An Arduino Thermometer with Digital Display

Step 4: Let’s Start by Reading the Temperature

We’ll start by reading the temperature from the TMP36 and sending the value to the Serial Monitor (Tools -> Serial Monitor on the Arduino IDE).

The TMP36 outputs a voltage on the SIG pin proportional to temperature.

Zero degrees Celcius = 500mV   (0.5)

Each degree above that = 10mV   (1/100)

Here’s a code segment:

float temperature = getVoltage(A0);                        // Get the voltage reading
temperature = (temperature – .5) * 100;                  // Convert to Temperature (degrees C)

/*
* setup() – this function runs once when you turn your Arduino on
* We initialize the serial connection with the computer
*/
void setup()
{
Serial.begin(9600);  //Start the serial connection with the computer
}

void loop()                     // run over and over again
{
float temperature = getVoltage(temperaturePin);  // Get the Voltage reading from the tem

perature sensor
temperature = (temperature – .5) * 100;                 // Convert from 10 mv per degree with 500mV offsetSerial.println(temperature);                     // Print the result
delay(1000);                                             // Wait a second
}

/*
* getVoltage() – returns the voltage on the analog input defined by
* pin
*/
float getVoltage(int pin){
return (analogRead(pin) * 5.0/1024); //converting from a 0 to 1023 digital range
// to 0 to 5 volts (each 1 reading equals ~ 5 mV)
}

and Draw the relevant digit in the Loop section:

Myfont::Draw(x_pos, ‘a’);                 // Send a character to the LOL shield

where x_pos is an int holding the x position where you want the number to be display (zero is the left hand edge).

In the final code you will need to convert the temperature reading (a float). To a char so that it can be displayed on the LOL shield using the Draw command.

To do this we use ltoa in C as follows:

temperature = (temperature – .5) * 100;        // Convert to Temperature (a float)

ltoa(long(temperature), buffer, 10);            // buffer is a 12 location char i.e. char buffer[12];
for (int i=0; i<2; i++) {                                   // Iterate through the buffer for 2 characters
   Myfont::Draw(1 + i*6,buffer[i]);                 // Send each character to the LOL shield
}

Notice the x position is:
1 + i*6
this means the first character (i=0) is at x position 1
and their spaced 6 apart (e.g. i=1, x position = 1 + 6 = 7

Also notice the buffer for ltoa() is 12 long. This is a detail related to the length of long in C and allocation of sufficient memory.