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View Full Version : expanding pins I/O with a 4099BE ?



mobile_bob
08-04-2008, 01:39 PM
has anyone had any experience using this chip for the purposes of expansion of a bs2's I/O?

i have an I/O board that uses two of these chips to address two banks of 8 output ssr's

i would like to hear if anyone else has used this chip, and maybe what the outcome was
any special concerns, maybe a circuit example

thanks

bob g

mobile_bob
08-05-2008, 12:52 AM
no one?

i was hoping that someone here would have run across its use at least.

bob g

Mike Green
08-05-2008, 01:10 AM
It's not a very good general purpose output expander if only for the very limited output current (less than 1mA). The CD4xxx series parts were not made for driving any significant current load. You'd do much better with the 74HCxxx series (like the 74HC595)..

mobile_bob
08-05-2008, 07:38 AM
Mike:

thanks for pointing that out!

that would explain its use on this board where it is used to drive a 4049 hex inverter chip, which in turn drives the ssr's.

they might use this low value component as a failsafe, to burn out and not allow somesort of backfeed to be send back the the

cpu i suppose.

i guess i gotta learn to read the spec sheets more closely, huh?

thanks

bob g

Mike Green
08-05-2008, 07:52 AM
You really can't use either the 4049 or the 4099 as a "fail safe" since they're not designed to fail safely. Don't ever count on something like that. The SSR provides the protection along with the basic design of the board itself (like separating logic and power signals, shielding one from the other, adequate bypassing of the logic supplies, etc.).

Yes, do read the datasheets. That's what I do. They're readily available via the internet.