thanks for the input people, i really appreciate it.

I am going to try printing them on another printer first. The other one i have is a Xerox which has the ability to 'pile on' the toner and make it really thick. The other hp laser i have is a little on the pathetic 'economy' side.

The awkward thing is, the data sheet does not really give specifics on the working area of the sensor, only where the optical center of it is. i.e it does not tell me the minimum width over the optical center to sufficiently break the beam.

I think i should be able to get it to work without any extra electrics or de-bouncing but it might take a bit more trial and error. I don't think its a debouncing issue as it does not bounce when i break the beam with something random - even a piece of torn off paper seems to be fine... It mush just be my dodgy disks.