Hello everyone.

It's a wonderful sunny day here where I live today, so I decided to disassemble a small rubber ball that changed color when it was turned on (there is a simple on-off switch).

Of course, inside I found the 2 pins LED:


When I connect 3.3V on the center pin of the picture and GND on the left pin, the LED lights up constantly and every 2 seconds changes color (red to green to blue to purple).

I have several doubts that I would like to clarify with you:

1) The little black dot you see on the tip of the LED is the chip that regulates/varies the current? (which causes the color of the LED to vary)

2) The color of the LED is determined by the wavelength of the photons coming out of the depletion region, which, in turn, are determined by the bandgap of the material. So the type of semiconductor I choose based on the color I want to achieve. What I don't understand is "how" does the chip of the point 1 (or "what") control the different colors ... in theory it should control the composition of the semiconductor (but is that possible?)

3) The other possibility is that the LED in question is composed of three separate LEDs (not visible to the naked eye) ... each of which emits one of the primary colors: red, green, and blue. By controlling the intensity of each color, the LED can produce different shades and hues


I kindly ask you to solve these three doubts and/or explain to me how it works

 

Multicolor 2-pin LEDs can be created by having two different colored LEDs wired in opposite polarity.



You can test your LED with an ohmmeter. Connect the ohmmeter in both ways and see if you get a different color.

 

1) The little black dot you see on the tip of the LED is the chip that regulates/varies the current? (which causes the color of the LED to vary)

I can't see the dot very well because the encapsulation seems to be diffused and focus isn't good enough, but I suspect it's an integrated circuit.

2) The color of the LED is determined by the wavelength of the photons coming out of the depletion region, which, in turn, are determined by the bandgap of the material. So the type of semiconductor I choose based on the color I want to achieve. What I don't understand is "how" does the chip of the point 1 (or "what") control the different colors ... in theory it should control the composition of the semiconductor (but is that possible?)

I have some LEDs of that time and they consist of multiple LED die. Likely at least 3 (red, green, and blue) to be able to make all colors.

3) The other possibility is that the LED in question is composed of three separate LEDs (not visible to the naked eye) ... each of which emits one of the primary colors: red, green, and blue. By controlling the intensity of each color, the LED can produce different shades and hues

The IC controls the colors and intensity. You can't alter the colors, pattern, or intensity.

 

Multicolor 2-pin LEDs can be created by having two different colored LEDs wired in opposite polarity.

View attachment 318211

You can test your LED with an ohmmeter. Connect the ohmmeter in both ways and see if you get a different color.

So just because of those two LEDs I can see all the colors listed in the main post, right?
The fact that it is two LEDs I understand because there are 2 pins? (and not 3)
Because online I have often seen RGB LEDs

 

Multicolor 2-pin LEDs can be created by having two different colored LEDs wired in opposite polarity.

View attachment 318211

You can test your LED with an ohmmeter. Connect the ohmmeter in both ways and see if you get a different color.

In what sense?

If the 2 terminals of the LED in question are in the configuration in your picture .. regardless of which way I connect the ohmmeter I should see the same thing(?). What I mean is that if it was a single LED, I could figure out which of the two pins is the anode depending on the impedance measured .. but in this case it is not clear to me how to do it since the anode of the former is connected to the chatode of the latter.

 

The multicolor display LED, as described, includes three individual colored LED chips and a fair amount of digitaal logic inside the "small black blob. The different colors are the result of mixing the light colors , not changing the colors of each element. These LEDs are certainly great examples of what can be produced.

 

This is an example of such a device. It may not be identical to yours but the constructon will be the same.

As others have said, there are three LED chips (red, green, and blue) and an IC in the housing (your “black dot”). The IC varies the current to the 3 LEDs in a cycle, producing the various colors by mixing the R, G, and B light. You can make the same thing using a small μC and an RGB LED with four leads, or an addressable LED (e.g.: WS2812 or APA106), or with three discrete LEDs in red, green, and blue.

 

On much closer examination, what we see is a surface mounted LED assembly on a plastic support with an on/off switch above it in the photo. So really it is an assembly with an IC not shown. At least three IC devices and a fair amount of logic, well hidden.