Author Topic: Motion Sensors  (Read 997 times)

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Offline Stuart HuntTopic starter

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Motion Sensors
« on: April 17, 2010, 08:36:13 AM »
Hi
I am a student at the University of Central Lancashire. In my current project I am developing what is essentially an 'intelligent' garden sprinkler toy for kids. However for the product to fully function as I wish, I need to find a sensor that can do the job I want doing. I was wondering if any of you guys could help?

Basically, what it needs to do is to sense motion in 360 degree's to a distance of around 5 - 8 meters, and then be able to feed back to the central PCB the information of where this motion is occuring, so that in turn the sprinkler system (which ive already managed to develop) can shoot water in that direction. The closest thing ive been able to find so far is car parking sensors.

The actual PCB information isn't so important, but a link to information about a possible sensor would be extremely helpful. Any ideas?

Thanks in advance, Stuart Hunt

Offline Razor Concepts

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Re: Motion Sensors
« Reply #1 on: April 17, 2010, 08:51:24 AM »
Sense movement or people?

If you want to sense people you can use a Passive Infrared Sensor (PIR).

You can shield those sensors to have a smaller viewing angle, and arrange them in a circle.

Offline Cristi_Neagu

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Re: Motion Sensors
« Reply #2 on: April 17, 2010, 08:59:07 AM »
Well, he's talking about sprinklers for kids. That means hot days. That means that most likely an infrared sensor won't be able to tell the difference between people and surrounding warm/hot objects.

Also, after you pour water on a kid, he won't register anymore as warm. Which will disrupt the readings of the sensor.

Good luck with your project.

Offline Soeren

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Re: Motion Sensors
« Reply #3 on: April 17, 2010, 11:36:09 AM »
Hi,

That means that most likely an infrared sensor won't be able to tell the difference between people and surrounding warm/hot objects.
PID sensors register movement of bodies with a temperature different from ambient perpendicular on their two windows, simple as that.
If the garden bench get hot and runs toward the sprinkler, perhaps it's because it needs a chill ;)


Also, after you pour water on a kid, he won't register anymore as warm. Which will disrupt the readings of the sensor.
That would require massive amounts of water and if the kid actually got colder than the surroundings (highly unlikely), a temperature difference would still exist.

PIR devices with Fresnel lenses can be had covering a narrow or a wide angle 90° to 120° is easy to get and would then require 3 or 4 for a full circle detection and assuming lots of kids running around, perhaps it would be more sensible to open the water valve (or increase pressure) on detection, rather than trying to control the direction of the water, as it would be quite expensive with eg. 10° zones (and hard to get btw.), and if kids come from every direction, then what?

If the ground around the water area is somewhat controlable, sensor wires could radiate out from the water gizmo - capacitive sensors might be hard to use, due to the ground effect, but piezo wire should be good (although quite expensive).


Another thing to consider is, that it need to be totally water proof - and don't include mains voltages or things may go really bad.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline Stuart HuntTopic starter

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Re: Motion Sensors
« Reply #4 on: April 19, 2010, 09:52:19 AM »
Hi,

That means that most likely an infrared sensor won't be able to tell the difference between people and surrounding warm/hot objects.
PID sensors register movement of bodies with a temperature different from ambient perpendicular on their two windows, simple as that.
If the garden bench get hot and runs toward the sprinkler, perhaps it's because it needs a chill ;)



Also, after you pour water on a kid, he won't register anymore as warm. Which will disrupt the readings of the sensor.
That would require massive amounts of water and if the kid actually got colder than the surroundings (highly unlikely), a temperature difference would still exist.

PIR devices with Fresnel lenses can be had covering a narrow or a wide angle 90° to 120° is easy to get and would then require 3 or 4 for a full circle detection and assuming lots of kids running around, perhaps it would be more sensible to open the water valve (or increase pressure) on detection, rather than trying to control the direction of the water, as it would be quite expensive with eg. 10° zones (and hard to get btw.), and if kids come from every direction, then what?

If the ground around the water area is somewhat controlable, sensor wires could radiate out from the water gizmo - capacitive sensors might be hard to use, due to the ground effect, but piezo wire should be good (although quite expensive).


Another thing to consider is, that it need to be totally water proof - and don't include mains voltages or things may go really bad.


Thanks guys! All extremely helpful! I'm pretty sure i'm going to go with the PID sensors. The current design of the product suits this best and with only a month and a half to deadline day im not really in a position to change everything round all of a sudden! I should have looked at the sensors a bit earlier in hindsight but ahh well.

Aye, the last bit is number one on my specification haha. All the electrical components are in sealed areas already and ive included a circuit breaker.

Thanks again! Ill pop back when its all done and show you all the finished jobby! Also, when I break up for summer this $50 robot looks quite fun!

 


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