A quick course in Binary

project #20: creating a digital thermometer

In this project we’ll add the TMP36 temperature sensor we created in Chapter 4 to the double-digit circuit constructed for Project 19 to create a digital thermometer. The algorithm is simple: we read the voltage returned from the TMP36 (using the method from Project 12) and convert the reading to degrees Celsius.

The Hardware

The following hardware is required:

• 
  The double-digit circuit from Project 19
  
• 
  One TMP36 temperature sensor
  

Connect the center output lead of the TMP36 to analog pin 5, the left lead to 5 V, and the right lead to GND, and you’re ready to measure.

The Sketch

Here is the sketch:
// Project 20 - Creating a Digital Thermometer
#define DATA 6 // connect to pin 14 on the 74HC595
#define LATCH 8 // connect to pin 12 on the 74HC595 #define CLOCK 10 // connect to pin 11 on the 74HC595
int temp = 0; float voltage = 0; float celsius = 0; float sensor = 0; int digits[]={
252, 96, 218, 242, 102, 182, 190, 224, 254, 246, 238, 62, 156, 122, 158, 142};
void setup()
{
pinMode(LATCH, OUTPUT);
pinMode(CLOCK, OUTPUT); pinMode(DATA, OUTPUT);
}
void displayNumber(int n)
{
int left, right = 0; if (n < 10) {
digitalWrite(LATCH, LOW);
shiftOut(DATA, CLOCK, LSBFIRST, digits[n]); shiftOut(DATA, CLOCK, LSBFIRST, digits[0]); digitalWrite(LATCH, HIGH);
}
if (n >= 10)
{ right = n % 10; left = n / 10; digitalWrite(LATCH, LOW);
shiftOut(DATA, CLOCK, LSBFIRST, digits[right]); shiftOut(DATA, CLOCK, LSBFIRST, digits[left]); digitalWrite(LATCH, HIGH);
} }
void loop() {
sensor = analogRead(5);
voltage = (sensor * 5000) / 1024; // convert raw sensor value to millivolts voltage = voltage - 500; // remove voltage offset celsius = voltage / 10; // convert millivolts to Celsius temp = int(celsius); // change the floating point temperature to an int displayNumber(temp); delay(500);
}
The sketch is simple and borrows code from previous projects: displayNumber() from Project 19 and the temperature calculations from Project 12. The delay(500); function in the second-to-last line of the sketch keeps the display from changing too quickly when the temperature fluctuates.