Help ID a keypad debouncing SMT bit

[Richard J Kinch]

I'm trying to identify an SMD on a PC board with some SPST keypad switches.
It has 4 terminals and is marked M1I. Each is labeled DA1, DA2, etc. on
the silkscreen, and two of the four terminals are marked A and K. All four
terminals connect off in different destinations. I'm guessing this is some
sort of debouncer or logic-level-shifter? But I'd like to know, if anyone
has any suggestions.

 

[Franc Zabkar]

On Thu, 09 Oct 2008 19:37:48 -0500, Richard J Kinch
<kinch@truetex.com> put finger to keyboard and composed:

I'm trying to identify an SMD on a PC board with some SPST keypad switches.
It has 4 terminals and is marked M1I. Each is labeled DA1, DA2, etc. on
the silkscreen, and two of the four terminals are marked A and K. All four
terminals connect off in different destinations. I'm guessing this is some
sort of debouncer or logic-level-shifter? But I'd like to know, if anyone
has any suggestions.

Diode array? (A)node/(K)athode?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[Franc Zabkar]

On Fri, 10 Oct 2008 13:28:46 +1100, Franc Zabkar
<fzabkar@iinternode.on.net> put finger to keyboard and composed:

On Thu, 09 Oct 2008 19:37:48 -0500, Richard J Kinch
kinch@truetex.com> put finger to keyboard and composed:

I'm trying to identify an SMD on a PC board with some SPST keypad switches.
It has 4 terminals and is marked M1I. Each is labeled DA1, DA2, etc. on
the silkscreen, and two of the four terminals are marked A and K. All four
terminals connect off in different destinations. I'm guessing this is some
sort of debouncer or logic-level-shifter? But I'd like to know, if anyone
has any suggestions.

Diode array? (A)node/(K)athode?

Maybe the DAx parts are wired as follows:

IN1 >----+-----> to uP
|
o
|
+Vcc |--|<|--+--|<|--| Gnd
o---| |---o
K |--|<|--+--|<|--| A
|
o
|
IN2 >----+-----> to uP


This kind of setup is often used for ESD/latchup protection.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

 

[Richard J Kinch]

Franc Zabkar writes:

Diode array? (A)node/(K)athode?

Yes, good call, thank you. Each chip is two diodes, four leads total. It
explains all the resistance measurements being open circuit, as the
ohmmeter wasn't overcoming the forward voltage drop. Measuring with a
diode tester succeeds.

I think the diodes are either encoding matrix signaling, or perhaps the
pull up/down you mention.