Trouble with 4x4 Telephone Keypad

J

Jack// ani

Guest
Hi all,

I'm making a 4x4 keypad for a DTMF dialer using on/off tactile
switch. Problem is Row and Column has internal pullup resistors, so
that to generate a tone you have to short the corresponding Row/Column
and pull it down to ground. Before this I have experienced with simple
keypad where no ground is required, I'm totally confused as how to
proceed. Please help me.

Thanks in advance
 
Thanks all. Actually DTMF chip (UM95089) I'm using is old, discontinued
part. And it was really hard to find the datasheet around, lucky enough
here, I got one :). They have suggested keypad schematic(Figure 1)
which I can't understand! I've uploaded the datasheet here
http://www.geocities.com/nospam4u_jack/UM95089.pdf , will you please
have a look at this problem?

Thanks again
 
Lord thanks a lot for reply. I'm very sorry I didn't stated the problem
clearly. Pullup resistors (20K -10K) are internal to the chip and are
*not* on my keypad. Please refer to page 5 of the datasheet. Keypad is
just a simple arrangement of switches in 4x4 matrix, which is shorting
the corresponding row and column. Problem here is after pressing the
switch I've to connect the shorted terminal to ground, in order to
generate a tone. I want to get the tones only by pressing switches
itself. I know there are many chips around which can easily solve my
problem, but I'm interested to do with this one.

Thanks again
 
On 18 Apr 2005 11:05:47 -0700, "Jack// ani" <nospam4u_jack@yahoo.com>
wrote:

Lord thanks a lot for reply. I'm very sorry I didn't stated the problem
clearly. Pullup resistors (20K -10K) are internal to the chip and are
*not* on my keypad. Please refer to page 5 of the datasheet. Keypad is
just a simple arrangement of switches in 4x4 matrix, which is shorting
the corresponding row and column. Problem here is after pressing the
switch I've to connect the shorted terminal to ground, in order to
generate a tone. I want to get the tones only by pressing switches
itself. I know there are many chips around which can easily solve my
problem, but I'm interested to do with this one.
Click to expand...
---
Unfortunately, with the array of 16 SPST tactile switches you propose
to use, there's no way you're going to get what you want.

--
John Fields
Professional Circuit Designer
 
I earlier also posted it but never appeared on the board, so posting
again.....

Million thanks Larry. It is working so fine, better then I expected.

Thanks a lot again.
 
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