How can I measure whether a football passes through a hula hoop? The main challenge is the need for outdoor use, which presents difficulties due to the presence of ambient light (sunlight). It might be possible to install a sensor module on top of the hula hoop, which comprises a Class 1 laser emitter and a receiver. The emitter emits invisible laser pulses that bounce off any objects in the sensor's field of view, and the receiver detects the returning pulses. When a fast-moving object such as a football passes through the hoop, it will interrupt the laser beam, causing the sensor to detect the change in signal and register the event. I also explored the possibility of using infrared (IR) technology to detect the passage of a football through the hula hoop.
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Does that meet your requirement of cheap? – Solar Mike May 06 '23 at 09:09
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@SolarMike While it may not be the most affordable choice, there is of course a trade-off between accuracy and cost. While I am actively seeking more cost-effective alternatives, I have yet to find a suitable cheaper option that meets my requirements. – FPSX V May 06 '23 at 09:14
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This question is likely to be answered with opinions rather than facts and citations. It should be updated so it will lead to fact-based answers. Also requests for alternative sensor options is basically a shopping question. You should read the rules about what sort of questions might be seen as invalid for this site. [What types of questions should I avoid asking?](https://electronics.stackexchange.com/help/dont-ask) and [What topics can I ask about here?](https://electronics.stackexchange.com/help/on-topic). – Andy aka May 06 '23 at 09:51
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1"*The emitter emits invisible laser pulses that bounce off any objects in the sensor's field of view, and the receiver detects the returning pulses.*" The most reliable method for detection of a solid object is through-beam sensing. The receiver normally detects the transmitted light and **loss** of light (breaking of the beam) means an object is present. Detecting of "returning pulses" is much more difficult. – Transistor May 06 '23 at 11:45
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2I don't think this answer is opinion-based. Asking for possible solutions for a design problem is not mere "opinion". And it is not a shopping question, unless one specifically asks for specific parts or modules. Voting to reopen. – LorenzoDonati4Ukraine-OnStrike May 06 '23 at 20:24
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3BTW, there are lots of questions of this kind on EE.SE, asking for alternative possible solutions giving some constraints, and they were not closed. Just an example [here](https://electronics.stackexchange.com/questions/651393/detecting-stalled-ac-fan-in-high-temperature-system/651701). – LorenzoDonati4Ukraine-OnStrike May 06 '23 at 20:27
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@LorenzoDonatisupportUkraine we should stick with what the community has decided is on or off topic in the meta. We usually answer specific questions that are related to electronic design. Broad questions are not encouraged – Voltage Spike May 07 '23 at 16:03
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A stock LiDAR sensor from Pololu will do the trick. They are designed to deal with ambient light. Choose one that has a wide field of view and a fast sampling rate. They got exactly one - it’s a D-shaped black PCB module that uses OPT3101. Done. That was easy, right? :) – Kuba hasn't forgotten Monica May 07 '23 at 16:56
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There are DIY articles on the Internet for chronographs for measuring bullet and arrow velocity. Perhaps a subset of this technique can be used for the football sensor. – qrk May 07 '23 at 21:00
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@VoltageSpike So why the question I linked to wasn't closed? I don't think they are so different, except for the fact that in that case the OP was an high rep user and the problem was apparently related to some industrial context. – LorenzoDonati4Ukraine-OnStrike May 07 '23 at 21:15
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@VoltageSpike, BTW, I'm sure I have seen other questions here that had the same structure (alternative approaches for an applications) and weren't closed. The one I linked to is just the one I remembered off the top of my head. – LorenzoDonati4Ukraine-OnStrike May 07 '23 at 21:27
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@LorenzoDonatisupportUkraine there are questions on both sides of the aisle. There are some questions that should be closed that remain open and then there are some questions that should be open but got closed. The goal is to keep both of those to a minimum, but we're dealing with a bunch of humans here so we try to do our best – Voltage Spike May 08 '23 at 05:38
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@VoltageSpike Sorry if I wasn't clear, I didn't want to criticize you mods. What I was trying to say is that sometimes there are high rep users that are a bit too eager to close a question if they think a meaningful answer cannot be given, even if the facts prove them wrong. The site has always been about *electronic design* not simply *circuit design*, so exploring the alternatives (if the problem is stated reasonably clearly) I think is on-topic. – LorenzoDonati4Ukraine-OnStrike May 08 '23 at 11:46
2 Answers
If you aim for absolute cheapness and an electromechanical solution fits your bill you could use microswitches.
Mount some microswitches on the hula-hoop and connect their levers to very light and rigid plastic strips that go from the microswitch to the center of the hula-hoop. When the football pass through the hoop it will momentarily displace one or more strips, that in turn would act on their corresponding microswitch. The strips should be so light that the football is not impeded in its motion through the hoop, of course.
