control button array

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I need an inexpensive array of (real) pushbuttons
that are 5 x 5 plus 2 col of 12 rows. What would
you recommend?


Ideally they would be self scanned and deliver a
code for 'down' and a code for 'up' via serial line.

I have used the IEE panels in the past for this.

Thanks,

Rick
Merrill


Re: control button array
On Mon, 10 Nov 2003 21:19:10 GMT, Rick Merrill

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I'm not really clear what you're saying above,
25 + 24 PBs?

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I'd use a PIC (or similar) dedicated to just the
keyboard task using  two 8 bit ports to do the
lot on an 8 * 8 matrix, the serial comms could
then be RS232, synchronous, or bit bashed
and the PIC would handle debouncing, shift
keys, double keypress etc. Simple,
configureable, selfcontained and cheap

Mike Harding


Re: control button array
Nah. There's a simple part that does keyboard matrix w/debounce:

Check out the MM74C923N
Datasheet at http://www.fairchildsemi.com/ds/MM/MM74C923.pdf

Gary

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Re: control button array
On Mon, 10 Nov 2003 17:11:51 -0500, "Gary Desrosiers"

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Yep, that's a good chip I first used it (or maybe
it's younger brother in about 85?) but it will only
handle 20 keys, not enough for the OPs 49 keys.

Mike Harding


Re: control button array
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Thanks for all the good feedback.

How about I get a $10 keyboard at Office Depot and hook
that up to scan 7x7 ?  -  RM


Re: control button array
On Tue, 11 Nov 2003 00:50:28 GMT, Rick Merrill
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If you mean a PC keyboard? Well you could but you
would have to butcher it quite a bit and then actually
hook your push buttons up in the location/arrangement
you require which might? take a lot of time and effort.
And then you would need to interface to it (although
it's a well documented protocol) and interpret the
scan codes etc. I think it needs a clock as well?
Personally I'd still go for the dedicated PIC solution
providing you can write that sort of software and do
the, fairly simple, wiring required.

Mike Harding


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