Matrix Keypad library
This page last updated September 04, 2013, at 11:42 AM by gratefulfrog
The Keypad library allows your Arduino to read a matrix type keypad. You can scavenge these keypads from old telephones or you can get them from almost any electronics parts store for less than $5 USD. They come in 3x4, 4x4 and various other configurations with words, letters and numbers written on the keys. This library is capable of supporting all of those.
First you need to get a piece of paper and draw the right hand diagram as you see it below. I've already written my pin numbers (1,2,3 across the bottom and 7,6,5,4 down the right side) which you can just leave off of your drawing. Next, you are going to use your Ohm meter to find out which pins are connected to which keys. The first thing to do is count how many pins are on your keypad (as seen in the photo below.) The photo is showing 14 pins though not all of the pins are used. Don't worry, once you've completed this procedure you will know which pins are unused and can be ignored.
/* Keypadtest.pde * * Demonstrate the simplest use of the keypad library. * * The first step is to connect your keypad to the * Arduino using the pin numbers listed below in * rowPins[] and colPins[]. If you want to use different * pins then you can change the numbers below to * match your setup. * */ #include <Keypad.h> const byte ROWS = 4; // Four rows const byte COLS = 3; // Three columns // Define the Keymap char keys[ROWS][COLS] = { {'1','2','3'}, {'4','5','6'}, {'7','8','9'}, {'#','0','*'} }; // Connect keypad ROW0, ROW1, ROW2 and ROW3 to these Arduino pins. byte rowPins[ROWS] = { 9, 8, 7, 6 }; // Connect keypad COL0, COL1 and COL2 to these Arduino pins. byte colPins[COLS] = { 12, 11, 10 }; // Create the Keypad Keypad kpd = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS ); #define ledpin 13 void setup() { pinMode(ledpin,OUTPUT); digitalWrite(ledpin, HIGH); Serial.begin(9600); } void loop() { char key = kpd.getKey(); if(key) // Check for a valid key. { switch (key) { case '*': digitalWrite(ledpin, LOW); break; case '#': digitalWrite(ledpin, HIGH); break; default: Serial.println(key); } } }
1. You can pretty much connect your keypad to any pins you would like. Be careful not to use the serial pins (0 and 1) if you are using them for communication.
2. If key presses seem to take a long time to show up then you are probably using long delay()'s in your code. The same thing can happen if you use too many small delay()s like delay(10).
3. Make sure you understand the pin mappings and have the keypad wired up to match. If you wired the pins incorrectly (and already soldered them in) then you may be able to fix it by redefining the pins and/or keymap to make your keypad work.
The library supports user defined pins and keymaps so it should not be necessary to change the library. If you do then you need to make sure you save your files back to the proper folder under \$ArduinoHome$\libraries\. You may also have to exit and restart the Arduino IDE software for it to recognize any new files in your library's folder.