Build an Educational Soil pH Monitor

// ESP32 educational soil pH monitor
// Uses a pH interface board on ADC1 GPIO34. Calibrate before reading soil slurry samples.
const int PH_PIN = 34;

const bool CALIBRATION_RECORDED = false; // Set true only after recording your own pH 7 and pH 4 ADC values.
const float PH7_ADC = 2048.0;            // Replace with stabilized ADC average in pH 7 buffer.
const float PH4_ADC = 1530.0;            // Replace with stabilized ADC average in pH 4 buffer.

float averageAdc() {
  long sum = 0;
  for (int i = 0; i < 30; i++) {
    sum += analogRead(PH_PIN);
    delay(20);
  }
  return sum / 30.0;
}

float estimatedPh(float raw) {
  float slope = (7.0 - 4.0) / (PH7_ADC - PH4_ADC);
  return 7.0 + slope * (raw - PH7_ADC);
}

void setup() {
  Serial.begin(115200);
  analogReadResolution(12);
  analogSetPinAttenuation(PH_PIN, ADC_11db);
  Serial.println("Educational soil pH monitor - calibrated estimates only.");
}

void loop() {
  if (!CALIBRATION_RECORDED) {
    Serial.println("Calibration required: record stable pH 7 and pH 4 buffer ADC values, update constants, then set CALIBRATION_RECORDED true.");
    delay(2000);
    return;
  }

  float raw = averageAdc();
  float voltage = raw * 3.3 / 4095.0;
  float ph = estimatedPh(raw);

  Serial.printf("Estimated calibrated pH: %.2f | ADC: %.0f | Interface voltage: %.2f V\n", ph, raw, voltage);
  delay(5000);
}