Line sensor

I am about to build a line sensor for a robot.
It should be able to follow a black line on a surface with different shades
of gray.
It would be good if the distance from the sensor to the surface could be 2 inches or more, but it is not a must. But redundancy to ambient light is important.
Could anyone please point me in directions of a stable solution?
/Tom
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On Sat, 29 Oct 2005 20:36:11 +0200, "Tom"

One possibility: http://www.jrobot.net/Projects/AVRcam.html
I haven't tried it, but it's on my to-do list.
--
Rich Webb Norfolk, VA

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If vision is a possiblility then check out this online tutorial on one way to use vision in a mobile robot to follow a line:
http://www.roborealm.com/tutorial/line_following/slide010.php
Works well for all sorts of lines ... even broken ones!
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RoboRealm wrote:

Excellent tutorial.
Mitch
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Thanks for the inputs.
I can see that some type of camera based system would be a good approach.
But the programming gets a bit complex, so I was planning for a solution with LEDs and photo transistors.
Any suggestions on a stable system build that way?
/Tom
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Tom wrote:

Have you looked at the Hamamatsu P5587 chip? They're about $2 US, and need some resistors and capacitors, but they reliably detect white vs dark stripes within an inch of range.
Check out
http://www.acroname.com/robotics/parts/R64-P5587.html
--
Mike Ross

Instructions said Win98 or better, so I used Linux.
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Tom wrote:

You could try tweaking this tho' the aim was a few millimetres from the surface for best results.... www.minisumo.org.uk/EdgeDetection.html
placin a few of these side by side you should be able to detect where your line is in relation to the sensors.
Best regards, colin
www.minisumo.org.uk/forum - a new forum for minisumo in the UK
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The line could be painted with a magnetic medium such as copier toner in pva glue; as well as being optically reflective. Just another idea.

The light source should be modulated at a particular frequency so that only the sensor will detect it; therefore other flashes of light reflecting off the surface will go undetected. This technique has been used extensively for T.V. remotes where the distance has to be several metres between source and detector! Cheap plastic lenses are available from electronics suppliers to focus the target onto the detector better and are filtered to mainly allow Infra-red light through. This technique has been used for security door break detector beams.

Use the above tried and tested methods and go searching on the Web for the best offers.

It`s a basic building block. Through practical use you will discover its pitfalls.

The pattern in which they are placed could be considered carefully to reduce components and circuit complexity. Another thought is that only one sensor is utilised and a moving lens or mirror scans the line.

----------------------------------------------------------------------- Ashley Clarke -------------------------------------------------------
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