Split out hhio

hhio/ultrasonic.go

@@ -0,0 +1,88 @@
+package hhio
+
+import "context"
+import "errors"
+import "time"
+
+import "github.com/stianeikeland/go-rpio/v4"
+
+type Ultrasonic struct {
+	C chan float64
+
+	trig rpio.Pin
+	echo rpio.Pin
+}
+
+var timeout = errors.New("timed out waiting for device")
+
+func NewUltrasonic(ctx context.Context, trig, echo int) *Ultrasonic {
+	us := &Ultrasonic{
+		C:    make(chan float64),
+		trig: rpio.Pin(trig),
+		echo: rpio.Pin(echo),
+	}
+
+	us.trig.Output()
+	us.trig.Low()
+
+	us.echo.Input()
+
+	go us.loop(ctx)
+
+	return us
+}
+
+func (us *Ultrasonic) loop(ctx context.Context) {
+	for {
+		select {
+		case <-ctx.Done():
+			close(us.C)
+			return
+
+		default:
+			us.measure()
+		}
+	}
+}
+
+func (us *Ultrasonic) measure() {
+	deadline := time.NewTimer(200 * time.Millisecond)
+
+	us.trigger()
+
+	start := us.wait(rpio.High, deadline)
+	end := us.wait(rpio.Low, deadline)
+
+	if start.IsZero() || end.IsZero() {
+		return
+	}
+
+	duration := end.Sub(start)
+	cm := duration.Seconds() * 17150
+
+	if cm > 400 {
+		return
+	}
+
+	us.C <- cm
+}
+
+func (us *Ultrasonic) trigger() {
+	us.trig.High()
+	time.Sleep(10 * time.Microsecond)
+	us.trig.Low()
+}
+
+func (us *Ultrasonic) wait(goal rpio.State, deadline *time.Timer) time.Time {
+	for {
+		select {
+		case <-deadline.C:
+			return time.Time{}
+
+		default:
+			if us.echo.Read() == goal {
+				return time.Now()
+			}
+		}
+	}
+}