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'keypad'
2002\08\25@121037 by guy

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apology for those who received this earlier!

Hi All,

I recently made a pcb of 8x8 keypad with two "E"s facing eachother at each
keypad
point.  Somehow, the port always gives value when it is
supposed to be "0" since there is no keypress.  Is this a capacitance or
resistance problem?  any help greatly appreciated.


Yansong

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2002\08\25@122558 by Pic Dude

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Why do you say that it should be "0"?  In general though,
you should not leave the inputs floating, cause the value
seen at the port will be unpredictable, though I've found
that it tends to assume the "1" state most of the time.

You should explicitly set it to the default you want with
pull-up or -down resistors (you can use the PIC built-in
weak pull-ups).  Generally I keep the weak pull-ups on and
switch to ground, so the processor sees "1" until the switch
is pressed.

Cheers,
-Neil.



> {Original Message removed}

2002\08\26@075206 by guy

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Thanks for the feed back.  I did left the input floating.  The chip is port6
of a TI msp430F413.  It doesn't has built-in pull-ups.  Is it right for a
pull-down to be implemented as the following:


port---------|-----[Resistor]------ground
            |
            |
            input

yansong
----- Original Message -----
From: Pic Dude <spam_OUTpicdudeTakeThisOuTspamPILOTTOOLS.COM>
To: <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
Sent: Sunday, August 25, 2002 9:24 AM
Subject: Re: keypad


{Quote hidden}

> > {Original Message removed}

2002\08\26@100223 by Pic Dude

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Not familiar with the TI chip.  However, where is the
switch in your circuit drawing below?  You should be
using one of these...

         +Vcc
           |         switch
           R           |
           |         --'--
port -------o---------o   o---.
                             |
                             |
                            Gnd


OR...


                  switch    +Vcc
                    |        |
                  --'--      |
port -------o------o   o------'
           |
           R
           |
          Gnd



> {Original Message removed}

2002\08\26@193111 by guy

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I have solved my problem with 1K pull-down.  Many thanks to Pic Dude and
Fancisco.

Yansong


----- Original Message -----
From: Pic Dude <picdudespamKILLspamPILOTTOOLS.COM>
To: <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Sent: Monday, August 26, 2002 7:01 AM
Subject: Re: keypad


{Quote hidden}

> > {Original Message removed}

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