- Added pca9685 package 16-channel, 12-bit PWM controller with I2C

- Added servo package to control servos using pca9685 package

motion/servo/servo.go

@@ -0,0 +1,61 @@
+// Package servo allows control of servos using a PWM controller.
+package servo
+
+import (
+	"log"
+)
+
+// A PWM interface implements access to a pwm controller.
+type PWM interface {
+	SetPwm(n int, onTime int, offTime int) error
+}
+
+// A SERVO interface implements access to the servo.
+type Servo interface {
+	SetAngle(angle int) error
+
+	SetDebug(v bool)
+}
+
+type servo struct {
+	pwm  PWM
+	freq int
+	n    int
+
+	minms, maxms float64
+
+	debug bool
+}
+
+// New creates a new SERVO interface.
+// pwm: instance of a PWM controller.
+// freq: Frequency of pwm signal (typically 50Hz)
+// n: PWM channel of the pwm controller to be used
+// minms: Pulse width corresponding to servo position of 0deg
+// maxms: Pulse width corresponding to servo position of 180deg
+func New(pwm PWM, freq int, n int, minms, maxms float64) Servo {
+	return &servo{
+		pwm:   pwm,
+		freq:  freq,
+		n:     n,
+		minms: minms,
+		maxms: maxms,
+	}
+}
+
+// SetDebug is used to enable logging (debug mode).
+func (s *servo) SetDebug(v bool) {
+	s.debug = v
+}
+
+// SetAngle sets the servo angle.
+func (s *servo) SetAngle(angle int) error {
+	ms := s.minms + float64(angle)*(s.maxms-s.minms)/180
+	offTime := int(ms * float64(s.freq) * 4096 / 1000)
+
+	if s.debug {
+		log.Printf("servo: given angle %v calculated ms %2.2f offTime %v", angle, ms, offTime)
+	}
+
+	return s.pwm.SetPwm(s.n, 0, offTime)
+}