I wouldn't waste the money on a one-shot in hte design, but like Steve suggested you could hook one up to your prototype to see if that addresses the problem. Its often faster to use such techniques to isolate the problem but not necessarily to fix it.

You can debounce the rotary switch, change the polling rate etc. Code fixes cost only time and braincells.

Since you have the A pin tied to INT0, I assume you are only using that when in sleep mode? Normally you poll? How regularly?

Do you have a tasker or timed interrupt to poll the inputs at regular intervals or are you using C programming loops? How fast is the microprocessor running?

I'd need to know more about the operation to determine if the problems are due to signal bounce or inadequate polling.

I'll look over the C code but assembly language is my forte in microprocessor applications.

-Jay C. Box