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So this little board when connected to 5v and GND start blinking different colors in different orders and with different timing for colors to stay on! There is nothing on the board other than the LED and a resistor! How on earth does the LED know when to turn on/off? and how do the colors change? Please note, this is not an RGB LED. enter image description here

enter image description here

Please see the schematics here.

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  • \$\begingroup\$ While there are three connectors visible, two of them are GND. Why wouldn't this be an RGB LED? \$\endgroup\$
    – Mast
    Commented May 10, 2016 at 6:37
  • \$\begingroup\$ @Mast: nope, the LED itself only has two pins, the GNDs are tied together. But in a sense yes, since it has different colours, they are just not accessible from the outside. If you were to look at it with high magnification, then you would see individual LEDs as well as a little die which contains the necessary electronics for blinking and colour changing. \$\endgroup\$
    – PlasmaHH
    Commented May 10, 2016 at 8:33
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    \$\begingroup\$ This is an RGB led, but you cannot power the seperate LED's inside the package from the outside individually.. \$\endgroup\$
    – James T
    Commented May 10, 2016 at 8:51
  • \$\begingroup\$ There's a base cost for what you can actually package, which is about 400um x 400um. Anything smaller you cannot dice off the wafer. Your PN junctions do not take all of the space, and your pads have space under them, so you can throw some simple state machines in there. You make junction capacitors with reverse biased PNs and then have doping-based resistors. As you have a PN junction for the LED, you then name make a NPN that you can use as the drivers for the oscillating timer. You end up with an analog state machine. \$\endgroup\$
    – b degnan
    Commented May 10, 2016 at 10:51

2 Answers 2

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The led itself integrates an IC that takes care of everything. Here is a closeup of what these kind of LED look like:

Rainbow LED

You see that the LED actually integrates a very small circuit board, with the IC die placed on the bottom (you see the bonding wires), and three very small LED packages on the top (one for each color).

The IC integrates an oscillator, and drives each of the three LEDs with PWM to fade/blink the colors. Everything is inside the IC, it just needs to be powered. The circuit diagram would actually be very simple, each LED is simply connected to specific pads of the IC. Unfortunately, the documentation for such ICs are not available, because they are not usually sold separately. You have to buy the whole LED.

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This is an auto-flash LED with the flashing circuitry built into the LED package.

Similar to this product from Adafruit.

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    \$\begingroup\$ Any idea what the flashing circuitry looks like? Or would you be able to direct me to a link that goes into more detail? \$\endgroup\$
    – Arash
    Commented May 10, 2016 at 0:02
  • \$\begingroup\$ No idea! ------- \$\endgroup\$
    – Daniel
    Commented May 10, 2016 at 0:14
  • \$\begingroup\$ Try this sunfounder.com/wiki/… \$\endgroup\$ Commented May 10, 2016 at 1:08
  • \$\begingroup\$ @WhatRoughBeast That's just a schematic of the board. It doesn't include details on anything inside the LED. \$\endgroup\$
    – user39382
    Commented May 10, 2016 at 6:31

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