The number of strips depend on the relative size of the football wrt to the diameter of the hoop. Probably 4 or 5 will do. You may have to tinker a bit and think of a way to fasten the strips to the hula-hoop (the other end would be flapping around near the center of the hoop) and how to make them act on the switch.
All this requires a bit of mechanical thinking and skills, but probably is unbeatable from a cheapness POV. You could get 5 microswitches for a couple USD and the other materials could also be recycled or commonly available stuff (for the strips I can think of electrician's cable ties, for example; when fastened to the hoop the part you usually cut-off is fairly elastic; there are quite long ones that could fit your application).
Moreover sunlight won't interfere at all. And if you don't need a particularly professional job, you can easily waterproof it all (after you test the set-up) with generous application of silicone sealant (silastic) and/or hot-glue.
In addition, since you don't have delicate electronic components, you could use common silastic for hydraulic applications, which would corrode components in the long run due to the presence of acetic acid in its formulation. The only parts you should protect are the terminals of the microswitches, where you would solder the connection wires. That's easy to do with some heat shrinks.
It's not an elegant solution, and aesthetically would probably look not too good, but its dirty cheap, especially if you have the skills to build it up, otherwise you could spend a lot of time to get it right (YMMV).
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While this is one way of doing it, modern sensors are quite amazing and a wide FoV LiDAR will do this admirably (among other things). About as plug and play as you can get. – Kuba hasn't forgotten Monica May 07 '23 at 16:59
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@Kubahasn'tforgottenMonica I'm not up to date to newest technologies like LiDAR when it comes to actual implementations and parts (BTW if you can share a link, I'd appreciate it, I'm curious). Anyway, since the OP mentioned "cheap", "arduino" and "hula-hoop+football", those keywords screamed "hobby (or school) project" to me, so I went with the first most cheap-ass solution it came to my mind (remembering the days when I was a nerdy high-school student dabbling with electronics and salvaging any electronic component I could get my hands on!). :-) – LorenzoDonati4Ukraine-OnStrike May 07 '23 at 21:21
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An ultrasonic proximity detector and an Arduino might do the job for less than $10. https://www.makerguides.com/hc-sr04-arduino-tutorial/ – PStechPaul May 07 '23 at 21:45
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Thank you for the responses. @LorenzoDonatisupportUkraine If I understand it correctly, using micro switches it is possible to detect when the football touches the strip, and it does not require a push to activate? The sensitivity of the micro switch allows it to respond to even slight movements of the strip. Is that correct? – FPSX V May 08 '23 at 09:08
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@FPSXV Microwsitches are just extremely sensitive switches, so they are on/off. You didn't describe your application too well. If the only thing you want to detect is whether or not the ball went through without too much precision about the timing, the only thing that matters is that at least one of the strip (which must be hinged somehow to the hoop and must be able to press the switch when moved) activates the corresponding strip. ... – LorenzoDonati4Ukraine-OnStrike May 08 '23 at 11:27
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@FPSXV So the switch *does* require a push, but they are extremely sensitive, so they don't need much force. You have to solve the problem of how to make the strip end near the hoop to act on the switch. That's why I said you need some mechanical thinking to devise the right setup. – LorenzoDonati4Ukraine-OnStrike May 08 '23 at 11:27
For this application, I would use a Time-of-Flight (ToF) sensor. This kind of sensor does not require any reflector, enabling the entire system to be contained on one side of the hoop.
Integrated circuits exist that implement ToF sensing, with a I2C interface that is easy to communicate with a microcontroller (be it an Arduino or otherwise). They automatically compensate for ambient lighting and work outdoors. Typical resolution for the distance measurements are would be 1mm, and supporting sampling rates of 25-90 Hz.
One alternative would be VL53L5CX, which gives a 8x8 array of distances. It has a 45x45 degree square FOV (65 degree on diagonal). It could be mounted either looking straight across the hoop, or slightly up or down. The processing would be able to look at the distance to the ball, as well as the shape. Official break-out boards are available for 20 USD. Or 10 USD for the cheapest from China. The chip costs 7 USD @ 100 pcs, and 5.5 USD @ 10k. Other array alternatives could be TMF8820/TMF8821 with 4x4 and 30 Hz sample rate. It is as low as 4.5 USD @ 10k units.
It may also be possible to use a single-channel ToF distance sensor. Those are down to 2 USD @ 10k. But due to the more narrow FOV, the sensor would have to be further away and look up/down into the hoop. This might increase total system costs by more than the available savings. Reliability might also be lower due to the inability to look at the shape of the object.
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