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Richard J Kinch
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 Posted: Fri Oct 10, 2008 5:37 am Post subject: Help ID a keypad debouncing SMT bit |
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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. |
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Franc Zabkar
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| Posted: Fri Oct 10, 2008 7:28 am Post subject: Re: Help ID a keypad debouncing SMT bit |
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On Thu, 09 Oct 2008 19:37:48 -0500, Richard J Kinch
<kinch@truetex.com> put finger to keyboard and composed:
[quote]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.
[/quote]
Diode array? (A)node/(K)athode?
- Franc Zabkar
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Please remove one 'i' from my address when replying by email. |
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Franc Zabkar
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| Posted: Fri Oct 10, 2008 7:48 am Post subject: Re: Help ID a keypad debouncing SMT bit |
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On Fri, 10 Oct 2008 13:28:46 +1100, Franc Zabkar
<fzabkar@iinternode.on.net> put finger to keyboard and composed:
[quote]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?
[/quote]
Maybe the DAx parts are wired as follows:
IN1 >----+-----> to uP
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o
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+Vcc |--|<|--+--|<|--| Gnd
o---| |---o
K |--|<|--+--|<|--| A
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o
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IN2 >----+-----> to uP
This kind of setup is often used for ESD/latchup protection.
- Franc Zabkar
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Please remove one 'i' from my address when replying by email. |
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Richard J Kinch
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| Posted: Sat Oct 11, 2008 6:48 am Post subject: Re: Help ID a keypad debouncing SMT bit |
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Franc Zabkar writes:
[quote]Diode array? (A)node/(K)athode?
[/quote]
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. |
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