Project Eight - Thermostat

The final project in our series may seem complex, but is quite simple. We use the potentiometer to allow user input of a temperature value, and using the temperature sensor – if the ambient temperature rises above the value set via the potentiometer the relay is activated.

1. Connect the Temperature Sensor to the Analog A0/A1 input jack, like it was in Project 7.
2. The Grove produces an analog voltage on its D1 output, which is connected to Arduino A0 analog input on the A0/A1 input jack.
3. Connect the Potentiometer to the Analog A4/A5 input jack.
4. The Potentiometer produces an analog voltage on its D1 output, which is connected to Arduino A4 analog input on the A4/A5 input jack.
   Connect the Relay to the D2/D3 input jack.
5. The Arduino's D2 pin sends a signal to the Relay on the D1 connector. The Relay's red light indicates whether the relay is on or off, and the relay makes a clicking sound when it switches.
   

Now upload the following Arduino sketch:

// Project Eight - Thermostat
//

int a,c,d;
int z=3975; 
int relaypin=2;
float b, q, resistance, temperature; 

void setup()
{
  pinMode(relaypin, OUTPUT);
}

void loop()
{
  a=analogRead(4); 
  b=0.0488*a;
  c=int(b);
  q=analogRead(0);
  resistance=(float)(1023-q)*10000/q; 
  temperature=1/(log(resistance/10000)/z+1/298.15)-273.15; 
  d=int(temperature);
  if (d>=c)
  {
    digitalWrite(relaypin, HIGH);
    delay(500);
  } 
  if (d<c)
  {
    digitalWrite(relaypin, LOW);
    delay(500);
  }
}

Try turning the potentiometer to the right and left and see if the relay turns on or off.

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