Basic idea was to build a simple, cheap temperature sensing circuit-manually calibrated. then display the temperature in real-time on an 8x8 LED matrix.

1. Arduino Final Project
By: Mhmoud Salama.
Hussam Hamdy.

2. Main Project
• To make a temperature sensor that outputs the reading
as a scrolling message on a LED matrix.
• We used a LED matrix which is a common anode 8x8
display.
• Wired on breadboards.

3. Main Concept
• Use of two shift registers (2x 74HC595) to pass the
encoded-charachter data serially from the arduino as a
parallel output to the rows and Columns of an 8x8 LED
matrix.
• The arduino handles the scrolling of the message and the
periodic time-multiplexing of rows and columns (refresh
rate = 100Hz), using a periodic interrupt, to which the
function “screenUpdate” is attached.
• So , we calibrated the sensor using a potentiometer
through the serial monitor window.
• then the complete circuit is connected.

4. Wiring Diagram

5. 74HC595-Shift Registers
-- An 8-bit shift register with
Serial to parallel capability.
-- We use two of them, Each
one controlling eight
rows/columns.

6. LM335-Temperature Sensor
• Calibration:
-- We connect the calibration circuit , and
connected it’s output as an analogue input to
the arduino.
-- With a potentiometer, and a small code...
we used the serial monitor of arduino to
fine-tune the sensor to give an acceptable
reading (28 C for average room temperature).

7. CODE
• #include <TimerOne.h>
• #include <charEncodings.h> // Each charachter and it’s (8x8 LED matrix)-mapped code.
• // BASIC PIN CONFIGURATION
• // AND DECLARATIONS
• //Pin connected to Pin 12 of 74HC595 (Latch)
• int latchPin = 8;
• //Pin connected to Pin 11 of 74HC595 (Clock)
• int clockPin = 12;
• //Pin connected to Pin 14 of 74HC595 (Data)
• int dataPin = 11;
• // pin for the potentiometer to control the scrolling speed
• int potPin = 5;
• // pin for reading the temperature
• int tempPin = 4;
• // this is the gobal array that represents what the matrix
• // is currently displaying
• uint8_t led[8];

8. CODE
• void setup()
• {
//set pins to output
• pinMode(latchPin, OUTPUT);
• pinMode(clockPin, OUTPUT);
• pinMode(dataPin, OUTPUT);
• pinMode(potPin, INPUT);
• pinMode(tempPin, INPUT);
• analogReference(INTERNAL);
• // attach the screenUpdate function to the interrupt timer
• // Period=10,000micro-second /refresh rate =100Hz
• Timer1.initialize(10000);
• Timer1.attachInterrupt(screenUpdate);
• }

9. CODE
• //Continuous LOOP
• void loop()
• {
• long counter1 = 0;
• long counter2 = 0;
• char reading[10];
• char buffer[18];
• if (counter1++ >=100000) {
• counter2++;
• }
• if (counter2 >= 10000) {
• counter1 = 0;
• counter2 = 0;
• }
getTemp(reading);
displayScrolledText(reading);
}

10. The (displayScrolledText ) Function
• void displayScrolledText(char* textToDisplay)
• {
• int textLen = strlen(textToDisplay);
• char charLeft, charRight;
• // scan through entire string one column at a time and call
• // function to display 8 columns to the right
• for (int col = 1; col <= textLen*8; col++)
• {
•
• // if (col-1) is exact multiple of 8 then only one character
• // involved, so just display that one
• if ((col-1) % 8 == 0 )
• {
• char charToDisplay = textToDisplay[(col-1)/8];
•
• for (int j=0; j<8; j++)
• {
• led[j] = charBitmaps[charToDisplay][j];
• }
• }
• else
• {
• int charLeftIndex = (col-1)/8;
• int charRightIndex = (col-1)/8+1;
• charLeft = textToDisplay[charLeftIndex];

11. • // check we are not off the end of the string
• if (charRightIndex <= textLen)
• {
• charRight = textToDisplay[charRightIndex];
• }
• else
• {
• charRight = ' ';
• }
• setMatrixFromPosition(charLeft, charRight, (col-1) % 8);
• }
• int delayTime = analogRead(potPin);
• delay (delayTime);
• }
•}

12. • void shiftIt(byte dataOut) {
• // Shift out 8 bits LSB first,
• // on rising edge of clock
• boolean pinState;
• //clear shift register read for sending data
• digitalWrite(dataPin, LOW);
• // for each bit in dataOut send out a bit
• for (int i=0; i<=7; i++) {
• //set clockPin to LOW prior to sending bit
• digitalWrite(clockPin, LOW);
• // if the value of DataOut and (logical AND) a bitmask
• // are true, set pinState to 1 (HIGH)
• if ( dataOut & (1<<i) ) {
• pinState = HIGH;
• }
• else {
• pinState = LOW;
• }
• //sets dataPin to HIGH or LOW depending on pinState
• digitalWrite(dataPin, pinState);
• //send bit out on rising edge of clock
• digitalWrite(clockPin, HIGH);
• digitalWrite(dataPin, LOW);
• }

13. • //stop shifting
• digitalWrite(clockPin, LOW);
• }
• boolean isKeyboardInput() {
• // returns true is there is any characters in the keyboard buffer
• return (Serial.available() > 0);
• }
• }
• // terminate the string
• readString[index] = '0';
• }

14. • void setMatrixFromPosition(char charLeft, char charRight, int col) {
• // take col left most columns from left character and bitwise OR with 8-col from
• // the right character
• for (int j=0; j<8; j++) {
• led[j] = charBitmaps[charLeft][j] << col | charBitmaps[charRight][j] >> 8-col;
• }
• }
• void screenUpdate() {
• uint8_t col = B00000001;
• for (byte k = 0; k < 8; k++) {
• digitalWrite(latchPin, LOW); // Open up the latch ready to receive data
• shiftIt(~led[7-k]);
• shiftIt(col);
• digitalWrite(latchPin, HIGH); // Close the latch, sending the registers data to the matrix
• col = col << 1;
• }
• digitalWrite(latchPin, LOW);
• shiftIt(~0 );
• shiftIt(255);
• digitalWrite(latchPin, HIGH);
• }

15. • void getTemp(char* reading) {
• int span = 20;
• int aRead = 0;
• long temp;
• char tmpStr[10];
• // average out several readings
• for (int i = 0; i < span; i++) {
• aRead = aRead+analogRead(tempPin);
• }
• aRead = aRead / span;
• temp = ((100*1.1*aRead)/1024)*10;
• reading[0] = '0';
• itoa(temp/10, tmpStr, 10);
• strcat(reading,tmpStr);
• strcat(reading, ".");
• itoa(temp % 10, tmpStr, 10);
• strcat(reading, tmpStr);
• strcat(reading, "C");
• }