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LED Testing
Mark Williams from United Kingdom  [2 posts]
3 years
Hi, I am looking to use Roborealm as part of a board production test that contains 42 LEDs spread across the PCB. Each LED can light red / green. The basic test is to light a position on the board either red/green and check the coordinates from Roborealm to ensure the LED lit the correct position and colour.

Under controlled tests I have been able to turn each LED on in turn and get an output from Robo realm into our test software. Robo realm provides the coordinates of the LED position.

I am having difficulty getting a reliable image to test from the webcam. It seems the nature of how the camera sees the LED is a bright white source that lights its surroundings the chosen colour (i.e. red/green). With any background light source reflecting on the board the colour distinction when the LED is turned on is even worse.

Has anyone had any experience producing a similar test to check LEDs? If so do you have any pointers as to how to achieve such a test.

I was considering using an external filter on the camera (red / green) in case the CCD sensor is being 'overloaded' by the point light source of the LED.

Thanks in advance, Mark
Steven Gentner from United States  [1371 posts] 3 years
Mark,

Common problem. Often seen when folks try to track laser lights too (the forum search should show a couple for further reading).

In a nutshell, switch off auto exposure in you webcam and really increase shutter speed which will really dim the image ... but the colors will be much stronger without the center white spot and will be detected much easier.

If your webcam doesn't allow you to turn off auto exposure, then buy another webcam. Anything around the $50 should have that feature and well worth the investment for a commercial app!

STeven.
Mark Williams from United Kingdom  [2 posts] 3 years
Thank you very much for your response.

I will try that today - I am using a Microsoft Lifecam HD which was a reasonably expensive camera so hopefully I can change the settings as you suggest.

Reflections on the PCB were another issue - I may be able to shroud the test fixture from factory lighting immediately above, but I will see how things are with your camera suggestions.

Thanks, Mark

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