Lesson 5 · Weeks 8-10

// PRP 5 — a single threshold decision.
//
// THRESHOLD is a design decision. Replace this value with one you
// chose from your own recorded readings, and be able to defend it.
//
// Expect this sketch to chatter when the reading sits near the
// threshold. That fault is the point of the activity — PRP 6 fixes it.

const int SENSOR_PIN = A0;
const int OUTPUT_PIN = 13;
const int THRESHOLD  = 500;   // <-- your number, from your data

void setup() {
  pinMode(OUTPUT_PIN, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int reading = analogRead(SENSOR_PIN);
  Serial.println(reading);

  if (reading < THRESHOLD) {
    digitalWrite(OUTPUT_PIN, HIGH);
  } else {
    digitalWrite(OUTPUT_PIN, LOW);
  }

  delay(100);
}

// PRP 6 — hysteresis.
//
// One threshold chatters because the sensor's own noise crosses it
// repeatedly. Two thresholds with a gap wider than that noise fixes it.
//
// Make the gap wider than the noise you measured in PRP 4, and no wider.

const int SENSOR_PIN = A0;
const int OUTPUT_PIN = 13;
const int TURN_ON_BELOW  = 480;   // <-- your numbers
const int TURN_OFF_ABOVE = 520;

bool outputOn = false;

void setup() {
  pinMode(OUTPUT_PIN, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int reading = analogRead(SENSOR_PIN);

  if (!outputOn && reading < TURN_ON_BELOW) {
    outputOn = true;
  } else if (outputOn && reading > TURN_OFF_ABOVE) {
    outputOn = false;
  }
  // Between the two thresholds nothing changes. That is the whole trick.

  digitalWrite(OUTPUT_PIN, outputOn ? HIGH : LOW);
  Serial.println(reading);
  delay(100);
}

// PRP 7 — automatic watering.
//
// Pump is driven through a motor driver module, NOT directly from a pin.
// A board pin supplies tens of milliamps; the pump wants hundreds.
//
// MAX_RUN_MS is the safety limit. If the sensor falls out of the soil or
// fails open, an unlimited pump empties the reservoir onto the bench.
// A control system that cannot fail safely is not finished.

const int MOISTURE_PIN = A0;
const int PUMP_PIN     = 9;      // to the driver module input

const int DRY_BELOW  = 400;      // <-- your calibrated numbers
const int WET_ABOVE  = 600;
const unsigned long MAX_RUN_MS  = 15000UL;   // never pump longer than this
const unsigned long REST_MS     = 60000UL;   // let water soak in before re-reading

bool pumping = false;
unsigned long pumpStartedAt = 0;
unsigned long pumpStoppedAt = 0;

void setup() {
  pinMode(PUMP_PIN, OUTPUT);
  digitalWrite(PUMP_PIN, LOW);
  Serial.begin(9600);
}

void loop() {
  int moisture = analogRead(MOISTURE_PIN);
  unsigned long now = millis();

  if (pumping) {
    bool wetEnough = moisture > WET_ABOVE;
    bool runTooLong = (now - pumpStartedAt) >= MAX_RUN_MS;

    if (wetEnough || runTooLong) {
      digitalWrite(PUMP_PIN, LOW);
      pumping = false;
      pumpStoppedAt = now;
      if (runTooLong) {
        Serial.println("STOPPED ON RUN LIMIT - check the sensor");
      }
    }
  } else {
    bool dry = moisture < DRY_BELOW;
    bool rested = (now - pumpStoppedAt) >= REST_MS;

    if (dry && rested) {
      digitalWrite(PUMP_PIN, HIGH);
      pumping = true;
      pumpStartedAt = now;
    }
  }

  Serial.println(moisture);
  delay(500);
}