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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Help ID a keypad debouncing SMT bit
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. |
#2
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Help ID a keypad debouncing SMT bit
On Thu, 09 Oct 2008 19:37:48 -0500, Richard J Kinch
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. |
#3
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Help ID a keypad debouncing SMT bit
On Fri, 10 Oct 2008 13:28:46 +1100, Franc Zabkar
put finger to keyboard and composed: On Thu, 09 Oct 2008 19:37:48 -0500, Richard J Kinch 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. |
#4
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Help ID a keypad debouncing SMT bit
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. |
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