Line Following Sensor

[rbtying]

Hey all,
     I've been asked to help on a project involving line-following with a clearance of 1" (between the sensor and the line).  I'd like any recommendations on sensors, or possible strategies.  I have a theoretically unlimited budget.  The line is about 2" wide, and reasonably reflective.  The system will be running on 5v logic, but I can probably pull power from the batteries to supply voltage less than 12v. 

Any help would be greatly appreciated.

[TrickyNekro]

The sensor would be a QRD1114 from fairchild...
Tested working... even with halogen lighting...

Do you want to build something or get something ready... Ready solutions, I don't know, maybe someone else...

But with QRD1114 things are pretty simple... You either use a Schmitt trigger circuit and feed back the data to an digital pin...
Or you can read QRD1114 outputs with a ADC and judge accordingly...

The ADC method is more flexible... But the Schmitt trigger method is easier to code...
Not that there would be huge differences... but just telling...

If you don't know the lighting conditions go with the ADC unless you really need that extra ADC pins for something else... but I believe you wouldn't...

Lately... I bought these... But haven't used them for anything so... it's your call...
They are cheaper than QRD1114 but I don't know of their performance... ;-)
http://gr.mouser.com/Search/ProductDetail.aspx?R=OPB609GUvirtualkey54210000virtualkey828-OPB609GU



Hope I helped...
Best Regards, Lefteris
Greece

[rbtying]

Does this sensor work from an inch or two away (2.5-3cm)?  That's the biggest requirement.  I will probably be using ADC, but the interface isn't that important.

[waltr]

I just looked at the data sheet for that sensor (OPB609) in the link above. From what I see in the graph of Output vs Distance this sensor will not work at even 2cm, Looks like the distance needs to less than 2mm.

For a distance of 2-3cm I would go with discrete LED and photo-transistor.  And even then a lens may be required on the photo-transistor but may not since the line is fairly wide. You may get away with just a tube to limit the detection angle of the photo-transistor.

You would need to experiment to determine the exact configuration.

[TrickyNekro]

Well... 3.5 cm is quite the distance.... Yup didn't see that... 1'' clearance...

Are you sure that this can't change?

I could come up with some other solutions, but you'd probably have problems spacing the sensors as the reception area would be wider...

Have you considered using machine vision... a camera I mean...

[rbtying]

Yeah, I wouldn't have needed help for the more conventional <= 1cm height, but the 1" is the absolute minimum height that I can lower the chassis to.  It can go higher, if needed, I believe.  I have considered machine vision, but would like to keep it as a last resort (many points of failure). 

Would you be able to recommend the LED/corresponding transistor?  I'm not too sure how to make it work reliably at longish ranges.

[billhowl]

http://www.seattlerobotics.org/encoder/200106/linerigel.html
This site will help you to build one that meet you range.