>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.

Make sure that the interrupt line is shielded and is not routed near any AC lines.  The interrupt line should be terminated at its source and not allowed to float.

>
>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.
>
I have had good luck using COMMON MODE EMI INDUCTORS on the line input with a cap across the input to the step down transformer.  Try TRIAD "E-CORE" inductors, DIGIKEY p/n 10523 to 10541 (page 254 of the current catalog) or PANASONIC Line Filters (Page 269 of the current DIGIKEY catalog).  BG Micro ( http:/www.bgmicro.com  had some at a good price ($0.99 ea.) on page 18 of their current catalog.

Good Luck, there are those amoung us that make a very good living solving these kinds of problems.

cheers,
Phil

Philip Starbuck
(909) 792-7917

"There are three principal ways to lose money.  Wine, women, and engineers.  While the first two are more pleasant the third is by far the more certain."
                                                -- Baron Rothschild
                                                        ca. 1860