Soil Moisture Monitor using ESP32

Reads a capacitive soil sensor and shows moisture percentage on the serial monitor. A simple first IoT project.

Block diagram

Components

Wiring

⚠ Power the sensor from 3V3, not 5V. Use ADC1 pins only — ADC2 stops working when Wi-Fi is on. Match pins by their printed label.

Code

const int SENSOR_PIN = 34;
const int DRY = 3200;   // reading in dry air — calibrate
const int WET = 1300;   // reading in water — calibrate

void setup() {
  Serial.begin(115200);
}

void loop() {
  int raw = analogRead(SENSOR_PIN);
  int pct = constrain(map(raw, DRY, WET, 0, 100), 0, 100);
  Serial.printf("Raw: %d  Moisture: %d%%\n", raw, pct);
  delay(1000);
}

Calibration

Note the raw value with the sensor in dry air and again in a glass of water. Put those numbers in DRY and WET.