Matrix keypad

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I'd like to connect a matrix 3x4 keypad (as the one on this page -> Arduino Playground - KeypadTutorial). I was just wondering, what kind of IC, or other electronic component(s) could I use, to reduce the amount of digital inputs I would need to use on Arduino? By the looks of it, without using anything I need to use 14 pins on Arduino. Is this correct?

Thanks,
Jerry

2

By the looks of it, without using anything I need to use 14 pins on Arduino. Is this correct?

No, it's multiplexed so for a 3X4 key matrix you need 3 lines for the outputs and 4 lines for the inputs, a total of 7.
You can reduce this by using logic chips.
A 74LS157 is a data selector and an 74LS139 is a demultiplexer. Use these together and you reduce the pin count down to 4.

3

Are there any schematics out there, that would help me understand how to connect such keypad to Arduino? Sorry for such dumb questions, but I'm a java programmer, with very limited knowledge of electronics. :slight_smile: