IR Pairs don't detect dark objects well
jeffrey morris
Posts: 52
I found out that IR Pairs don't detect dark objects such as black pieces of furniture well. I built the BOE-BOT following Activity 4 on page 249. Which sensor detect objects of any colors? I tried to build the photoresistor circuit following Activity 1 on page 194 but the circuit didn't work at all even after following the trouble-shooting instructions on page 199.
Comments
Your finding is correct, but that isn't limited to just I/R, it's true of light in general, of which I/R is just part of the spectrum. Light WILL reflect off of white, light, or shiny surfaces better than it does off of dark, black or dull surfaces.
Just as a general matter, however, it is generally distance that is compromised, and not the complete object detection itself. In a case where the object absorbs ALL the light emitted (rare), then there would be no refelectivity at all, and thus no response would be seen.
If you have a video camera or digital camera with an LCD screen, you can view the actual emitted I/R light, to see if you're sending the beam where you expect it to be. If you see no light emitted, then there's obviously a bigger problem. I'd start there first before I went to other types of object detection.
To answer your question though, sonar (sound) is generally unaffected by the surface color of an object, but it is hampered by other things such as humidity, temperature, and to a small degree atmospheric pressure. The Parallax PING )) sensor is such a sonar object detection device.
Regards,
Bruce Bates
Post Edited (Bruce Bates) : 9/5/2005 2:18:56 PM GMT
A combination of IR, color sensor, and sonar would probably bring together the best robotic vision.
But, I haven't heard of anyone trying to do it [noparse][[/noparse]I don't have the color sensor].
Additionally, Optics can enhance the light sensors and data from focusing can actually be kept to calibrate to distance. The trick is to find a CCTV lens or a small pair of binoculars that you can integrate into your robot.
Nuts and Volts had a recent article on using the optical mouse chip as a primative camera. Actualy, this is quite a bit of data in a 16x16 matrix. Putting an adequate lens to it requires some manipulation, but can be done.
Still, even humans use their hands and feet as bumper when all else fails. So, it is a complex problem.
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