Lesson 4 · Weeks 6-8

// PRP 3 — light sensing with an LDR.
// Wire the LDR and a fixed resistor as a divider, junction to A0.

const int LDR_PIN = A0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  int reading = analogRead(LDR_PIN);   // 0-1023, NOT a light level yet
  Serial.println(reading);
  delay(1000);
}

// PRP 4 — temperature and humidity, plotted over time.
// Requires the DHT sensor library.
//
// The DHT22 needs at least 2 seconds between reads. Sampling faster
// returns stale values or nan — it is the most common cause of both.

#include <DHT.h>

const int DHT_PIN = 2;
DHT dht(DHT_PIN, DHT22);

void setup() {
  Serial.begin(9600);
  dht.begin();
}

void loop() {
  float humidity = dht.readHumidity();
  float tempC = dht.readTemperature();

  if (isnan(humidity) || isnan(tempC)) {
    Serial.println("read failed");   // check wiring, and check you waited 2s
  } else {
    Serial.print(tempC);
    Serial.print(" ");
    Serial.println(humidity);       // two values, space separated, for the plotter
  }

  delay(2000);                       // minimum sampling interval for this sensor
}