Tim’s Blog asks what would it take to build an addressable LED like the WS2812 (aka NeoPixel) using only discrete transistors? Time for a small “1960 style logic meets modern application” technology fusion project.

What exactly do we want to build? The diagram above shows how a system with our design would be set up. We have a microcontroller with a single data output line. Each “Pixel” module has a data input and a data output than can be used to connect many devices together by “daisy chaining”.

This is basically how the WS2812 works. To simplify things a bit, I had to make some concessions compared to the original WS2812:

• Each Pixel controls only a single LED that can be either turned on or off instead using pulse width modulation to allow greyscale (This can be implemented on the controller)
• Since only one bit of information is needed to turn the LED on or off, each LED will only accept a single bit of data.
• The LED will be immediately updated upon receipt of data, instead of latching only during “reset”.
• We don’t implement signal retiming of the data output. The data input will be buffered and directly forwarded to the output. This will lead to degradation of the signal timing after a while, but it is sufficient to control a few LEDs in cascade.

Read more on the blog post here

Learn more about NeoPixels on Adafruit here.