Arduino-Based Blue Box (Phone Phreaking)

Programming

The code for this new schematic in it's entirety can be found here on my pastebin.com profile. For the sake of this tutorial we will cover most of the key concepts of the syntax I have used. First of all the Arduino uses a programming language which is object-oriented; C++. This language is quite powerful and powers a lot of modern-day web site logic, micro-controllers, and much more!

Keypad

First we create a two dimensional array of integers that we use for holding the frequencies as specified per digit by the Wikipedia Blue Box page. We also set a duration as a typedef unsigned integer array. These integers are playback duration periods.

int bb[16][2] = { // MF 0,1,2,3,4,5,6,7,8,9,kp,st,2400+2600,kp2,st2,ss4 super<br>  {1300,1500},{700,900},{700,1100},      // 0,1,2
  {900,1100},{700,1300},{900,1300},      // 3,4,5
  {1100,1300},{700,1500},{900,1500},     // 6,7,8
  {1100,1500},{1100,1700},{1500,1700},   // 9,kp,st
  {2600,2400},{1300,1700},{900,1700},    // 2400+2600,kp2,st2
  {2400,2040},                           // ss4 Supervisory
};
<p>uint8_t bbdur[2] = {60,100};</p>

Next, we create an array matrix of keys as characters. These characters will be used each time a button on the keypad is pressed. We also set the rows and pins integer arrays.

char keys[4][4] = {<br>  {'1','2','3','a'},
  {'4','5','6','b'},
  {'7','8','9','c'},
  {'#','0','*','d'}
};
<p>byte rowPins[4] = {5,4,3,2}; //connect to the row pinouts of the keypad<br>byte colPins[4] = {9,8,7,6}; //connect to the column pinouts of the keypad</p>

Next we create a keypad object and a simple array of Tone objects. Since we are playing tones out of two pins at once, this just makes our lives simpler when writing and debugging the code.

Tone freq[2]; // array of Tone objects, now we can play as freq[0].play(); etc<br>Keypad keypad = Keypad(makeKeymap(keys),rowPins,colPins,4,4);

Reading Buttons and Playing Tones

In the setup() function, we need to set the freq[0] and freq[1] pins for output. This is simple. We also set the “pin mode” for the 2600 button and set an event-listener, which is a procButton() button processing custom function call. This is event-driven programming. This basically means that we “listen” for keys to be pressed, which would be an “event.” The main loop() function is what handles the events and listeners for us.

freq[0].begin(11); // Initialize our first tone generator<br>freq[1].begin(12); // Initialize our second tone generator
pinMode(10, INPUT); // 2600 button
keypad.addEventListener(procButton);

We have kept our main loop() method simple, which is good since it is constantly being called. The first line,

char button = keypad.getKey();

basically calls the getKey() method of the keypad object to see if and which key was pressed. The code,

if(digitalRead(10)==HIGH){ // play 2600Hz if top button pressed<br>  super(); // supervisory signalling
}

simply listens for voltage on pin 10 and if found, plays the 2600hz frequency by calling the custom supervisory signalling super() function. This is the very first function defined just below the loop() function. It is also the first function to call the custom single frequency playing sf() function as,

sf(2600,750);

The arguments we pass to this function are the frequency to be played, and the duration. After lexically assigning the frequency and duration to integer variables of the same names, the custom sf() function only calls a single play method on a single pin as,

freq[0].play(frequency,duration);

This is our first look at the tone synthesis play method from the Tone library. So, if you can imagine playing two tones, for multi-frequency would look similar, but with two pins, as,

freq[0].play(frequency,duration);<br>freq[0].play(frequency,duration);

And that is exactly what the custom multi-frequency playing mf() function does.

So how do we process each key press in the procButton() function? Using a case-switch logic. The constants “RELEASED,” “PRESSED,” and “HOLD,” (not “HELD” for some strange reason), are part of the keypad library and we can use the in a case-switch logic block as,

switch (keypad.getState()){<br>case RELEASED: // drop right away
  // do some stuff
  break;
case PRESSED: // momentary
  // do some stuff
  break;
case HOLD: // HELD (special functions)
  // do some stuff
  break;
}

And that's exactly what we do. Since the procButton() function is an event-handler called by the loop() function, we get a keypadevent object passed to it's handler procButton(). This object can be treated as a simple character – and we do that by simple subtracting the integer 48 from it to obtain which key was pressed from 0-9.

void procButton(KeypadEvent b){<br>  b -= 48;

Now we know which key was pressed and pass it to the mf() function which uses the multidimensional array bb[] which we created earlier to play the mf tones. You may have noticed that the KP (*) and ST (#) are not 0-9. This is correct, as they come through and after the subtraction are -13 and -6 respectively. The mf() function then handles these as,

}else if(digit==-13){<br>  digit = 12;  // *     
}else if(digit==-6){       
  digit = 14;  // #

This then plays the tones as they are assigned in the bb[] multi-dimensional array.

We have now covered all of the key concepts programmatically with this schematic (1), let's move onto the second schematic and how we can play WAV files which offer a completely different sound to our blue boxes.

Extra Features

This code provides a massive amount of extra features including recording digits into and array for playback, and different modes of operation. The code is very straight forward Arduino C++ code. Long press ‘A‘ to cycle through the different modes. Each time we change modes the notifyMode() function will pulse out a code of 440hz beeps to let us know which mode we are currently using. All modes are fully described on my weblog here or on the Wikipedia page for blue box specifications.

#include  // preprocessor directives (header files)<br>#define SDPIN 10    // SD Card Pin for SeeedStudio SD Card Shield
#include  // to play WAV files

if (!SD.begin(SDPIN)) {<br>  Serial.println("initialization failed!");   
}else{     
  Serial.println("initialization success!");   

}
tmrpcm.speakerPin = 9; //11 on Mega, 9 on Uno, Nano, etc   
tmrpcm.setVolume(3); // set volume here (test for distortion)

TMRpcm tmrpcm; // create sound playing object

tmrpcm.play("sounds/blusin01.wav");