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Arduino Tutorials – Chapter 42 – Numeric Keypads

Learn how to use various numeric keypads with your Arduino.

This is chapter forty-two of our huge Arduino tutorial seriesUpdated 16/12/2013

Numeric keypads can provide a simple end-user alternative for various interfaces for your projects. Or if you need a lot of buttons, they can save you a lot of time with regards to construction. We’ll run through connecting them, using the Arduino library and then finish with a useful example sketch.

Getting Started

Numeric keypads are available from many retailers, and no matter where you get them from, make sure you can get the data sheet, as this will make life easier when wiring them up. Here are the two examples for our tutorial, from Futurlec (slow and cheap):

Arduino numeric keypads

 Again, the data sheet is important as it will tell you which pins or connectors on the keypad are for the rows and columns, for example the black keypad shown above. If you don’t have the data sheet – you will need to manually determine which contacts are for the rows and columns.

This can be done using the continuity function of a multimeter (the buzzer). Start by placing one probe on pin 1, the other probe on pin 2, and press the keys one by one. Make a note of when a button completes the circuit, then move onto the next pin. Soon you will know which is which. For example, on the example keypad pins 1 and 5 are for button “1″, 2 and 5 for “4″, etc…

Furthermore some keypads will have the pins soldered to the end, some will not. With our two example keypads, the smaller unit had the pins – and we soldered pins to the large white unit:

Arduino numeric keypads rear

At this point please download and install the keypad Arduino library. Now we’ll demonstrate how to use both keypads in simple examples. 

Using a 12 digit keypad

We’ll use the small black keypad from Futurlec, an Arduino Uno-compatible and an LCD with an I2C interface for display purposes. If you don’t have an LCD you could always send the text to the serial monitor instead.

Wire up your LCD then connect the keypad to the Arduino in the following manner:
  • Keypad row 1 to Arduino digital 5
  • Keypad row 2 to Arduino digital 4
  • Keypad row 3 to Arduino digital 3
  • Keypad row 4 to Arduino digital 2
  • Keypad column 1 to Arduino digital 8
  • Keypad column 2 to Arduino digital 7
  • Keypad column 3 to Arduino digital 6

If your keypad is different to ours, take note of the lines in the sketch from:

As you need to change the numbers in the arrays rowPins[ROWS] and colPins[COLS]. You enter the digital pin numbers connected to the rows and columns of the keypad respectively.

Furthermore, the array keys stores the values displayed in the LCD when a particular button is pressed. You can see we’ve matched it with the physical keypad used, however you can change it to whatever you need. But for now, enter and upload the following sketch once you’re satisfied with the row/pin number allocations:

And the results of the sketch are shown in this video.

So now you can see how the button presses can be translated into data for use in a sketch. We’ll now repeat this demonstration with the larger keypad.

Using a 16 digit keypad

We’ll use the larger white 4×4 keypad from Futurlec, an Arduino Uno-compatible and for a change the I2C LCD from Akafugu for display purposes. (We reviewed these previously). Again, if you don’t have an LCD you could always send the text to the serial monitor instead. Wire up the LCD and then connect the keypad to the Arduino in the following manner:

  • Keypad row 1 (pin eight) to Arduino digital 5
  • Keypad row 2 (pin 1) to Arduino digital 4
  • Keypad row 3 (pin 2) to Arduino digital 3
  • Keypad row 4 (pin 4) to Arduino digital 2
  • Keypad column 1 (pin 3) to Arduino digital 9
  • Keypad column 2 (pin 5) to Arduino digital 8
  • Keypad column 3 (pin 6) to Arduino digital 7
  • Keypad column 4 (pin 7) to Arduino digital 6
Now for the sketch – take note how we have accommodated for the larger numeric keypad:
  • the extra column in the array char keys[]
  • the extra pin in the array colPins[]
  • and the byte COLS = 4.

And again you can see the results of the sketch above in this video.

And now for an example project, one which is probably the most requested use of the numeric keypad…

Example Project – PIN access system

The most-requested use for a numeric keypad seems to be a “PIN” style application, where the Arduino is instructed to do something based on a correct number being entered into the keypad. The following sketch uses the hardware described for the previous sketch and implements a six-digit PIN entry system. The actions to take place can be inserted in the functions correctPIN() and incorrectPIN(). And the PIN is set in the array char PIN[6]. With a little extra work you could create your own PIN-change function as well. 

The project is demonstrated in this video.

Conclusion

So now you have the ability to use twelve and sixteen-button keypads with your Arduino systems. I’m sure you will come up with something useful and interesting using the keypads in the near future.

