An Arduino Thermometer With Digital Display

This is a project for Arduino to make a Thermometer with Digital Display, aimed at beginners.

Arduino measures the voltage on a TMP36 Temperature sensor, converts the Voltage to Degrees Celcius and Displays the value on an LOL shield display.

Objectives:
* Learn how to use the TMP36
* Learn how to perform numeric and string conversions in Arduino-C (sketch)
* Learn how to display numbers on the LOL shield

Step 1: What You Need

You will need:
* Arduino UNO
* LOL shield (http://jimmieprodgers.com/kits/lolshield/)
* TMP36 Temperature Sensing IC
* Breadboard for wiring up e.g. (http://www.oomlout.co.uk/prototyping-bundle-for-arduino-ardp-p-186.html)
* Some Wires

Step 2: Wire It Up

Wire the TMP36 as follows:
+5V
GND
SIG => A0

Note: The LOL shield does not come with Headers (as shown in the picture), attached to the topside.

I bought some here: http://www.amazon.co.uk/gp/product/B004RASBVY/ref=oh_details_o06_s00_i00

Step 3: Install the LOL Shield Libraries

Install the Arduino libraries for the LOL shield if you don't have them already.

You can get the link to them from this page:
http://jimmieprodgers.com/kits/lolshield/

Step 4: Let's Start by Reading the Temperature

The code for temperature reading is shown in the Next Step. Step 7 shows the full code for the project. For now let's see the main ideas that make the code work.

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)

Step 5: Here's the Full Code to Write Temperature to the Serial Monitor

/*
* Displays Temperature from TMP36 on the Serial Monitor
* Adapted from (and for more details on this circuit): http://tinyurl.com/c89tvd
*/

//TMP36 Pin Variables
int temperaturePin = 0; //the analog pin the TMP36's Vout (sense) pin is connected to
                        //the resolution is 10 mV / degree centigrade
                        //(500 mV offset) i.e. 0 degrees = 500mV

/*
* 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 temperature sensor
temperature = (temperature - .5) * 100;         // Convert from 10 mv per degree with 500mV offset

Serial.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)
}

Step 6: How to Use the Display

Once you've included the library:
#include "Myfont.h"

You need to initialise the display in the Setup section:
void setup()
{
    LedSign::Init();
}

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.

Step 7: Here's the Full Code

/*
* Displays Temperature from TMP36 numerically on an LOL shield
* Adapted from (and for more details on this circuit): http://tinyurl.com/c89tvd
*/
#include "Charliplexing.h"
#include "Myfont.h"

//TMP36 Pin Variables
int temperaturePin = 0; //the analog pin the TMP36's Vout (sense) pin is connected to
                        //the resolution is 10 mV / degree centigrade
                        //(500 mV offset) i.e. 0 degrees = 500mV

char buffer[12];

void setup()
{
    LedSign::Init();
    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 temperature sensor
temperature = (temperature - .5) * 100;                 // Convert to Temperature

Serial.println(temperature);                    // printing the result for debug
ltoa(long(temperature), buffer, 10);
for (int i=0; i<2; i++) {                                   // Iterate through the buffer
Myfont::Draw(1+i*6,buffer[i]);                         // Sending each character to the LOL shield
}
delay(1000);                                                     // wait a second
LedSign::Clear();                                  // Clear the display
}

/*
* 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)
}