/*
 Keypad sketch
 prints the key pressed on a keypad to the serial port
*/
const int numRows = 4; // number of rows in the keypad
const int numCols = 3; // number of columns
const int debounceTime = 20; // number of milliseconds for switch to be stable
// keymap defines the character returned when the corresponding key is pressed
const char keymap[numRows][numCols] = {
 { '1', '2', '3' } ,
 { '4', '5', '6' } ,
 { '7', '8', '9' } ,
 { '*', '0', '#' }
};
// this array determines the pins used for rows and columns
const int rowPins[numRows] = { 7, 2, 3, 6 }; // Rows 0 through 3
const int colPins[numCols] = { 5, 8, 4 }; // Columns 0 through 2
void setup()
{
 Serial.begin(9600);
 for (int row = 0; row < numRows; row++)
 {
 pinMode(rowPins[row],INPUT); // Set row pins as input
 digitalWrite(rowPins[row],HIGH); // turn on Pull-ups
 }
 for (int column = 0; column < numCols; column++)
 {
 pinMode(colPins[column],OUTPUT); // Set column pins as outputs
 // for writing
 digitalWrite(colPins[column],HIGH); // Make all columns inactive
 }
}
void loop()
{
 char key = getKey();
 if( key != 0) { // if the character is not 0 then
 // it's a valid key press
 Serial.print("Got key ");
 Serial.println(key);
 }
}
// returns with the key pressed, or 0 if no key is pressed
char getKey()
{
 char key = 0; // 0 indicates no key pressed
 for(int column = 0; column < numCols; column++)
 {
 digitalWrite(colPins[column],LOW); // Activate the current column.
 for(int row = 0; row < numRows; row++) // Scan all rows for
 // a key press.
 {
 if(digitalRead(rowPins[row]) == LOW) // Is a key pressed?
 {
 delay(debounceTime); // debounce
 while(digitalRead(rowPins[row]) == LOW)
 ; // wait for key to be released
 key = keymap[row][column]; // Remember which key
 // was pressed.
 }
 }
 digitalWrite(colPins[column],HIGH); // De-activate the current column.
 }
 return key; // returns the key pressed or 0 if none
}