[ebarker]

Someone, Von Neumann I think, said that "hardware and software are equivalent"

I like the processor approach for this low quantity type project.

You should fire off a second timer/counter to measure elapsed time. It can periodically increment a timer variable.

Every time you get a pulse in you clear the timer. If say 50ms goes by without a start pulse, then you will know that because the timer variable is increasing. Then you can take your synthetic pwm output to zero, neutral.

So all together here you have 2 timers, to make things safe.

Ed