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

1. ### Jerry NguGuest

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. ### Michael A. TerrellGuest

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
but they are not cheap. I have some of their 4 by 5 matrix, but not the
3 by 5.

3. ### Jerry NguGuest

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 FieldsGuest

---
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
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. ### hamiltonGuest

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 NguGuest

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. ### hamiltonGuest

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 NguGuest

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 NguGuest

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