That won't work for a professional commercial product, but if you are
building just a couple of them for hobby, then OK.

I insist in pointing out that the conventional method works perfectly
well for multiple simultaneous key presses and it is not hard at all
implementing it.

With your keyboard you are limited to detect keys all in the same row or
column, not diagonal etc. With the conventional method you can detect
any number of keys in the same row or column, or in any arrangement as
long you don't press keys that make all the three vertexes of an "L" shape.

Besides, it is possible to share four pins of the MCU between the
keyboard and an LCD module.


Best regards,

Isaac



Em 3/4/2013 22:47, Allen Mulvey escreveu:
> These were on sale for $0.79 USD. Now they are now $1.49.
> They have 2 key markings for fire, police, and ambulance as
> well as 3 green LED, 1 yellow, and 2 red. The size is such
> that you can shave off about 3/32" and fit it into clear
> covered exterior outlet box. The face is printed on the back
> of a clear plastic sheet set into the front so you can peel
> it off and make your own if you wish.
>
> http://www.goldmine-elec-products.com/prodinfo.asp?number=3DG1
> 7927
>
> Allen
>
> -----Original Message-----
> From: piclist-bounces@mit.edu
> [mailto:piclist-bounces@mit.edu] On Behalf Of Isaac Marino
> Bavaresco
> Sent: Wednesday, April 03, 2013 8:53 PM
> To: Microcontroller discussion list - Public.
> Subject: Re: [PIC] Pull Up Resistors
>
> With this arrangement you will need some unusual switches
> (three
> terminal make-make)
>
> And with the conventional method it is also possible to
> detect multiple
> simultaneous presses.
>
>
> Isaac
>
>
> Em 3/4/2013 19:25, Allen Mulvey escreveu:
>> Thank you all for the excellent information and resources.
> I
>> had checked Microchip and MikroElektronica sites and found
>> nothing. I missed the significance of the current rating
> for
>> the internal pullups.
>>
>> I have been experimenting with a slightly different kind
> of
>> matrix keypad. Instead of shorting row and column, it
>> grounds both. This eliminates the need to scan and allows
>> the selection of multiple key presses although not all may
>> be unique. I think much of the problem I have seen has
> been
>> caused by capacitance. Earlier I didn't think about the
> R-C
>> timer effect. If I connect the keypad with a foot of cat-5
>> cable the 20k resistors work fine. If I use 6" of ribbon
>> cable 20k is too big but 4k7 or slightly less works fine.
>> There also appears to be a difference depending on which
> end
>> of the cable the resistors are attached although I have
> not
>> tested this very well.=20
>>
>> Thanks again,
>> Allen
>>
>>
>>

--=20
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