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DIY Thermal Imaging System for under $200

One of the first things we heard when we started talking to firefighters about the potential for a heads-up display was “give us more and cheaper access to thermal imaging.” Being the tinkerers that we are, we thought we’d try to cobble something together with an Arduino and some off-the-shelf sensors. Luckily, some other folks in the Arduino community forged the way, so we didn’t have to start from scratch. Our thanks to Stephan Martin for his original write-up detailing his thermoscanner.

What we used:

• 1 - Arduino Uno
• 1 – Breadboard
• 1 – Mini Breadboard
• A Bunch of Breadboard Jumpers
• 2 – Micro Servos
• 1 – Pan and Tilt Bracket Kit
• 1 – Devantech TPA81 8×1 Thermopile Array
• 1 – Random box for mounting everything

Putting it together:

I’ll admit, this was my first Arduino project. Because of that I decided it would probably be safer to use the breadboard rather than soldering anything, that turned out to be a good idea as I didn’t get everything wired up correctly the first time around. To help you avoid the same mistakes I made I created a wiring schematic that should show you where everything plugs in.

Thermal Imaging Camera Schematic

To make the build a little easier, I mounted the mini-breadboard on the pan and tilt brackets and plugged the thermopile array into the mini-breadboard. That also made it easier to wire the thermopile to the Arduino since I didn’t have to solder or try to fashion a suitable connector. The last thing left to do is to mount the pan servo. I went for a very low-tech solution: cut a small hole in a heavy cardboard box just big enough for the servo. If you go this route as well I’d recommend using a small screw in the mounting bracket on the servo to add some stability, otherwise the servo will wiggle itself out of your mount.

Making it work:

Once you have your thermal imaging camera assembled you’ll need some software to make it all work. Before we get to the actual software now is a good time to test that you have the thermopile array wired correctly. My thanks to Jason Winningham in the Arduino Forum for posting the following code to test the TPA81:

// prototype code for interfacing Devantech TPA81 thermopile array
// http://www.robot-electronics.co.uk/htm/tpa81tech.htm
//
// Jason Winningham
// 27 june 2007
// Reposted by Tanagram
// http://spill.tanagram.com/2010/11/24/diy-thermal-imaging/
// Made available under the GNU Lesser General Public License (LGPL)
// http://www.gnu.org/licenses/lgpl.html
// November 24, 2010

#include <Wire.h>
#define TPA81ADDR (0xd0>>1)

void setup()
{
  Wire.begin();        // join i2c bus (address optional for master)
  Serial.begin(9600);  // start serial for output
  Serial.print("starting TPA81 test\n");
} 

void loop()
{
  byte b;
  int i;

  for (i=1; i<=9; i++)
  {
    Wire.beginTransmission(TPA81ADDR);
    Wire.send(i);
    Wire.endTransmission();

    Wire.requestFrom(TPA81ADDR, (int) 1);

   while(Wire.available() < 1)
   { ; }

    b = Wire.receive(); // receive a byte as character 

    Serial.print(b, DEC);
    Serial.print(" ");
  }
  Serial.println("");

  delay(2000); // Sample as low as 1ms
}

Load that into your Arduino, open the Serial Monitor, and you should see a series of 9 integers returned every two seconds. Those will be the ambient temperature and the temperature from each of the eight thermopiles in the array, all in degrees Celsius.

Once you have confirmed that your thermopile array is working correctly, it’s time to install the thermoscanner software. Before you load the Arduino and Processing sketches you’ll need the AFSoftSerial library for Arduino. There are two parts to the software, the Arduino code and an additional Processing sketch that controls the thermoscanner and displays the results.

