Self-watering plant monitor

Install first: Adafruit SSD1306, Adafruit GFX Library

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// ---- Pins ----
const int SOIL_PIN  = 34;   // analog input
const int RELAY_PIN = 26;   // relay IN

// ---- Calibration (update after step 6) ----
const int DRY_READING = 3200;  // sensor in dry air
const int WET_READING = 1300;  // sensor in water
const int WATER_BELOW_PERCENT = 35;
const unsigned long PUMP_SECONDS = 4;
const unsigned long REST_MINUTES = 10; // wait before watering again

Adafruit_SSD1306 display(128, 64, &Wire, -1);
unsigned long lastWatered = 0;

int moisturePercent() {
  long total = 0;
  for (int i = 0; i < 10; i++) { total += analogRead(SOIL_PIN); delay(5); }
  int raw = total / 10;
  int pct = map(raw, DRY_READING, WET_READING, 0, 100);
  return constrain(pct, 0, 100);
}

void show(int pct, const char* status) {
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.print("Soil moisture");
  display.setTextSize(3);
  display.setCursor(0, 18);
  display.print(pct);
  display.print("%");
  display.setTextSize(1);
  display.setCursor(0, 54);
  display.print(status);
  display.display();
}

void setup() {
  Serial.begin(115200);
  pinMode(RELAY_PIN, OUTPUT);
  digitalWrite(RELAY_PIN, LOW);
  Wire.begin(21, 22);
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED not found - check SDA/SCL wiring");
  }
}

void loop() {
  int pct = moisturePercent();
  Serial.printf("Moisture: %d%%\n", pct);

  bool rested = millis() - lastWatered > REST_MINUTES * 60UL * 1000UL || lastWatered == 0;
  if (pct < WATER_BELOW_PERCENT && rested) {
    show(pct, "Watering...");
    digitalWrite(RELAY_PIN, HIGH);
    delay(PUMP_SECONDS * 1000);
    digitalWrite(RELAY_PIN, LOW);
    lastWatered = millis();
  } else {
    show(pct, pct < WATER_BELOW_PERCENT ? "Dry - resting pump" : "All good");
  }
  delay(3000);
}