Detect (25.8mm) Metal Ball Passing through a pipe.

I am designing a PIC16F based project which incolves detecting a metal ball-bearing passing through a pipe. The ball is about 26mm in diameter.

I have to design a system to detect the ball passing though a pipe.


Initially I intended to use IR Tx and TSOP (1738) to do so, but apparently - the TSOP has a noise filtering mechanism which just ignores the ball passing at the velocity of gravity.

I chose TSOP to avoid the interference from external light, as TSOP 1738 only observes IR at 38kHz.

What alternative do I have for such a high response time, and yet be secured from interference from external light?

Pulse you IR Tx on/off at 38 KHZ?
Frank

If the pipe is non-metallic, use an inductive or magnetic proximity sensor. You should be able to find one with the correct response time.

It is easy to solve it. Just a little metal detecting work to do. You can rent a metal detector.

If the pipe is non-metalic, use a reluctance sensor, it will produce a voltage pulse as the ball passes it. This MAY work on some types of metalic pipes as well.
If the pipe is transparent, use an IR LED (NOT a TSOP type of device) and pass the light through the pipe to an IR phototransistor. If the IR beam is broken it will register on the phototransistor.
If the pipe is non-metalic and not transparent, you could also try a capacitive pick-up from one side of the pipe to the other.
If the ball is magnetic, you can use a pick up coil. It will induce a current in it as it passes by.

Don't use a TSOP style detector, they rely on the IR beam being chopped at around 38KHz or 56KHz and require several cycles to adapt before producing an output. As the ball may drop very quickly through their beam, it's likely they will not have time to react. A constant beam from a normal IR LED falling on a phototransistor will have a very much faster response time.

Brian.