Thermoscanner Arduino Sketch:

//test by d2k2 24.09.2009
// Reposted by Tanagram
// http://spill.tanagram.com/2010/11/24/diy-thermal-imaging/
// Made available under the GNU Lesser General Public License (LGPL)
// http://www.gnu.org/licenses/lgpl.html
// November 24, 2010

#include <Servo.h>
#include <AFSoftSerial.h>

#include <Wire.h>
#define TPA81ADDR (0xd0>>1)

Servo myServoPan;  // create servo object to control a servo
Servo myServoTilt;  // create servo object to control a servo 

AFSoftSerial mySerial =  AFSoftSerial(3, 2);

char CurrentServo;
int value;

int valueA;          //Storage
int valueB;

int fresh = 0;

int Read = 0;
int runVal = 0;

void setup()
{
  Wire.begin();        // join i2c bus (address optional for master)
  myServoPan.attach(9);  // attaches the servo on pin 9 to the servo object
  myServoTilt.attach(10);  // attaches the servo on pin 10 to the servo object 

  pinMode(13, OUTPUT);
  Serial.begin(57600);

  Serial.println("Scanturm V0.1");
}

void loop()                     // run over and over again
{

  get_keyboard_commands();

}

void get_keyboard_commands() {

  myServoPan.write(valueA);
  myServoTilt.write(valueB);

  if ( Serial.available()) {

    // read in a string
    Read = Serial.read();

    if (Read == 200){
      runVal = 0;
     // Serial.println("Reset");
    };

   switch (runVal) {
    case 0:
      runVal = 1;
      break;
    case 1:
      valueA = Read;
      runVal = 2;
      break;
    case 2:
      valueB = Read;
      runVal = 3;
    case 3:   

      SendTPA();

      /*
      Serial.print(": ");
      Serial.print(val);
      Serial.println("$");
      */
      //runVal = 1;
      break;
   }

 }

}

void SendTPA(){

  //Send the TPA81 Data back to the PC:

   byte b;
  int i;

  for (i=1; i<=9; i++)
  {
    Wire.beginTransmission(TPA81ADDR);
    Wire.send(i);
    Wire.endTransmission();

    Wire.requestFrom(TPA81ADDR, (int) 1);

   while(Wire.available() < 1)
   { ; }

    b = Wire.receive(); // receive a byte as character 

    Serial.print(b, DEC);
    Serial.print(";");
  }
  Serial.println("");
}

Thermoscanner Processing Sketch:

//d2k2 24.09.2009  shows values from the TPA81
//prestage for putting the sensor on the scan turrent

// Reposted by Tanagram
// http://spill.tanagram.com/2010/11/24/diy-thermal-imaging///
Made available under the GNU Lesser General Public License (LGPL)
// http://www.gnu.org/licenses/lgpl.html
// November 24, 2010

import processing.serial.*;

Serial myPort;  // Create object from Serial class
int lf = 10;    // Linefeed in ASCII
String myString;
int[] val = {1,1,1,1,1,1,1,1,1};
int MaxT=100;
int MinT=20;
int pan = 40;
int tilt = 0;
String[] list = null;

int MaxT2 = 0;
int MinT2 = 255;

boolean result = false;
boolean run = false;

long time;
long lastrun = 0;
long runT;

void setup()
{
  size(400, 400);

  String portName = Serial.list()[1];
  myPort = new Serial(this, portName, 57600);
  myPort.buffer(1);

}

void draw()
{

  time = millis();
  runT =  lastrun - time;

  String myTest = "";

  if ( myPort.available() > 0) {  // If data is available,

    myString = myPort.readStringUntil(lf);
    if (myString != null)
    {
      list = split(myString, ';');
      myTest = list[0];
      if(int(myTest)>0)
      {

        result = true;

        val[1] = int(list[8]);
        val[2] = int(list[7]);
        val[3] = int(list[6]);
        val[4] = int(list[5]);
        val[5] = int(list[4]);
        val[6] = int(list[3]);
        val[7] = int(list[2]);
        val[8] = int(list[1]);
        val[0] = int(list[0]);

        //check for new max/min events

        if(MaxT2min(val))
        {
          MinT2 = min(val);
        }

        //Draw another Line, right at the Pan Position

         //Pan is about everywhere from 10 to 170
         //so i need to update every Pan Pixel and just try it like that now

         float Col = 0;

         for(int i = 1;i<9; i = i+1){
           Col = map(val[i],MinT,MaxT,0,255);
           color drp = color(Col,Col,Col);
           for(int i2 = 1; i2 < 5; i2 = i2+1){
           set(pan+pan,    (i*4)+75+i2+tilt+tilt+4*i-100,drp);
           }
           for(int i2 = 1; i2 < 5; i2 = i2+1){
             set(pan+1+pan,(i*4)+75+i2+tilt+tilt+4*i-100,drp);
           }

