Uses an Adafruit 3x4 Keypad

// Pin allocation for keypad COLUMNS
#define Col1 4 // pin for Col 1
#define Col2 2 // pin for Col 2
#define Col3 6 // pin for Col 3
#define Col4 9 // pin for Col 4 (only present on 4x4 keypad)
// Pin allocation for keypad ROWS
#define Row1 3 // pin for Row 1
#define Row2 8 // pin for Row 2
#define Row3 7 // pin for Row 3
#define Row4 5 // pin for Row 4
// pin allocations for tone outputs
#define tone1Pin 12 // pin for tone 1
#define tone2Pin 13 // pin for tone 2
#define NoKey 0xff // no key pressed
const byte columns[] = {Col1, Col2, Col3}; // list of all columns
const byte rows[] = {Row1, Row2, Row3, Row4}; // list of all rows
const byte NumCols = sizeof(columns) / sizeof(byte); // calculate number of columns
const byte NumRows = sizeof(rows) / sizeof(byte); // calculate number of rows
byte LastKey = NoKey; // last key pressed

int DTMF[][2] = {
{697, 1209}, // frequencies for key 1
{770, 1209}, // frequencies for key 4
{852, 1209}, // frequencies for key 7
{941, 1209}, // frequencies for key *
{697, 1336}, // frequencies for key 2
{770, 1336}, // frequencies for key 5
{852, 1336}, // frequencies for key 8
{941, 1336}, // frequencies for key 0
{697, 1477}, // frequencies for key 3
{770, 1477}, // frequencies for key 6
{852, 1477}, // frequencies for key 9
{941, 1477}, // frequencies for key #
{697, 1633}, // frequencies for key A
{770, 1633}, // frequencies for key B
{852, 1633}, // frequencies for key C
{941, 1633}, // frequencies for key D
};
int ReadKeyPad()
{

byte result = NoKey; // no key pressed
for (int c = 0; c < NumCols; c++) digitalWrite(columns[c], HIGH); // set all columns HIGH
for (int c = 0; c < NumCols; c++) { // scan each column
digitalWrite(columns[c], LOW); // set column LOW
for (int r = 0; r < NumRows; r++) { // scan each row for LOW on any row
if (digitalRead(rows[r]) == LOW) {
delay(50); // in case of bounce
if (digitalRead(rows[r]) == LOW) return c * 4 + r;
}
}
digitalWrite(columns[c], HIGH);
}
return result;
}
void setup()
{
// initialise row readers
for (int i = 0; i < NumRows; i++) pinMode(rows[i], INPUT_PULLUP); // Set row drivers to INPUT
// initialise column drivers
for (int i = 0; i < NumCols; i++) {
pinMode(columns[i], OUTPUT); // Set column drivers to OUTPUT
digitalWrite(columns[i], HIGH);
}
pinMode(tone1Pin, OUTPUT); // Output for Tone 1
pinMode(tone2Pin, OUTPUT); // Output for Tone 2
Serial.begin(9600); // Set serial port speed
}
void loop()
{
byte key = ReadKeyPad(); // read any key being pressed
if (key != LastKey) // key has changed
switch (key) {
case NoKey: break; // nothing to do
default: // play tones
Serial.print("Pressed "); Serial.println(key); // Debug only
playDTMF(key, 200); // changes tone length
break;
}
LastKey = key; // remember last key pressed
}
void playDTMF(byte digit, unsigned long duration) {
// Play the DTMF digit for duration millisecs
unsigned long tone1delay = (500000 / DTMF[digit][0]) - 10; // calculate delay (in microseconds) for tone 1 (half of the period of one cycle). 10 is a fudge factor to raise the frequency due to sluggish timing.
unsigned long tone2delay = (500000 / DTMF[digit][1]) - 10; // calculate delay (in microseconds) for tone 2 (half of the period of one cycle). 10 is a fudge factor to raise the frequency due to sluggish timing.
unsigned long tone1timer = micros();
unsigned long tone2timer = micros();
unsigned long timer = millis(); // for timing duration of a single tone
while (millis() - timer < duration) {
if (micros() - tone1timer > tone1delay) {
tone1timer = micros(); // reset the timer
if (digitalRead(tone1Pin) == HIGH) digitalWrite(tone1Pin, LOW); else
digitalWrite(tone1Pin, HIGH); // toggle tone output
}
if (micros() - tone2timer > tone2delay) {
tone2timer = micros(); // reset the timer
if (digitalRead(tone2Pin) == HIGH) digitalWrite(tone2Pin, LOW); else
digitalWrite(tone2Pin, HIGH); // toggle tone output
}
}
digitalWrite(tone1Pin, LOW);
digitalWrite(tone2Pin, LOW);
}