Paul,

Did you guys consider using one of these,

<http://media.digikey.com/pdf/Data%20Sheets/Honeywell%20Sensing%20&%20Control%20PDFs/HOA698X-HOA699X.pdf>

rather than building the optical interrupt circuit from scratch? You can get this from Digikey for about $12.

<http://search.digikey.com/scripts/dksearch/dksus.dll?Detail&name=480-1946-ND>

You might find one in an old floppy drive.

Troy Ammons

That will work in some systems but the slot is not wide enough.
I need a 1/4 inch slot. I also used what I have been using
for the past 40 years as they have a glass lens with a very
narrow beam. Therefor they can be mounted further apart.

Paul Lamar