https://github.com/tomarrell/rasp-ws2812b
Controlling WS2812b LED's using Rust on the Raspberry Pi
https://github.com/tomarrell/rasp-ws2812b
embedded leds mario pwm raspberry-pi rust spi
Last synced: about 1 year ago
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Controlling WS2812b LED's using Rust on the Raspberry Pi
- Host: GitHub
- URL: https://github.com/tomarrell/rasp-ws2812b
- Owner: tomarrell
- Created: 2018-08-02T14:30:01.000Z (almost 8 years ago)
- Default Branch: master
- Last Pushed: 2019-07-15T22:10:28.000Z (almost 7 years ago)
- Last Synced: 2025-03-31T03:01:42.926Z (about 1 year ago)
- Topics: embedded, leds, mario, pwm, raspberry-pi, rust, spi
- Language: Rust
- Homepage: https://blog.tomarrell.com/post/rust_and_leds
- Size: 310 KB
- Stars: 18
- Watchers: 2
- Forks: 5
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
**NB: This was an experiment, and should not actually be used as a method to communicate with the WS2812b**
# Rasp-WS2812b
Power WS2812b LEDs from your Raspberry Pi over SPI.
[Blogpost](https://blog.tomarrell.com/post/rust_and_leds)
## How it works?
The LEDs run with a scan frequency of no less than `400Hz`, with a data transfer rate of `800kbps`.
The traditional method of communication with the WS2812b is usually PWM. The duty cycle to send a single bit is:
| Bit | Time High | Time Low | Duty % |
|-----|-----------|----------|--------|
| 0 | 0.4us | 0.85us | 32% |
| 1 | 0.8us | 0.45us | 64% |
A visual of the protocol is below.
```
PWM LED (0): where
on time = 0.4us +/-150ns
off time = 0.85us +/-150ns
Volts
| START END
| v v
| ----------
| | |
| | |
| | |
| ---- -------------------
*-------------------------------- Time
PWM LED (1): where
on time = 0.8us +/-150ns
off time = 0.45us +/-150ns
Volts
| START END
| v v
| ------------------
| | |
| | |
| | |
| ---- -----------
*-------------------------------- Time
```
Looking at the above duty cycle lengths, we can approximate each time slice into another 3 periods, each **33%** of the original wavelength in order to have constant high/low runs for the given period. This will allow us to continue using SPI, using a clock speed of approximately `3Mhz`.
To interact over SPI, each traditional LED sequence (3 bytes, 8 bits per colour channel) needs to be converted to a 9 byte sequence (72 bits per colour channel) before being shifted over SPI. Each traditional PWM 'bit' gets turned into an equivalent 3 SPI bits, and the clock speed of the SPI interface set to achieve within the `+/-150ns` error margins.
With the traditional period broken into 3 time sections, each can be pulled high or low individually. We can therefore represent what would have been a PWM (1) with an SPI `110`. And on the contrary, represent a PWM (0) with an SPI `100`.
## Example
An example of a Raspberry Pi controlling a flexible panel of WS2812b's:
(Mario)
## License
Licensed under the GNU GPLv3.0