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

tmp36

In this post, I’ll explain how to transmit time and temperature using a TMP36 sensor and an Arduino. The application that you will develop executes on an Arduino and transmits the time and temperature at a periodic rate of around 10 seconds across a Serial bus (e.g. USB) to a host computer (such as your personal laptop computer).

Requirements

Here are the requirements I created for this project:


  • The system must execute on an Arduino.
  • A temperature sensor connected to an Arduino must be calibrated.
  • The main program must use a Round Robin with interrupts design:
    • The temperature must be captured and converted to Fahrenheit.
    • The temperature must begin recording after the temperature has stabilized at room temperature.
    • The temperature must be recorded at a periodic rate of around 10 seconds (i.e. 10,000 milliseconds) at room temperature.
    • The temperature must then be recorded for 5 minutes at a periodic rate of around 10 seconds inside a refrigerator.
    • The temperature must then be recorded for 5 minutes at a periodic rate of around 10 seconds at room temperature.
  • The time and temperature must be transmitted across a Serial bus such as USB to my host.
  • The time and temperature data must be exported as a comma separated value file.
  • The comma separated value file must be read into a spreadsheet program (e.g. Microsoft Excel).
  • The temperature vs time must be plotted.

Hardware Design

The following components are used in this project. You will need:

Here is the diagram of the TMP36 temperature sensor:

tmp36_sensor_diagram

Here is the diagram of the hardware setup:

tmp36

Here are the steps for setting up the hardware of the Serial Transmit of Temperature system:

  • Step 1. Place the TMP36 sensor on the breadboard. Each lead of the sensor will be on a different rail section of the breadboard.
  • Step 2. Connect a jumper wire between the ground lead of the TMP36 sensor and the – rail of the breadboard.
  • Step 3. Connect a jumper wire between the – rail of the breadboard and the GND pin of the Arduino.
  • Step 4. Connect a jumper wire between the 5V pin of the Arduino and the + rail of the breadboard.
  • Step 5. Connect a jumper wire between + rail of the breadboard and the 5V lead of the TMP36 sensor.
  • Step 6. Connect a jumper wire between the middle output lead of the TMP36 sensor and the Analog 0 pin of the Arduino.
tmp36_sensor

Here are the steps for calibrating the TMP36 sensor:

We will use the One Point Calibration technique using a known temperature, 32°F, which is the freezing point of water.

  1. Crush several ice cubes and place in a plastic bag with some distilled water (Ada 2015).
  2. Close the bag up, making sure it is tied tight.
  3. Make sure the bag is completely dry on the outside and place it on top of the TMP36 sensor.
  4. Adjust temperature accordingly to calibrate.

Implementation

Here is the source code that you will need to load to your 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.");
    }
  }    
}

temperature_vs_time_tmp36_sensor
Graph of Temperature vs Time

Video