My project envolves using a PIC to control a stepper motor.  Also envolved
is a high speed drill, similar to a "dremol".  It seems the drill is
generating huge amounts of noise on the AC lines and is screwing up the
external interrupt line of the PIC as I am getting continous interrupts.
The interrupt line is being used to monitor for a relativly infrequent, but
quite fast transient, hence the use use of the irq line.

I have tried running the drill on a seperate ac breaker, have installed
snap-on chokes on the drill line, inserted an opto-isolator on the irq
input and it still screws up if the drill is running.  It would appear to
be strictly a problem with the noise on the power as the spurious irq's
still occur even if the irq source line is removed.

The power supply is a conventional step down transformer, bridge rectifier
and fixed voltage regulator. I have added lots of filter capacitors of
various small and large sizes to no avail. You can still see the noise from
the drill on the Vcc with a scope, its quite pronounced.

Any ideas on how to clean up the supply.

Thanks!

Bob Bullock