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Posted in arduino, COM-08653, numeric keypad, PIN, tronixstuff, tutorialComments (5)

Tutorial: Arduino and Numeric Keypads

Use numeric keypads with Arduino in chapter forty-two of a series originally titled “Getting Started/Moving Forward with Arduino!” by John Boxall – a series of articles on the Arduino universe. The first chapter is here, the complete series is detailed here. Any files from tutorials will be found here.

This is part one of two chapters that will examine another useful form of input – the numeric keypad; and some applications that hopefully may be of use.  Here is the example we will be working with:

It seems quite similar to the keypad from a 1980s-era Dick Smith Electronics cordless phone. Turning the keypad over we find seven pins:

Personally I like this type of connection, as it makes prototyping very easy using a breadboard – you just push it in. Looking at the back the pins are numbered seven to one (left to right). My example was from Futurlec of all places. You can also find types that have solder pads. At this point you need to download the data sheet.pdf, as it shows the pinouts for the rows and columns. At first glance trying to establish a way of reading the keypad with the Arduino does seem troublesome – however the basic process is to ‘scan’ each row and then test if a button has been pressed.

If your keypad has more than seven pins or contacts – and the data sheet was not supplied, you will need to manually determine which contacts are for the rows and columns. This can be done using the continuity function of a multimeter (the buzzer). Start by placing one probe on pin 1, the other probe on pin 2, and press the keys one by one. Make a note of when a button completes the circuit, then move onto the next pin. Soon you will know which is which. For example, on the example keypad pins 1 and 5 are for button “1”, 2 and 5 for “4”, etc…

In the interest of keeping things simple and relatively painless we will use the numeric keypad Arduino library. Download the library from here, copy the “Keypad” folder into your ../arduino-002x/libraries folder, then restart the Arduino IDE.

Now for our first example. From a hardware perspective you will need

  • An Arduino Uno or 100% compatible board
  • A numeric keypad
  • An LCD of some sort. We will be using an I2C-interface model. If you are unsure about LCD usage, please see this tutorial
  • If you don’t have an LCD – that’s ok. After installing the keypad library, select File>Examples>Keypad>Examples>HelloKeypad in the IDE.
Connect the keypad to the Arduino in the following manner:
  • Keypad row 1 to Arduino digital 5
  • Keypad row 2 to Arduino digital 4
  • Keypad row 3 to Arduino digital 3
  • Keypad row 4 to Arduino digital 2
  • Keypad column 1 to Arduino digital 8
  • Keypad column 2 to Arduino digital 7
  • Keypad column 3 to Arduino digital 6
Now for the sketch:

For the non-believers, here it is in action:


As you can see the library really does all the work for us. In the section below the comment “keypad type definition” we have defined how many rows and columns make up the keypad. Furthermore which digital pins connect to the keypad’s row and column pins. If you have a different keypad such as a 16-button version these will need to be modified. Furthermore you can also map out what the buttons will represent in the array “keys”. Then all of these variables are passed to the library in the function Keypad keypad = Keypad() etc.

Reading the buttons pressed is accomplished in void loop()… it reads the keypad by placing the current value into the char variable “key”. The if… statement tests if a button has been pressed. You can reproduce this loop within your own sketch to read values and then move forward to other functions. Let’s do that now in our next example.

Keypad Switch

Using our existing example hardware we can turn something on or off by using the keypad – replicating what can be found in some alarm systems and so on. Our goal with this example is simple – the systems waits for a PIN to be entered. If the PIN is correct, do something. If the PIN is incorrect, do something else. What the actions are can be up to you, but for the example we will turn on or off a digital output. This example is to give you a concept and framework to build you own ideas with.

The hardware is the same as the previous example but without the LCD. Instead, we have a 560 ohm resistor followed by an LED to GND from digital pin ten. Now for the sketch:

And the ubiquitous demonstration video:

This sketch is somewhat more complex. It starts with the usual keypad setting up and so on. We have two arrays, attempt and PIN. PIN holds the number which will successfully activate the switch, and attempt is used to store the key presses entered by the user. Users must press ‘*’ then the PIN then ‘#’ to activate the switch.

The comparison to check for accuracy is in the function checkPIN(). It compares the contents of PIN against attempt. If they match, the function correctPIN() is called. If the entered PIN is incorrect, the function incorrectPIN() is called. We also call the function incorrectPIN() in void setup to keep things locked down in case of a power failure or a system reset.

You can now see that such a complex device can be harnessed very easily, and could have a variety of uses. In part two, we will look at the 16-digit 

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Posted in arduino, learning electronics, lesson, microcontrollers, numeric keypad, tutorialComments (9)


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