Developer David Johnson-Davies has written a driver for WS2812 programmable LED strips, together with Adafruit’s NeoPixel boards, which runs totally on an eight-bit Microchip AVR microcontroller — making use of its SPI bus to get the efficiency as much as snuff.
“WS2812 shows, nicknamed NeoPixels by Adafruit, are a preferred chainable kind of RGB LED show now obtainable in all kinds of codecs,” Johnson-Davies explains by means of background. “They use a non-standard protocol consisting of a serial stream of pulses, with the width of every pulse figuring out whether or not it’s a ‘0’ or a ‘1’. Nevertheless the pulses are very quick: a zero is outlined as having a width of 350ns, which is simply 8.4 cycles on a 24MHz CPU. Most NeoPixel libraries subsequently use hand-crafted assembler routines tailor-made to every processor for the low-level pulse technology.”
In case you’re trying to run NeoPixel LEDs from a Microchip AVR, there’s now a sensible driver for that. (📷: David Johnson-Davies)
Johnson-Davies, although, selected another strategy. Impressed by current tasks to make use of the programmable enter/output (PIO) capabilities of the Raspberry Pi RP2040 and RP2350 microcontroller households to drive WS2812 LED strips, Johnson-Davies determined to see if it was potential to do one thing related on a Microchip AVR microcontroller — an eight-bit household that, within the AVR128DA28 picked for the venture, runs at simply 24MHz.
“This AVR NeoPixel driver makes use of the SPI peripheral to generate the serial stream of bits,” Johnson-Davies explains, “a Timer/Counter to generate waveforms with the suitable pulse widths for the ‘0’ and ‘1’ bits, and the Configurable Customized Logic (CCL) to mix these indicators right into a single stream of pulses encoding the colours. This software would most likely work utilizing most members of the AVR DA, DB, and DD households.”
The venture, which makes use of solely one of many ADV128DA28’s two SPI peripherals, is documented in full on Johnson-Davies’ web site, full with supply code below the Artistic Commons Attribution 4.0 Worldwide license. “We may go one stage additional, and use the AVR Occasions System to get rid of a lot of the interconnections between the pins on the […] circuit with out affecting its operation,” the developer notes. “I am going to describe how to do that in a subsequent article.”
