Consideration of how to verify/proof large quantities of RGB LEDs for cube  - Page 1
Forum section: electronics / projects

author: t1d
author_rank: Super Contributor
timestamp: December 12, 2020, 04:20:33 pm
content: It seems to me that visually proofing large quantities of individual LEDs and, later, the resulting panels would be tedious and easily miss a fault. I have seen jigs that use a MCU to rotate through the different colors. But, I have not seen a method for automating the visual verification. So, I wanted to start a discussion in that regard.It would seem to be a straight forward matter of adding a light sensor to the test jig MCU and have that verify the LED's operations. The MCU would illuminate a color and test for a voltage returned by a phototransistor, or other means/sensor. If a fault is detected, the MCU would flash the last LED color that was good. The builder would know that the next LED color was the location of the fault. A cardboard box might be used to eliminate ambient light.These are just some of my quick thoughts. What other issues and methods do you foresee?

author: Someone
author_rank: Super Contributor
timestamp: December 12, 2020, 09:35:56 pm
content: Why re-invent a testing machine? Surely there are suppliers who sell (factory) tested parts?

author: CJay
author_rank: Super Contributor
timestamp: December 12, 2020, 09:46:06 pm
content: Pretty simple, photodiode, microcontroller, dark box.Light one LED, measure photodiode output, repeat until all LEDs and colours are done.Want to get fancy?Measure and record photodiode output and you can get a rough match of luminous output (might be difficult as incident angle changes in a panel)

author: Benta
author_rank: Super Contributor
timestamp: December 12, 2020, 10:10:51 pm
content: Quote from: Someone on December 12, 2020, 09:35:56 pm^ This.It's referred to as "binning" and reputable suppliers offer this. They will normally not sell a specific "bin", but guarantee that all parts in a batch belong to the same bin."Bin" means same brightness and same color wavelength, for white LEDs it's brightness and color temperature.Of course, if you've just bought a Chinese "grab bag" of LEDs, you're on your own.

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 12, 2020, 10:44:58 pm
content: Measure the supply current while lighting the LEDs one at a time. Take note if the current is either lower or higher than expected. LEDs very rarely fail in a way where they draw the usual operating current without emitting light - they normally fail open or shorted.

author: t1d
author_rank: Super Contributor
timestamp: December 13, 2020, 04:33:21 am
content: All great comments; thanks! Keep 'em coming.I like NiHaoMike's idea to read the LEDs current. No sensor needed.I know PICs can measure voltage. Add a current sense resistor and you can get there.

author: jonpaul
author_rank: Super Contributor
timestamp: December 13, 2020, 10:35:24 am
content: Cost to test will greatly exceed LED value.Buy from reputable supplier like CREE, you will pay more than the Chinese junk, but get a much better product and spec.Jon

author: CJay
author_rank: Super Contributor
timestamp: December 13, 2020, 01:45:36 pm
content: Quote from: t1d on December 13, 2020, 04:33:21 amYep, what NiHaoMike said, current drawn is a good way to do it, simple, fast and effective

author: poorchava
author_rank: Super Contributor
timestamp: December 13, 2020, 02:09:28 pm
content: Use a color sensor. Company by the name Taos make these. Not expensive at all. Absolute color may not be guaranteed, but if it is the same between several LEDs, the output from sensor is the same.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 13, 2020, 02:15:39 pm
content: My main question is why bother. If you are getting significant numbrs that are out of spec, you should be buying better LEDs.Anything that has a bin code on the reel will already have been tested by the manufacturer.If you work on the assumption that most will be OK, would it not be easier and quicker to just build it and replace any dodgy LEDs, than test all of them ?