Hoping this is the right place for this. Honestly not even sure what to call it. Essentially I need to find a way to detect an object flying through a physical portal/gateway/doorway. I do not care where the object goes through or direction just that it did. I'm looking to detect ping-pong ball.
You can generate a line with a laser using optics. You can focus that line on an array of photodetectors, and detect when the golf-ball-sized object breaks the plane. There are many variants of that idea. The geometry and opticsmight get a bit complicated to cover your whole space.
There are many variations. For example, Instead of a line laser, you could use splitters and mirrors to create a span of parallel rays fine enough to detect your object.
You could use a series of infra-red LED's and IR phototransistors. Industrial processes already use this idea, known as a Light Curtain. Use the dark or opaque kind of LEDs and photo-transistors, as they will be less sensitive to visible light. Place an LED pointing across the opening at a matched photo transistor. Use a lens or piece of drinking straw to make each beam more-or-less linear. Use many of these across the opening (half the width of the ball apart or less.) Repeat on the other axis if you need X/Y coordinates. (Much more work...)
Then energize all of the LED's. This can be achieved with simple constant-current source(s). Then it's just a matter of sampling or detecting changes in each phototransistor's output. It could be done with discrete analog circuitry such as op-amps, however the more practical solution today would probably be a large microcontroller with many analog-to-digital inputs. Sample each sensor very quickly, and compare this value with the last value (or an average value.) If the difference is more than some threshold, sound an alarm.
I was first inclined to say "impossible", but I can think of a possible solution. It's going to involve a lot of learning and probably a few tries to get it right. You could use some high speed cameras (maybe these: https://www.ptgrey.com/grasshopper3-23-mp-mono-usb3-vision-sony-pregius-imx174-camera). They run up to 162 frames per second, so if your ball is moving at 10m/s, that's 6.2 cm per frame. If you can mount the cameras such that their field of vision is at least 3 times that (19 cm), you could conceivably get this working. You would probably want a clear border 20cm around the edges of the doorframe so that the ball cannot come too close to the cameras, otherwise they could miss it. Maybe 1 camera would be sufficient; it depends on the geometry of the opening. This is sounding very expensive, especially considering the computer(s) that would be connected to the cameras.
If you can tolerate a very big, long doorway with a comparatively narrow opening, you could make this project much easier by using lower speed cameras. It might be more appropriate to call it a "tunnel" at that point though.
Caution. This is an 'R&D' answer.
Figure 1. Laser printer scanner. Credit: Jeroen74 - Wikipedia.
The rotating prism sweeps the laser beam across the lens in a repeating pattern. If you can intercept the returning wave you may be able to detect presence or absence of an object. You may need a split-prism or half-silvered mirror to split the transmitted and returning beam.
- Mount the scanner overhead looking down on the centreline of the table.
- Run prismatic reflective tape around the frame so that laser light will normally get reflected back.
- Monitor reflected light level. Trigger when beam is broken.
This is complex but could be a super project.
Take laser safety seriously. Eye damage is permanent. I have no idea what power levels are used in these devices. If it is unsafe you could use the mechanism and a separate laser. Search for 'DIY laser scanner'.