Cheap Digital Thermostat Display

This is a cheap but effective temperature monitor which displays the current temperature indoors onto a screen. It uses a TMP36 chip which read the temperature and a 16x2 LCD to display it. Overall it only costs about $18, depending on where you supply these items.

For this project, my goal is to monitor the temperature of my room, so I know when to properly ventilate it, especially with a few computers running full-time in the background, along with the stinking hot summer weather. I normally, have a high heat tolerance and don't notice the gradual changes even if it's around 28 degrees, so this device gives me an objective perspective.

In the future, I plan on mounting the IC outdoors, so I can monitor the weather and figure out what appropriate clothing to wear, especially helpful in hot summer days and cold winter days!

Step 1: Bill of Materials (BoM)

• Arduino Uno - $7
• Temperature Sensor - TMP36 - $2
• 16x2 LCD Screen - $7
• Jumper Cables - $1
• Potentiometer - $1

Step 2: LCD Screen Hookup

Distribute power in parallel using the breadboard's longest rails.

• Red Rail: Connect 3.3V pin of the Arduino to this rail.
• Black Rail: Connect any GND pin of the Arduino to this rail.

Connect the LCD to power

• Black, white, and brown wires: Connect pin 1, 5, and 16 of the LCD screen to the blue rail on the breadboard
• Yellow wires: connect pin 2 and 15 of the LCD screen to the red rail on the breadboard

Connect the LCD signals to the Arduino

• Purple, White (x2), Grey wires: Connect pins 14, 13, 12, and 11 on the LCD to pins 2, 3, 4, and 5 on the Arduino, respectively.
• Blue and Green wires: Connect pins 4 and 6 on the LCD to pins 11 and 12 on the Arduino.

Step 3: Wiring the Temperature Sensor

Be careful about the polarity of the temperature sensor when plugging it in, because reversing it will cause ti to overheat and may burn you.

I find it easiest to hold it with the flat edge facing my right, then I know the order is ground, signal, then VCC, all in order from top to bottom.

• Green wire: This is the ground pin, connect it to GND on the Arduino.

• Orange middle wire: This is the signal pin, connect it to pin A0 on the Arduino

• Orange outer wire: This is the VCC pin, connect it to 3.3V on the Arduino.

Potentiometer hookup (from picture)

• Brown wire: Connect pin 3 on the LCD to the potentiometer's middle signal pin. Then connect the outer pins of this potentiometer to the power rail, in any order, there is no polarity requirements.

Step 4: Coding

// Load the LiquidCrystal library
#include  <LiquidCrystal.h>

<liquidcrystal.h>// Initialize the library with the pins we're using.
LiquidCrystal lcd(12,11,5,4,3,2);
//temperature analog input pin constant </liquidcrystal.h>

const int tempPin = 0;
//raw reading variable
int tempVal;
//voltage variable
float volts;
//final temperature variables
float tempC;
void setup()
{
  // begin lcd of this particular size
  lcd.begin(16, 2);
  // Data sent to the display will stay there until it's
  // overwritten or power is removed. 
  lcd.clear();
  // Now we'll display a message on the LCD!
  lcd.print("Current Temp:  ");
}  

void loop()
{
  //read the temp sensor and store it in tempVal
  tempVal = analogRead(tempPin);
  //converting that reading to voltage by multiplying the reading by 3.3V (voltage of       //the 101 board)
  volts = tempVal * 5.0;
  volts /= 1023.0;
  tempC = (volts - 0.5) * 100 ;
  lcd.setCursor(0,1);
  lcd.print(tempC);
  //wait a bit before taking another reading
  delay(1000);
}