What low-cost sensor detects objects moving between 10kph and 170kph at a 2m range?

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Hello fellow humans,

Excuse the simplicity of this question. What I'm looking for is ancient technology, but I have a lot of learning to catch up on. Based on the following details, could you please suggest what sensor (model number preferably) I'm looking for?

1. Detect movement of one of the following 'Objects': 1) " diameter by 1" high hard black rubber 'disk' (speed: 20-170kph), 2) person running by the sensor (assume feet are always on the ground) (5-30kph), and 3) the swipe of a hand (not sure the speed of a typical hand swipe).
2. Movement simply means presence of one of the objects in front of the sensor. If you know of a sensor that can detect speed as well that would be interesting, but not necessary.
3. It's preferred that the sensor doesn't require a reflector or a 2-part system, but it's not out of the question if that's the best option for cost and reliability.
4. The device that the sensors will be used in is the shape of an Apple TV box. The idea is to put sensors on the 4 sides, for detection of all 3 Objects, and one on the top, only for the hand swipe.
5. Use in dark or light environments is preferred, but if only one is an option, then it would be light environments (gym lighting or daylight).
6. The temperature range of the Objects is -20 to 40 degrees.
7. The sensor detection range should be a minimum of 2 meters for the 4 side sensors. Up to 3m is fine, but not necessary. The top sensor, which is just used for the hand swipe could be 1m, if that means using a cheaper sensor.
8. Within 0.2 seconds reaction time is ideal.

Minimum Application:

Detect the presence of an Object when it crosses a plane. Reliability is paramount.

Note:

A normal cheap IR sensor that we tried barely senses 50cm, so that's why I'm looking for a specific model number, if you're aware of something.

If I missed any detail, please let me know! I will happily get into a deeper discussion. Thank you in advance for sharing your knowledge.

Wish you a happy and peaceful day.
 

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For example;
Golf balls can be sensed with a vertical array of interruption IR paths for velocity and height. But for reflection this is a much smaller signal especially if black..
Not all black objects are black with IR so reflectivity must be given. as a % of white and the wavelength used. Black paint has a high coefficient (looks grey) and Sharpie black Ink is very low. Rubber may also be low and is diffused.

So a reflection coefficient test is needed with typical IR LED and/or laser wavelengths., if you can.

170 kph is ~ 47 m/s or 47 mm /ms at zero range but if at a 2m range and a semi circle of 6.28m detection of the object signal is now reduced and is inverse to R^2. This can only be made more linear with a pulsed Laser emitter and very small horizontal viewing angle but a wide vertical detector using AGC to detect small changes.

A 3D sketch of all objects and detection window, as height, distance and viewing angle are all important but sounds like a hockey puck goal sensor.

Waiting for your answers.
 

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    fuee

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I'm reminded of equipment that either:

1) detects how fast a pitcher throws a baseball, or
2) radar gun that police use to detect vehicle speeds, or
3) portable cameras turn to follow a subject moving, or
4) porch-mount security cameras detect and focus on subject in field of view.
 

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Hi,

what I miss is: the specification of accuracy and where the sensors are located.

I mean, if the sensors are besides the travel path ... you probably get some speed accuracy error.
But if a doppler radar sensor in exactly "in path" ... the sensor would be hit with your 170kph rubber disc. ... and maybe destroyed.

A sketch with travel path range and angular range and also where the sensors can be located ... would be helpful.
Sizes at all. Are we talking about an indoor living room applicatioin or is it some outdoor application on a football field size.

Klaus
 

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    fuee

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Thanks, so much for sharing your thoughts, Tony. You're right. It's a hockey puck. Black hard rubber. Can forget about velocity for now as that complicates things and is a plus, but not a necessity. When the puck crosses a plane, like a goal line, the sensor recognizes it. In this application location relative to the goal line doesn't need to be accurate, as long as the sensor knows the puck is there.

Also, if one kind of sensor isn't feasible to detect all 3 Objects, we can look at what works just for the puck.
 

