Joe:
There are 3 basic types of photo-eyes on the market. Through beam, retro-reflective, and diffuse. You always need an emitter and a receiver. Through beam requires two seperate sensors (a seperate emitter and receiver.) Retro-reflective and diffuse have both emitter and receiver onboard the same sensor, the difference is how the reflection or lack of reflection is handled internal to the sensor.
The reason I point this out, is that all sensors are not created equal. You might find that a different type has better accuracy and less bounce without changing anything other than that.
NJ wirenut is right on the money. I would add a redundancy with a second sensor to make an AND gate....i.e. both have to be on.
As far as timers go. Once you add up the amount for timers and the like. A micro-plc might be just as cost effective. Cost's have came down quite a lot over the last few years.
IMHO,
Carl
