0x3333 · July 24, 2020 11:46 · Jul 24, 2020
diff --git a/README.md b/README.md
@@ -0,0 +1,9 @@
+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
diff --git a/tlc5973.go b/tlc5973.go
@@ -0,0 +1,73 @@
+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
+}
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