How to Transmit Time and Temperature Using a TMP36 Sensor and Arduino

#include <TimerOne.h>
// This TimerOne.h library handles time-based interrupts

/**
 * In this program, we develop an application which executes on an Arduino 
 * and transmits the time and temperature at a periodic rate of around 10 
 * seconds across a Serial bus (USB) to the Host.
 * 
 * Uses the timer interrupts technique discussed on page 270 in 
 * "Exploring Arduino: Tools and Techniques for Engineering Wizardry" 
 * by Jeremy Blum
 * 
 * @version 7.0 2019-02-14
 * @author Addison Sears-Collins
 */
 
// Assign a name to the TMP36 sensor pin on the Arduino Uno
const unsigned int TEMP_SENSOR_PIN = A0;

// Flag used to stop the program
bool done = false;

// Used for capturing the time
unsigned long time;

// Used for capturing the temperature in Fahrenheit
float temp_fahrenheit;

/**
 *  Function runs only once, after each powerup or reset of the Arduino Uno
 */
void setup() {
  
  // Open the serial port and set the data transmission rate to 9600 bits 
  // per second. 9600 is the default baud rate for Arduino Uno.
  Serial.begin(9600); 
  
  // Show a welcome message as human-readable ASCII text
  Serial.println("SERIAL TRASMIT OF TEMPERATURE PROGRAM");
  Serial.println("This program transmits the time and temperature at a periodic");
  Serial.println("rate of ~10 seconds across a Serial bus (USB) to the Host.");
  Serial.println("Created by Addison Sears-Collins");
  Serial.println("");
  Serial.println("Press ! to end the program");
  Serial.println("");
  Serial.println("Recording temperature every 10 seconds...");
  Serial.println("");
  Serial.println("TIME, TEMPERATURE IN DEGREES FAHRENHEIT");

  // Interrupt: Set a timer of length 10000000 microseconds (10 seconds)
  Timer1.initialize(10000000);

  //Runs "isr_read_temperature" on each timer interrupt
  Timer1.attachInterrupt(isr_read_temperature); 
 
}

/**
 *  Main function
 */
void loop() {

  // Wait 100 seconds for temperature to stabilize
  // Temperature is being read in the background
  // via the interrupts
  delay(100000);

  while(!done) {    

    // Display the time and temperature
    display_time_and_temperature();
  
    // End program if sentinel is entered 
    end_program();    

    // Display time and temperature every 10 seconds
    delay(10000);
  }
  
  // Do nothing
  while (true) {}
}

/**
  * This function is the interrupt service routine.
  * It reads the voltage and converts to degrees Fahrenheit
  */
void isr_read_temperature() {
  
  // Read the voltage of the TMP36 sensor
  int sensor_voltage = analogRead(TEMP_SENSOR_PIN);
  
  // Calibrated. Equation taken from datasheet.
  // http://kookye.com/wp-content/uploads/samplecode/tempsensor.txt
  temp_fahrenheit = 5.1 + ((125 * sensor_voltage) >> 8);
}

/**
  * Function displays the time and temperature
  */
void display_time_and_temperature() {
  
  // Capture the time and covert to seconds
  time = millis() / 1000;

  // Display the time
  Serial.print(time); 
  Serial.print(" , ");
  // Println so the next line begins on a new line
  // Display the temperature in Fahrenheit
  Serial.println(temp_fahrenheit);   
}

/**
  * This function ends the program
  */
void end_program() {
  
  // Used for reading data from the serial monitor
  char ch;

  // Check to see if ! is available to be read
  if (Serial.available()) {     
  
    // Read the character
    // Serial.read() returns the first (oldest) character in the buffer 
    // and removes that byte of data from the buffer
    ch = Serial.read();    

    // End the program if an exclamation point is entered in the
    // serial monitor
    if (ch == '!') {
      done = true;  
      Serial.println("Finished recording temperature. Goodbye.");
    }
  }    
}