Making addressable LED like the WS2812 (aka NeoPixel) using only discrete transistors #NeoPixel
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.
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