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Topic: What sensor should I use to detect object going through a hole? (Read 2 times) previous topic - next topic


I was thinking that maybe with the IR, the beam might not be broken if the washer went thru, say,  parallel to the ground or tilted on some plane that slides thru beam undetected.  Another sensor picking up a reflected signal when normally it receives nothing kinda acts like a NO switch.  The others being NC naturally.  Too complicated though, the LASER is simpler and more precise.  Though the extra precision from the narrow beam has its disadvantages too by making it harder to "cover" the hole.  I suppose a "real engineer" would come up with something that worked 99% and cost 9 cents to implement.  ;)

Again, the LASER (diode) has the advantage that, though it's not the cheapest part in the world, you only need one if plan your "route" carefully.  Mirrors are passive and tiny ones must surely be cheap in bulk.
Experience, it's what you get when you were expecting something else.


Here comes the 9 cent solution, well closer anyway.  Inductive pickup from hall sensor or something like a simple metal detector using coils of wire.  When money is no object, then use RFID.
Experience, it's what you get when you were expecting something else.


laser has the advantage that any object can be used for the game.
I could see reflectors being a little trickier to set up and keep maintained.
metal detector has the disadvantage of also detecting if the ring is just sitting above the coil and not actually going thru the hole.
So everything is a tradeoff.
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I may have been wrong with the sizes. The hole diameter may be 4". I'll have to confirm this.

RFID is a very interesting option. It would allow me to identify which player's washer went through, which would be great. But I would need to rule out washers sitting on top of the board (that did not go in the hole). And I would worry about the constant throwing and hitting of the board wrecking the RFID chip.


IR phototransistors are much more responsive (report light changes more quickly) than photocells. If you try to catch a washer free-falling through the hole with a photocell I guarantee you'll have problems -- even using a laser as a light source. Using a real world example I can say that you can pretty lazily drop your arm through the laser and the photocell won't give enough voltage swing for accurate detection.

The simplest solution would be to put a funnel under the hole so the washer ultimately drops through a restricted space. I'd still recommend using an IR phototransistor and a red LED. An IR LED is not required and makes things more difficult because you can't see it. The other advantage of phototransistors is that you can use them with digital inputs and won't have the problems with the Arduino ADC mux.

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