Help with Matrix Keypad

Discussion in 'The Projects Forum' started by Nick Fury, Mar 6, 2007.

  1. Nick Fury

    Thread Starter New Member

    Mar 6, 2007
    2
    0
    So I've been digging around the web the past few days for some info about matrix keypads. I understand how they work and would like to use one with my project. I am attempting to build a waveform generator that varies its output based on which button on the keypad has been pressed.

    The schematics I am following indicate that I need separate switches for each of the outputs but I would really like to use a matrix keypad (it cuts down on cost as I already have one available). If I simply plug in the matrix keypad in place of the existing switches then there are going to be unwanted shorts in the circuit.

    I would like to find a hardware solution to this problem so that I can either isolate the each of the swithces in the matrix keypad or come up with a way to "decode" the output of the keypad so that I have individual wires and grounds.

    I simply just don't know what kind of IC or component I should be looking for and/or using to make this work.

    Thank you for any help you can provide as it is greatly appreciated.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    You could try controlling transistor switches with the o/p of a matrix decoder & demultiplexer, but it might be simpler to use a microcontroller.
     
  3. Nick Fury

    Thread Starter New Member

    Mar 6, 2007
    2
    0
    Surely a microcontroller can't be the simplest solution though. There has to be a hardware solution to this that fits the bill.
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I guess it depends on how we define "simple." For a 4x4 matrix, one could use an MM74C922 encoder to get an 4 bit number representing which button was pushed. 18 pins to solder so far. We could rout the 4 bits to a 74154 demultiplexer to get sixteeen control lines. Another 24 pins to solder. If you need switches instead of 0v and 5v levels, then something like 4ea 4066 chips will be needed. 56 more pins to solder.

    If it were my project I would at least take a look at the microcontroller option.
     
  5. lightingman

    Senior Member

    Apr 19, 2007
    374
    22
    Yes !!! I agree..Do it with a PIC, you can then rearange the keypad into any order just by changing a bit of code.You can then send the data from each keypress as binary, HEX, serial , or seperate outputs.You can do what you like with the data plus so much more !!!Daniel.
     
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