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Klaus, thank you for the insightful questions. Imagine the disk (which is an ice hockey puck) going across a goal like. Use environment is an ice rink, gym, driveway, garage, or a location where people can shoot on a goal. When the puck passes the detection window of the sensor, which can be just a line, don't need a wide angle, the sensor is triggered.

Does this help?
 

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Hi Brad, these all make sense. Thanks for sharing your thoughts. I'll respond on each one to help define the objective.

1) detects how fast a pitcher throws a baseball, or
- Our primary use case is simply to determine presence of the Object, speed is secondary and not necessary, just an option.
2) radar gun that police use to detect vehicle speeds, or
- These, like a good radar gun, are high cost. We'd like something that's cents, rather than dollars. If it costs dollars then we'd probably need to change the product design to include less sensors per device. Also the distance we're looking for is 2m, whereas the car radar probably works at over 10m.
3) portable cameras turn to follow a subject moving, or
- That's more software, power consumption, and performance than I expect we need. I'm looking for something really simple. Just to detect when a line is crossed.
4) porch-mount security cameras detect and focus on subject in field of view.
- The black disk (hockey puck) can travel up to 170kph. Reality is that we can probably get away with as low as half that though, since we're only sensing it when it's on the ground and usually when it's shot quickly it's a little off the ground.
 

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fuee said:
distance we're looking for is 2m, whereas the car radar probably works at over 10m.
Click to expand...
Every so often there's a discussion at Edaboard about making a room-sized radar system, either light-transmitted or audio-transmitted. (Often the plan is to mount it on a robot.) Since you wish to detect a moving object, spectral shift might assist. Moving away from your sensor, slightly red. Toward your sensor, slightly blue.

Astronomers use the same strategy. Suppose you watch through a color viewer, yet you adjust stationary objects to appear black or white or gray. Then the slightest color change is a moving object.
--- Updated ---

Put two identical sensors at a 90 degree angle just like one is on the X axis, and the other sensor is on the Y axis.
 

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Hi Brad, appreciate your continued interest. What I'm trying to achieve seems simpler than this. The goal is just to know when an Object crosses 1 axis. For example, knowing when runners cross the finish line of a race or when a hockey puck crosses a 2m line. Any ideas of the lowest cost sensor for this kind of thing? Ideally, one sensor is enough, but if a sender and a receiver is necessary, so be it.
 

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Unfortunately you could not answer my 2 requests.
A fundamental problem is goalie interference with optics at the goal line. Two corner cameras might be the only way with motion detection and pattern recognition.
 

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D.A.(Tony)Stewart said:
Unfortunately you could not answer my 2 requests.
A fundamental problem is goalie interference with optics at the goal line. Two corner cameras might be the only way with motion detection and pattern recognition.
Click to expand...
Hi Tony, apologies, I didn't pick up on the requests. In this case there is no goalie, so no interference. What is the second request?
 

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fuee said:
The goal is just to know when an Object crosses 1 axis.
Click to expand...
I pictured boots in the background, a mixture of black & white pixels. It's starting to seem like an overhead view is sufficient. Is the background white ice? Have a camera shoot one picture per 1/100 sec. During the next 1/100 sec count black pixels.

a) If the tally is different, then you detected movement.

b) Or if the location of black pixels changed since the previous picture, then that detects movement.

c) Or if a group of black pixels follows a straight line compared to two previous images, then that detects movement.
 

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so .. you don´t want to measure the speed ... you are just interesteed in the "position".
I have to admit, since your headline talks about "moving" and "speed" ... I was focussed on speed measurement.
Now I see I was wrong.

Still a sketch with some dimensions would be helpful. It is way more informative and "international" than text.

Klaus
 

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First time that you come up with quantitative specs. There are however some wrong assumptions and specs are still partly vague.

You should clarify if you need distance discrimination. If so, the sensor choice is narrowing to ultrasonic, RF or light TOF or RF FMCW principles.

There are chip level IR light TOF distance sensors available, e.g. from ST. Also ultrasonic TOF is an option for cheaper solutions.
 

