Infrared color sensitivity

Thread Starter

rjwheaton

Joined Jan 26, 2014
5
I'm currently using a Lite-on phototransistor (LTR-4206E) and a Lite-on LED (LTE-4206) as part of a object recognition scheme. These are infrared devices. The idea is to detect the reflected infrared emissions from the object as they pass by. I cannot use a method where the infrared LED and phototransistor are facing each other, so I have to use reflected emissions.

My problem is that the system is much more sensitive to white objects as opposed to black or gray objects.

Is there a reasonable simple (and cheap) way to resolve this? I cannot put reflective tags or anything else on the objects.

Thanks in advance for your help.
 

ericgibbs

Joined Jan 29, 2010
18,766
hi rj,
Can you post a circuit diagram showing the Emitter and Detector circuits for this project.?
Also some indication of the highest and lowest reflected signal strengths.
E
 

crutschow

Joined Mar 14, 2008
34,285
Can't you just set the sensitivity to detect the least reflective object? Would the larger signal from a white object then be a problem, somehow?
 

Thread Starter

rjwheaton

Joined Jan 26, 2014
5
The problem is that there are other object behind the moving objects. And they are very often of a light color. So if I increase the sensitivity, I end up detecting the objects that are further away, and not of interest.
 

crutschow

Joined Mar 14, 2008
34,285
Are the objects behind stationary? If so they you can just detect changes in the signal from the moving objects and ignore the DC levels.

Otherwise can you put a black screen between the moving objects and the other objects?
 

THE_RB

Joined Feb 11, 2008
5,438
The Sharp brand GP2xxx sensors give an analogue voltage output that is related to the distance to the object.

Their internal electronics eliminates colour issues, and they give a reading that can indicate distance, no matter what colour the object is.

David Cook's excellent RobotRoom web site has a little tutorial on these sansors;
http://www.robotroom.com/DistanceSensor.html
 
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