Author Topic: IR sensor advice  (Read 2438 times)

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Offline cnh121Topic starter

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IR sensor advice
« on: April 16, 2007, 10:23:39 PM »
Hi, I searched for this but couldn't find anything.  I am looking some sort of motion detector that also reports distance to the moving target.  I am pretty good with SONAR, but I've only used IR for line following and distance sensing of around 20-30".  All of the IR sensors I came across are for detecting movement OR distance...not both.  My application is so that somebody could wave at the sensor from up to 15 ft away so that I can target them in terms of both direction and distance.  I don't care too much about precision, just range and size.   It would also help if the beam width was small...since I don't want to target any objects moving to the sides of the sensor.   The reason I am not using ultrasonic is because I don't want to detect any objects between the sensor and the target that are stationary.  Is this even feasible?

Thanks for any help.

As a side note:  If it is necessary for the target to transmit a signal to some sort of receiver in order to determine distance, that is acceptable.
« Last Edit: April 16, 2007, 10:27:31 PM by cnh121 »

Offline nanob0t

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Re: IR sensor advice
« Reply #1 on: April 17, 2007, 04:09:14 AM »
Well, if you want to detect humans, take a look at thermopile arrays:

http://www.robotshop.ca/home/products/robot-parts/sensors/thermal-array-sensors/index.html

They're quite expensive though.  An explaination:

They're a passive sensor that measures body heat radiation from a long distance.  The sensor is passive, which means if a human were to sit there perfectly still upon activating the sensor, it wouldn't pick them up.  If they moved, then it would pick them up.  This could encompass the part you said you wanted the human to be waving.  I'm not sure, but you could probably do something to measure distance.  It has a grid within the sensor that splits the IR upon sending, and I'm sure that would create an image of some sort that could be compared to get distance.  Either that, or you could make it have a separate fucntion after it detects someone to find distance.

Just a thought.

Offline cnh121Topic starter

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Re: IR sensor advice
« Reply #2 on: April 17, 2007, 03:13:28 PM »
Thanks for the reply, I had already looked at those sensors.  I am looking for something with about 15-25 ft range though. 

Offline nanob0t

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Re: IR sensor advice
« Reply #3 on: April 18, 2007, 11:15:42 AM »
Ah, that gets a lot more difficult to find, and requires lots of money in many cases.  Consider it and figure out if there is any way to work around it.  I'll look for something with that much of a range.  IR working at 15-25 feet gets more into IR rangefinding, and becomes quite pricy. 

Here is a rangefinding IR, but I don't think it has capabilities of detecting human specific objects.

http://www.acroname.com/robotics/parts/R48-IR12.html

Perhaps consider other options?

Offline Admin

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Re: IR sensor advice
« Reply #4 on: April 21, 2007, 07:06:31 PM »
To detect movement you need to 'record' two 'images' spaced over a period of time, then compare the differences between the 'images'.

For example, if your sharp IR reads 25 one second then 202 the next, obviously something moved. You also know the change in distance, and the absolute distance, too.

However you seem to want a wide angle sensor, at least in the 2D and maybe 3D? And then know exactly where the movement occured . . .

Have you considered combining multiple sensors? For example, 5 sharp IR next to each other?

Depending on accuracy, field of view, and quality you require, a camera might be the best option. Just a thought . . .

Offline cnh121Topic starter

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Re: IR sensor advice
« Reply #5 on: April 23, 2007, 02:09:57 PM »
The only problem with the Sharp sensors is that they don't reach the distance I'm looking for.  I don't have to have a wide angle sensor, using mutiple sensors is not something I am against.

Are there any IR sensors that detect the direction in terms of degrees at the distances I'm looking for?  If so, I could use triangulation to determine the distance. 

 


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