Arduino 3 Wire Matrix Keypad
Intro: Arduino 3 Wire Matrix Keypad
Keypad connected with only 3 wires to Arduino.
Background:
A matrix keypad can be connected to an Arduino board so that numerical data can be entered by the user.
Instructions exist in various forums on how to do this. The main problem is that this usually uses up a total of 7 of your digital input/output pins.
The problem:
For me this is a big problem as I want these pins free to control external devices such as solenoid valves and actuators. I also need some to send data to a serial LCD display.
Options are either
a) Use an Arduino Mega with lots more pins or
b) Find a way of interfacing a keypad using less input pins.
Solution:
By using ONE single analog input pin and a grid of resistors, we can wire up the buttons on the keypad such that when each is pressed a different voltage is sent to the analog input pin.
Although it is a hassle wiring up all the resistors, the big advantage is that all your digital pins remain free to be used for other things.
This has been described before on AVR forums but I have adapted it for Arduino and written some code for you to get started.
STEP 1: Identify the Keypad Pins
Keypad can be considered to have 3 "columns" and 4 "rows" - see photo.
First step is to work out which solder terminal represents each row and which represents each column. Write everything down as you go along, very easy to mix everything up.
This has been described and you need to follow the instructions on how to do this given in this Arduino keypad tutorial:
http://www.arduino.cc/playground/Main/KeypadTutorial
STEP 2: Wiring Up the Resistors
As you can see there is one single wire to analog input pin 0 on the Arduino plus a connection to +5V on the Arduino and also one to GND (ground)....3 wires in total.
Having worked out your rows and column wires, you need to follow this diagram.
I use ribbon cable as it makes things (relatively) neat.
The tiny capacitor is there to prevent interference induced in the wires being transmitted as a voltage to the analog input producing errors.
STEP 3: Test It!
There will be slight variations depending on tolerances of the resistors but the values you get should be roughly similar to those which I obtained.
STEP 4: Write Software to Read Your Kepad
In this example, when you press a key, the value on each key will appear in the serial viewer window (i.e. 0 - 9) on your PC.
You can see that there has to be some code that takes the value, then waits for you to release the key before continuing, to prevent a whole sequence appearing of the same value.
The code is a bit clunky but it works. You will have to adapt this for your own applications but it should get you started.
The variable "keypressed" is the value of 0 - 9 which you can then use in the rest of your program.
Have fun.
26 Comments
wimpiw 8 years ago
i want to ask a question..
i used '<Keypad.h>'
but when i compiled error come and said: keypad.h No such file or directory..
why? can you help me
hoosseina 5 years ago
hoosseina 5 years ago
hossam12116 7 years ago
very nice
aporras bonet 8 years ago
Really useful project for all arduino users. So easy to make in a couple of hours.
Made it in a breadboard, passed to a protoboard and worked at first. Awesome !!!
Thanks a lot for so simple and useful arduino project XD
kenneth.natera.1 9 years ago
did u use 1% tolerance resistors?
I got different values on the ADC measures
tayebm 9 years ago
i made a prototype for my project thanks so much for the ez keypad that gives me free pins for other stuff :D
it was so helpful
i had to change some resistors because i didn't have but it worked well
thank you so much
and sorry for my bad English
Tayeb
macogala 10 years ago
Hi! First of all thank you because this may be really useful.
Second, I have a question. I haven't tried this project yet, but as far as I've understood it, it's nothing but a Voltage Partitor. Now, I wonder if you have provided some kind of control regarding the possibility of multiple keys pressed, because I think there may be some problems if I press 2 or more keys at the same time.
In this case, obviously, the voltage wouldn't split as it is supposed to be, but I guess it may even be splitted in such a way that, for the Arduino, it corresponds to a completely different key. Am I right? And if so, have you thought about a solution regarding this?
Thank you very much,
Marco
osdoyi 10 years ago
marcoboers 10 years ago
Do you have it working in the mean time? And what resistor values did you use?
Thanks in advance
osdoyi 10 years ago
Yeap I solved it. In schematics I add one more resistor in this order: 1000 ohms, 820
ohms, 1000 ohms, and 820 ohms.
marcoboers 10 years ago
Thanks I'll try this out.
tumbledown 11 years ago
its a wet and windy Sunday here in the UK and nothing else to do?
roachburn 12 years ago
Dominion-Network 12 years ago
thiagottjv 12 years ago
And the resistors? how did you calculate the sizes?
XenonJohn 12 years ago
The resistor values were borrowed from a post on similar topic on the AVR forums.
Best wishes
John
XenonJohn 12 years ago
If you turn it over you see that several of the apparent solder terminals don't do anything and there are 7 active terminals.
budabob07 12 years ago
fennecfanatic 13 years ago