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Build keypad problem

Discussion in 'Electronic Basics' started by Jerry Ngu, Jan 2, 2004.

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  1. Jerry Ngu

    Jerry Ngu Guest

    Hello,

    I have a handheld device which requires a 3 x 5 matrix keypad to operate.
    Recently, the keypad went haywire, it's the contact based keypad build. I
    can't seem to find the replacement for it. So I reckon I want to build one
    replacement using buttons and circuit board in place of the printed matrix
    circuit. But I don't know how I should go about it. The keypad uses a 8
    conductor on the flat cable to generate the different keys pressed. Any
    ideas???

    Jerry
     
  2. It is a simple 3 by 5 matrix, like a DTMF (Touchtone) telephone
    keypad. The switches are wired in rows and columns. Look around for an
    old cordless phone and see if you can find a similar keypad. I scrapped
    about 30 last year, and threw away the keypads because no one wanted
    them. Grayhill and other companies make commercial grade matrix keypads,
    but they are not cheap. I have some of their 4 by 5 matrix, but not the
    3 by 5.
     
  3. Jerry Ngu

    Jerry Ngu Guest

    Hi Michael,

    Thanks for the quick reply ... I have gather the keypad matrix (through
    conductivity ...) by matching the 8 pin combination

    Key 1 = pin 2 and pin 7
    Key 2 = pin 6 and pin 7
    Key 3 = pin 7 and pin 8
    Key 4 = pin 1 and pin 2
    Key 5 = pin 1 and pin 6
    Key 6 = pin 1 and pin 8
    Key 7 = pin 2 and pin 3
    Key 8 = pin 3 and pin 6
    Key 9 = pin 3 and pin 8
    Key 0 = pin 4 and pin 6
    Up Key = pin 2 and pin 4
    Down Key = pin 4 and pin 8
    Escape Key = pin 2 and pin 5
    Shift Key = pin 5 and pin 6
    Enter Key = pin 5 and pin 8

    The original connector uses flat cable with printed conductor path. I will
    have to remove the connector from the circuit board and solder directly onto
    the 8 pin holes. But the problem still lies with the construction of the
    keypad matrix using normal electronic material (can't paint the circuit ??)
    .... Oh well, this is driving me nuts! hhahaha

    Hope to hear some good suggestions, thanks!!

    Jerry
     
  4. John Fields

    John Fields Guest

    ---
    If you take the keypad apart and follow where the 8 conductors go you'll
    find something like this: (View in a fixed-pich font like Courier)



    Y1 Y2 Y3 X1 X2 X3 X4 X5
    | | | | | | | |
    | | | | | | | |
    | | | | | | | |
    | | | | | | | |
    X---X---X---+ | | | |
    | | | | | | |
    X---X---X-------+ | | |
    | | | | | |
    X---X---X-----------+ | |
    | | | | |
    X---X---X---------------+ |
    | | | |
    X---X---X-------------------+


    where the X's denote the keypad switches. For example, if the X in the
    upper left hand corner is pressed, Y1 will be connected to X1 for as
    long as the key is held down, and if the key in the lower right hand
    corner is pressed, Y3 will be connected to X5.

    To build a keypad which functions the same as yours all you need to do
    is to use SPST momentary pushbuttons arranged in the same pattern as on
    your switch and make sure that the 8 conductor cable is wired to the
    switches the same way. If your keypad is a membrane keypad you may have
    some debouncing problems with the switches you substitute, so you may
    want to measure the bounce (using the good keys you have left) before
    you commit to buying 15 switches which might not work.

    The other thing you could do would be to determine the layout of the
    switch (as above) and then try to find a commercial unit that would fit
    in/on your device. If you can't find one, then maybe you could build an
    adapter to go between the connector of a new on which fits physically
    and where the old one plugged into.
     
  5. hamilton

    hamilton Guest

    Have you purchased the switches already ??

    The type of switches you buy will drive how you will wire them up.

    Also, a perf board from you local electronics hobby shop will do just fine.

    This is inside a box, right. No one will see the hack job. :)

    PS: Yes ,you can paint the circuit. ( google for copper paint )
     
  6. Jerry Ngu

    Jerry Ngu Guest

    Yeah, I envision that the keypad will look rather bulky once completed. The
    switches, do you mean any type of switches? Like those press type switches
    for door bells? I have been thinking about using those switches, but
    thinking about the wiring scares me ... heheheheh ..... that means I will
    need to solder at least 5 wires to pin 2, 6 and 8 respectively .... I wish
    those keypad manufacturer would have built some kind of generic keypad so
    that we could just wire them up ...

    Hmm ... I will have to go buy the copper paint ...

    Thanks !!
     
  7. hamilton

    hamilton Guest

    Hi Jerry,

    I guess you are very new to the idea of building something.
    This is such a basic project.

    Anyway, if you are in North America you can go to :

    <http://www.digikey.com/scripts/DkSearch/dksus.dll?Criteria?Ref=107336&Site=US&Cat=32834513>

    Select the 5 ma contact rating and the Mom(no) switch circuit.

    digikey also has keypads like the one you are lookiing for.
    They would look nice on the front of your package.

    Good Luck

    hamilton
     
  8. Jerry Ngu

    Jerry Ngu Guest

    Yes! I'm new to all this! hahaha ... I'm not from America, I'm from Malaysia
    actually. I have bought those switches, will try to hook it up and see if it
    works. I tried getting the copper paint from the electronic shops, but they
    don't even know there's such a thing!? I guess here is a little
    "unresourceful" .... anyway, I will have to make do with what I have now.

    Hey, you have been very very helpful, really appreciate it!

    Jerry
     
  9. Jerry Ngu

    Jerry Ngu Guest

    Yikes, I didn't see your message and I already bought 15 keys .... I will
    have to try and see if the connections work. Thanks for the diagram, very
    helpful for me ... will let you know if I manage to "fix" the old junk!

    Thanks again,
    Jerry
     
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