         }

    }
  }

  //background(255);             // Set background to white

//Draw them 9 Pixels in a line:
/*
int Size = 45;
         float Col = 0;
        for (int i = 1; i < 9; i = i+1) {            rect((Size*i)-Size+5, 5, Size, Size);            Col = map(val[i],MinT,MaxT,0,255);            fill(0,0,Col);         } */    } if(millis()>lastrun)
{
if(run == true)
{
  //Now i need to check if i got a result:
  if(result == true)
  {
    //Now i need to check if im at the end of my motion:
    if(pan < 150)
    {
      //Now i can move
      pan = pan + 1;
      SetServo();
      lastrun = millis()+100;
    }
    else
    {
      run = false;
    }
  }
}
}  

}

void keyPressed() {
  if( key == '6'){
   pan = pan+1;
   SetServo();
   println("Pan: " + pan);
   println("Tilt: " + tilt);
  }

  if( key == '4'){
   pan = pan-1;
   SetServo();
   println("Pan: " + pan);
   println("Tilt: " + tilt);
  }

  if( key == '8'){
   tilt = tilt-2;
   SetServo();
   println("Pan: " + pan);
   println("Tilt: " + tilt);
  }

  if( key == '2'){
   tilt = tilt+2;
   SetServo();
   println("Pan: " + pan);
   println("Tilt: " + tilt);
  }

  if( key == '5'){
   SetServo();
   println("Pan: " + pan);
   println("Tilt: " + tilt);
  }

  if( key == '1'){
   pan = 40;
   SetServo();
   println("Pan: " + pan);
   println("Tilt: " + tilt);
  }

  if( key == '3'){
   run = true;
  } 

}

void SetServo(){
    result = false;
    myPort.write(200); //init
    myPort.write(tilt); //tilt
    myPort.write(pan); //pan
    delay(100);
    myPort.write(80); //trigger read
}

Both sketches come from Stephan Martin’s write-up of his thermoscanner project. After the sketch is loaded up to your Arduino you should be able to run the Processing sketch and start your first thermal imaging scan. To control your thermal imaging scanner use the number keys on your keyboard:

• 1 – Reset pan servo to 40°
• 2 – Increase tilt servo by 2°
• 3 - Run the scanner
• 4 - Reduce pan servo by 1°
• 5 - unused
• 6 - Increase pan servo by 1°
• 7 - unused
• 8 - Increase tilt servo by 2°
• 9 - unused

To run a complete scan requires two passes, and takes these steps:

1. Make sure the Processing sketch is running
2. Press 1 and wait for the pan servo to reset to 40°
3. Press 3 and wait until the pan servo completes it’s rotation
4. Press 1 to reset the pan servo to the start position again
5. Press 8 to increase the tilt servo by 2°
6. Press 3 to start the next pan rotation

After that you should have a complete scan without any gaps. If you can control the servos with the keyboard but the scan doesn’t run when you press 3 double check your wiring for the thermopile array. If the Processing sketch doesn’t receive any input from the thermopile array it won’t execute the scan.

The output

Here is what the output should look like.

Thermal Imaging Scan

But what does this all mean?

Quite honestly, we’re not entirely sure yet. But we have a much better understanding of how thermal imaging works, and that means we’ll be better able to determine if thermal imaging can be a realistic piece of what is going to go into a heads-up display for firefighters.

Disclaimer and Licensing

While this project is functional it is prone to “seizures” and could use improvement. The source code and plans above are available to all being made available to all under the GNU Lesser General Public License (LGPL). If you use this please maintain the references to Tanagram and the original authors of the code above. Also, if you make improvements we’d love to know about it. You can either post a comment, link to this post, or send an email to contact [at-symbol] tanagram.com. Have fun!

Image Gallery

Posted by Timothy Mills on November 24, 2010