Doppler Effect Sensor Ignoring Wind

Hello friends, I am working on a project to detect when a basketball shot is attempted on an outdoor court by using a device clipped onto the bottom of the net. I am determined to stick with a device on the bottom of the net. I found a great sensor that almost allowed me to accomplish this called the x-band motion sensor from Paralax which uses the Doppler effect to detect motion so that even if the ball doesn't hit the next it would detect the shot. Things seemed to be working great until on a windy day my sensor kept triggering false positives due to the wind.

Does anyone have any ideas on if there is a similar type of motion sensor but that will only trigger if a solid object is causing the motion?

post a link to your sensor. do you think you can adjust the code to work with solid objects?

first thing that comes to mind is debounce. testing if it is really a value or if it is stray.

I doubt that an x band sensor can detect a basketball. It’s probably triggering on the hoop vibrations.

I have some of these units as motion detectors in a home sentry system. (I bought the raw radar transceiver and designed the amplifier/square wave generator, but the Parallax unit should give nearly the same results.) They are very sensitive, and should easily detect a basketball moving toward or away from them. Remember that a Doppler unit detects relative motion. Therefore, if the unit itself is not stationary, it's going to generate an output.

If you have attached this to the bottom of the actual net, won't it move when the wind blows? Your best position for this, I think, given the many angles at which the ball can approach, would be top center of the backboard, angled down by some amount. You aint going to win with this unless its mount is maximally stationary.

And as for detection, remember that the faster something is approaching (or moving away), the more square waves per second it generates. So a ball is moving pretty fast, like maybe 5 mph or more (just a guess), which should generate frequencies say in the 50 - 150 Hz. range. I set mine up so the square waves trigger an interrupt, which just counts incoming square waves. If you then set up a timer to start the count over, say every half second, you can look for enough square waves to be sure that your reading isn't ambient noise. Just an approximation, but each mph of closing/opening motion (i.e., directly at/away from the detector), will deliver about 10Hz.

I set mine up to ignore less than 0.5 mph (related to people walking), and it has yet to ever false alarm.

Thank you for the feedback all. Here is the link to the motion detector:

Aarg - it does see the basketball, When I test in my home without a hoop it triggers successfully when the basketball is the only thing I throw above the sensor. It is really an amazing sensor but I'm not having any luck getting it to work with high accuracy on an outdoor basketball court while hanging on to the bottom of a net.

I am thinking that based on jrdoner's comments I may have to accept that the only way I could pull this off from the bottom of the net is by using a camera or something. My goal is I'd like the average person to be able to go to their neighborhood outdoor park and then easily use this device, so putting something above the backboard seems a bit out of scope. I'll have to continue to ponder on this. finding the right sensor for detecting a miss seems to be the key to this project of mine. Infrared would have worked great if balls had heat in them.

that has a too large range - 8-30ft. Since it is hanging on the net, and wind moves it, it will see "the world" moving, or all its solid fixed objects within range as moving. I doubt it senses the air movement.

Use a lower range sensor, like a led proximity sensor with a couple inches range.

I'd mount the sensor near the net, at a fixed position. Then we can hope that the net, moved by wind, is not detected. Birds or bees still may be detected when flowing by.

first off, you say that you have tested it successfully. that means that you have passed the main problems.

1) location

2) installation.

now, you are trying to fine to 'operation'

if it is hanging on a net, looking at the sky, what are the x-band waves reflecting from ?

I would offer that if you set up a video and a data logger, you could watch the action on the court and at the same time watch the output of the sensor. then, from the comfort of your living room, watching the two data streams (video and stored data) you can figure out what you can do to adjust the sensitivity.

as a note, there is a space at the backboard, where the hoop attaches, that is a place the ball cannot touch. since the ball is round, and the connect of at an angle, you could place it there and then only see movement of anything above the hoop.