raspi: add PWM example for Raspberry Pi

Signed-off-by: deadprogram <ron@hybridgroup.com>

examples/raspi_led_brightness.go

@@ -0,0 +1,39 @@
+// +build example
+//
+// Do not build by default.
+
+package main
+
+import (
+	"time"
+
+	"gobot.io/x/gobot"
+	"gobot.io/x/gobot/drivers/gpio"
+	"gobot.io/x/gobot/platforms/raspi"
+)
+
+func main() {
+	r := raspi.NewAdaptor()
+	led := gpio.NewLedDriver(r, "11")
+
+	work := func() {
+		brightness := uint8(0)
+		fadeAmount := uint8(15)
+
+		gobot.Every(100*time.Millisecond, func() {
+			led.Brightness(brightness)
+			brightness = brightness + fadeAmount
+			if brightness == 0 || brightness == 255 {
+				fadeAmount = -fadeAmount
+			}
+		})
+	}
+
+	robot := gobot.NewRobot("pwmBot",
+		[]gobot.Connection{r},
+		[]gobot.Device{led},
+		work,
+	)
+
+	robot.Start()
+}