latch circuit

[GLM590620]

I'm looking for a latch IC or a sutable circuit for use with a 4X4 keypad,
something that will keep only one key on untill another one is pressed.

Thanks

Gavin

 

[John Fields]

On 30 Sep 2003 22:00:13 GMT, glm590620@aol.com (GLM590620) wrote:

I'm looking for a latch IC or a sutable circuit for use with a 4X4 keypad,
something that will keep only one key on untill another one is pressed.
---

I'm not sure I understand what you're asking for , but it sounds like
what you want is something like this:

Let's say you have a 4X4 keypad and 16 relays, and when you press key #1
relay #1 comes on and stays on until you press another key. When you
do, relay #1 will drop out and the relay corresponding to the new key
you pressed will come on and stay on until you press another key, and so
on...

Is that what you want?

--
John Fields

 

[R. Steve Walz]

GLM590620 wrote:

I'm looking for a latch IC or a sutable circuit for use with a 4X4 keypad,
something that will keep only one key on untill another one is pressed.

Thanks

Gavin
----------------------------

Simple, 16 buttons to ground, each other pole with a guide diode toward
each button. Then pull-ups on the data lines, and pull them down as
needed by wiring the right button to the right bits to encode it in
binary.

Also bring together diodes from each button to one pullup, which
becomes the latch strobe, then use that to latch the value to a
latch, like a 74xx574 or such.

To do two digits, simply debounce the strobe and run it to a 74747
as a divide by two counter, that changes states to enable whichever
of the two digits, back and forth.

You COULD do some clock-driven polled circuit, but this is more elegant
actually. Run the latch outputs to two 7447's and two 7-segment LED
digits.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public

 

[Dana Raymond]

This chip will do the job for you. Its a 4X4 keyboard encoder with
self-latching output. Available at digikey.

http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=261&M=MM74C922N

Hope this helps
Dana Frank Raymond

"GLM590620" <glm590620@aol.com> wrote in message
news:20030930180013.28329.00000083@mb-m12.aol.com...

I'm looking for a latch IC or a sutable circuit for use with a 4X4 keypad,
something that will keep only one key on untill another one is pressed.

Thanks

Gavin