I'm working in a project that count the number of packages out of a production unit..
I have read a lot of articles that explain 2 kind of sensors :
1- IR Emitter - Receiver .
2- Laser Diode - Photocell.
I need the most accurate and executive solution that takes the following into consideration :
Thank you very much and sorry for my bad English >_<..
YOu need to tell a lot more before any serious advice can be given.
e.g size of the packets, LxWxH or odd shaped with holes?
speed of transport
distance between packets
reflectiveness of packets
content of packets (?)
etc.
These all will influence the choice for certain system.
Thank you robtillaart for your reply..
It's an interlock/bricks/tiles plant, every packet is a 1 meter^3 of packed palletized bricks/tiles or other cement products,
the speed is slow, a bout 15-20 packets every minute, and the distance between 2 packets is 50cm...
The dust part makes using light sensing require regular cleaning, and the non-conductive nature of the objects cuts out EM sensors that I know. I'm not even sure that the dust would spoil ultrasonic detection.
Can you pick up on the weight born by whatever conveyor you're using?
More foolproof would be wooden fingers hanging on hinges from above. A block would have to make several lift at once. You could put magnets in those and detect movement with cheap, dependable long-life no-internal-moving-parts-to-wear security Hall switches -- same kind you'd put on windows and doors.
50 cm... that's about a cubit isn't it?
30 meter/minute with 30-40 change signals per minute.
HW: laser with sensor:
SW: attachinterrupt() with an internal debounce timer of 0.2 sec should do it.
real problem is to keep sensor clean enough
magnets as goForSmoke said is indeed better I think
I also avoid mechanical switches as I wear them out in mice so often.
I forgot... maybe there'd be some way to use capacitive sensing?
belalsaleh:
Thank you robtillaart for your reply..It's an interlock/bricks/tiles plant, every packet is a 1 meter^3 of packed palletized bricks/tiles or other cement products,
the speed is slow, a bout 15-20 packets every minute, and the distance between 2 packets is 50cm...
Seems that a simple "finger" switch, hall sensor, or ultrasonic sensor would work well. I would probably implement all three as each are so cheap and it would allow for a fail-safe system (2 of 3 would trigger a count and less than 3 would trigger an alarm of a possible sensor failure).
I'd be willing to accept your flight arrangements to fly to your location and implement this system if you need help 
Tim
robtillaart:
30 meter/minute with 30-40 change signals per minute.
Run checks fast enough that you can debounce like you would a button. If a finger swings after the block passes under it, you want that debounced. 100 checks per meter of travel is a lot harder to false than 1 or a few. Unless of course the debounce is done in hardware, which costs more.