Intermittent Problem with Circuit Design. Asking for Assistance.

Didn't you want the opposite? Your circuit is non-inverting. Jim's is inverting (and simpler; no zener needed).

It happens. ;-)

...

D'oh!

Yes. I got it back-asswards: Here's an excerpt of the OP: " The kicker is that at -24VDC it needs to be converted to +5VCD, and at -12VCD, it needs to be at ground."

Yeah, looks OK to me, except of course, I have to futz around with everything:

Cheers! Rich

That doesn't look like any circuit anyone suggested to you. Where is the 12V pulse coming from exactly?

You need to watch pulling logic inputs negative. Since the application requires no gain, a simple level level shift with over/under-voltage protection is all that's needed: View in a fixed-width font such as Courier.

. . . . . +5V . | 74HCT14 . -12 --- [10k] -- 5 . | 20VZ | |\\ | . | ---|>|--||--+---| o--- | . | / 1N914 1N914 | |/ | . -24 -- | --- 0 . [100k] . | . --- . gnd . . . . .

Ohh, 5V BVebo. Ouch! ...wasn't considering reality. ;-)

Maybe the common base configuration is a good idea. Thanks.