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Hey Brad! Within the 2m range there won't be any interference. No need to take that into consideration. These aren't used in a real game, but in a controlled environment.

Maybe the easiest example is a garage door or elevator door sensor that triggers when someone passes by. The differences here being Object size and speed. Plus, the puck and the running (or skating) is always flush on the ground if that helps. The Hand swipes are mid-air.

There's a lot of cool stuff we can do with cameras (speed of Objects, distance, etc). I assume the on-board firmware requirements are more extensive than a simple on/off sensor that detects the presence of an object. Ultimately the goal is to detect an Object's presence. Using the path with lowest development requirements and lowest cost is what I'm going for.

Based on that approach, my inclination is that IR, LiDAR, or some light/break sensor would do the trick, like @FvM has mentioned, but I'm not an engineer. Will respond to his comment with the results of recent component tests.
--- Updated ---

Hi Klaus, glad you mentioned this. Speed was included in the headline to indicate the speed of Object for detection purposes, not that a speed reading was necessary. Apologies for the confusion caused by that and thanks for your attention!!

I've attached a generic image I found on google that shows a similar use case.
NOTE:
1. That in my use case the Object is NOT transparent, like in the image.
2. The Objects in the image appear very close to the sensor. In my use case they can be up to 2m away. We can accept 1.5m if 2m isn't feasible, but I believe it shouldn't be an issue with the right sensor.
3. We would like to do this without a 'receiver' component, but can accept that if it improves reliability or lowers cost significantly.
 

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The best fit I see is a reflective mirror to a narrow beam LED or laser diode to an optical amplifier with adequate BW to detect.
Keeping the puck on the ground makes this possible.
A standard ice hockey puck has a diameter of 3 inches (76.2 mm). It is also 1 inch (25.4 mm) thick

170 kph or 47 mm/ms means a light path will be blocked at least 1ms depending on the optical aperture size and in this case the accuracy of the mirror reflector.

I would use a visible red laser diode and use a reflective surface that is rigid and can not be hit out of alignment like a garage door sensor. Using a diffused 5 to 10 mm aperture to detect the reflection offset from the emitter requires an accurate stable alignment of the mirror surface but it must be located at the goal's horizontal edge.

This is why I asked for a detailed sketch.
 

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Heya FvM! We're thinking in the same direction.

No distance discrimination is needed. Just knowing that an Object passed in front of the sensor within a 2m range is enough.

We tested with a standard low-cost PIR (not sure the model number). The reading time was ideal, but the range didn't exceed 50cm reliably, and that was with a reflector. We tried with ST ToF sensor VL5310. This worked reliably for hand swipe, but not as well for the fast-moving puck.
 

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There is a need to define the goal frame and sensor location by you and the reflection coefficient of the puck for IR. The TOF IR demands much smaller beamwidth than those on the market which then limits the range proportionally. So I doubt it would be useful.

For a reflection of 2m you have a range of 4 m and to detect a 50 mm blockage of reflected light must also prevent stray reflection of all objects other than the puck. This implies a very small beam width for the pass and stop band of tan^-1 ( 50 mm / 2000 mm).

I have detected objects before across a 1m aisle the size of a 1/4W resistor wire at slow speeds but this was using high speed unique codes transmitted on recessed sequential emitters with an array of detectors on the other side. But not at high speed.

Until you give an accurate model, this cannot be solved.
 
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Absolutely, Tony. Hopefully the image I used above helps with visualization. Note that the actual application of the sensor will be random places on the ice. Here are specific use cases.

Application 1: Two players are practicing passing the puck to each other. They want to see how many times they can pass back and forth within 30 seconds. Put the sensors between them and each time the puck passes it, a pass is registered.

Application 2: Make a racecourse. The side sensors trigger when the player skates by. With skating (ice or roller), unlike running, there's always one foot on the ground.

There are other applications, but all of a similar nature.
 
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For puck speed, 170kph is excessive. An upper limit of 100kph is all that's necessary.
 

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