TLC5973 driver in Golang for Raspberry Pi

README.md

This is a simple example on how to interface with a TLC5973 IC to dim LEDs in Raspberry Pi.

It uses SPI to generate a pulse train with precise timing.

In Raspberry Pi, the SPI may have some inter-byte delay, which makes this useless. More here: https://www.raspberrypi.org/forums/viewtopic.php?t=211152

I'm using go-rpio to manage the SPI device.

The idea to use SPI came from this repo: https://github.com/mik4el/cc1350-swim-thermo/blob/b2fdb54a940e18911959a5e1778ca7fc06915a11/software/tlc5973_spimaster_CC1350_SWIMTHERMO_tirtos_ccs/spimaster.c

tlc5973.go

package core

import (
	"github.com/stianeikeland/go-rpio"
)

func setLed(intensity int) bool {
	if err := rpio.Open(); err != nil {
		fmt.Println("Could not open SPI device")
		return false
	}
	defer rpio.Close()

  // TLC5973 Board, using SPI comm

  spiDev := rpio.Spi0
  switch led.DevID {
  case 0:
    spiDev = rpio.Spi0
  case 1:
    spiDev = rpio.Spi1
  case 2:
    spiDev = rpio.Spi2
  default:
    fmt.Println("Using default SPI device")
    spiDev = rpio.Spi0
  }
  if err := rpio.SpiBegin(spiDev); err != nil {
    fmt.Println("Could not begin SPI device")
    return false
  }
  rpio.SpiSpeed(500000)
  rpio.SpiTransmit(generateTlcPayload(intensity)...)
  rpio.SpiEnd(rpio.Spi0)

  return true
}

func generateTlcPayload(intensity int) (out []byte) {
	const (
		ONE  byte = 0xA // 0b1010
		ZERO byte = 0x8 // 0b1000
		NONE byte = 0x0 // 0b0000
	)

	out = []byte{NONE, NONE, NONE, NONE}

	intensity = intensity & 0xFFF

	buf := []int16{0x3AA, intensity, intensity, intensity}

	for _, rawWord := range buf {
		for b := 0; b < 6; b++ {
			var word byte = ZERO
			if rawWord&0x800 > 0 {
				word = ONE
			}
			rawWord <<= 1
			word <<= 4
			word |= ZERO
			if rawWord&0x800 > 0 {
				word |= ONE
			}
			rawWord <<= 1
			out = append(out, word)
		}
	}
	out = append(out, NONE)
	out = append(out, NONE)
	out = append(out, NONE)
	out = append(out, NONE)
	return
}