture+-+water+now!";
  http.POST(body); http.end();
  Serial.printf("Pushover alert sent for zone %dn",zone+1);
}

void publishMQTT(int* pct){
  if(!mqtt.connected()) return;
  for(int i=0;i<ZONES;i++){
    String topic="esp32engine/soil/zone"+String(i+1);
    mqtt.publish(topic.c_str(),String(pct[i]).c_str(),true);
  }
}

void setup(){
  Serial.begin(115200);
  analogReadResolution(12);
  pinMode(MUX_S0,OUTPUT);pinMode(MUX_S1,OUTPUT);pinMode(MUX_S2,OUTPUT);
  pinMode(PUMP_PIN,OUTPUT);digitalWrite(PUMP_PIN,LOW);
  WiFi.begin(SSID,PASSWORD);
  while(WiFi.status()!=WL_CONNECTED) delay(400);
  mqtt.setServer(BROKER,1883);
  mqtt.connect("soil-monitor");
}

void loop(){
  if(!mqtt.connected()) mqtt.connect("soil-monitor");
  mqtt.loop();

  int pct[ZONES];
  for(int z=0;z<ZONES;z++) pct[z]=readChannel(z);

  publishMQTT(pct);

  for(int z=0;z<ZONES;z++){
    if(pct[z]<DRY_PCT && lastNotifiedZone!=z){
      sendPushover(z,pct[z]);
      lastNotifiedZone=z;
      // Auto-water
      digitalWrite(PUMP_PIN,HIGH); delay(5000); digitalWrite(PUMP_PIN,LOW);
    }
    if(pct[z]>=40) lastNotifiedZone=-1; // Reset after plant is watered
  }

  uploadThingSpeak(pct);
  delay(900000); // 15 minute upload interval (ThingSpeak free: 15s min)
}