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I have a simple 3 ft by 3 ft goal. I want to electronically detect when a ball passes into the goal but not when it goes wide.

I had initially thought i could use a simple PIR motion detector pointing downward on the cross bar but I am concerned that 1) it might detect balls that go wide? (how do i restrict the arc) 2) it might be too slow for a fast moving ball 3) it might miss balls in top corner etc

Option two is a series of emitter reciver ir pairs on each side of the goal post. Enough to make sure that a ball can't get through. See attached sketch of the options.

I have zero experience with this. I am thinking the emitter pairs is best option but I am unsure? Maybe there is another alternative? The overriding concern is that the solution must require minimal power to run (and cost!).

options

edit as directed by site to explain why not duplicate -- to reiterate my comment below: yes they are similar questions. I think my question was more specific. I asked specifically for option a) or option b) or something else. Steve G kindly informed me why the PIR was not suitable -- as it uses temperature -- as opposed to use solution this because i think so. For this reason I think this question is worthy as a standalone and I will update the answer to reflect why PIR was not suitable.

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    \$\begingroup\$ I'm not sure that a PIR will detect a football. A PIR detects a difference in temperature between a moving object and the background. That works well when the object is a person, who usually will be hotter than the background, but a football would be about the same temperature as the background. It is also quite small so doesn't give off a lot of IR radiation anyway. \$\endgroup\$ – Steve G Oct 29 '16 at 21:29
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    \$\begingroup\$ I just noticed that you said the goal was 3' x 3' so presumably the ball is smaller than a football. That makes it less likely that a PIR motion detector will work. I suggest you look at Goal Line Technology \$\endgroup\$ – Steve G Oct 29 '16 at 21:36
  • \$\begingroup\$ Hi @SteveG thanks for the replies. Yes it's 3ft by 3ft goal but i do intend using standard size 4/5 footballs to start. Based on you're 1st comment re: temperature this might be a moot point anyway and the emitter/receiver pairs look like best option. thanks again \$\endgroup\$ – user1843591 Oct 29 '16 at 21:51
  • \$\begingroup\$ hi @ChrisStratton, yes they are very similar. I think question was a bit more specific. option a) or option b) or something else. Steve G kindly informed me why the PIR was not suitable -- as it uses temperature -- as opposed to use this because i think so. For this reason I think this question is worthy as a standalone and I will update the answer to reflect why PIR was not suitable. I am open to discussion too etc as I am not fully au fait with procedure re: duplicates and so on. \$\endgroup\$ – user1843591 Nov 9 '16 at 14:44
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just to officially post an answer to this question, reposting what @SteveG said above in the comments, a transmitter receiver pair is the most suitable option.

A PIR is deemed unsuitable as it

detects a difference in temperature between a moving object and the background

and as such is unsuitable to detect an object that is likely to have a similar temperature to the ambient temperature

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