>The only extra part I might consider would be 20us
>monostable, like a 555, 74123 or 1/2 a 4001. This
>could also be made variable so that the 20us is not
>dependent on s/w, leaving you with only the
>frequency to worry about

It would also provide a failsafe in case the micro locks up leaving the
drive to the LED on. The hardware timer will ensure the led is not left with
permanent high current drive, resulting in failure of the LED.

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