A proof of concept of a WS2811/WS2812/WS2812B client implementation for the RP2040, the microcontroller powering the new(ish) Raspberry Pi Pico. The WS2811 is a controller IC that understands the WS2811 protocol and drives an RGB led. WS2812/WS2812B are RGB leds with integrated WS2811 controllers.
The timing of the protocol is somewhat loosely defined. More information on the protocol can be found here.
This implementation uses the Programmable IO (PIO) interface in combination with DMA to run the implementation in parallel to the other microcontroller operations. It currently requires 31 PIO instructions and 2 DMA channels.
The code supports the emulation of 1 to 10 WS2811 chips.
Keep in mind that the RP2040 is a 3,3V microcontroller, whereas the WS2811 protocol uses at least 5V. This means that the data input and output lines cannot be directly connected to the RP2040.
In my testing, I used two resistors as a voltage divider to convert the input signal from 5V to 3,3V:
DATA_IN o---| 680 |---o---o RP2040
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#
# 1k
#
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GND
For the output signal, I used one channel of a 74HCT244 buffer IC to convert the 3,3V signal from the RP2040 back to the 5V signal required for the next WS2811.
- Using an of-the-shelf WS2811 controller and measuring its PWM outputs. This approach works somewhat, but is not straight forward to implement, since the WS2811 controllers do not generate a linear PWM waveform. There appears to not be any documentation on the exact PWM waveform, which makes the measurment a guessing game.
- Using AVR microcontrollers. AVR microcontrollers are too slow to measure and pass through the WS2811 signal.
- Using RP2040 bit-banging. If you do not want to use the PIO, you could also implement this using bit-banging. This would mean higher CPU overhead, but improve flexibility.
MIT