added support for us020 ultra sonic range finder

AUTHORS

@@ -1,3 +1,4 @@
 Karan Misra <kidoman@gmail.com>
 Kunal Powar <kunalpowar1203@gmail.com>
 Nikesh Vora <nikesh.voratp@gmail.com>
+Akhil Sahdev <akhilsahdev@thoughtworks.com>

README.md

@@ -25,3 +25,9 @@ Use various sensors on the RaspberryPi with Golang (like a ninja!)
   Accelerometer and magnetometer
 
   [Documentation](http://godoc.org/github.com/kid0m4n/go-rpi/sensor/lsm303) [Datasheet](https://www.sparkfun.com/datasheets/Sensors/Magneto/LSM303%20Datasheet.pdf)
+
+### US020
+
+  Ultrasonic proximity sensor
+
+  [Documentation](http://godoc.org/github.com/kid0m4n/go-rpi/sensor/us020) [Product Page](http://www.digibay.in/sensor/object-detection-and-proximity?product_id=239)

samples/us020.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"log"
+	"time"
+
+	"github.com/kid0m4n/go-rpi/sensor/us020"
+)
+
+func main() {
+	rangeFinder := us020.New(10, 9)
+
+	for {
+		distance, err := rangeFinder.Distance()
+		if err != nil {
+			log.Panic(err)
+		}
+		log.Printf("Distance is %v", distance)
+
+		time.Sleep(500 * time.Millisecond)
+	}
+}

sensor/us020/us020.go

@@ -0,0 +1,97 @@
+// Package us020 allows interfacing with the US020 ultrasonic range finder.
+package us020
+
+import (
+	"sync"
+	"time"
+
+	"github.com/kid0m4n/go-rpi/sensor/bmp085"
+	"github.com/stianeikeland/go-rpio"
+)
+
+const (
+	pulseDelay = 30000 * time.Nanosecond
+)
+
+// A US020 implements access to a US020 ultrasonic range finder.
+type US020 interface {
+	// Distance computes the distance of the bot from the closest obstruction.
+	Distance() (float64, error)
+}
+
+type us020 struct {
+	echoPinNumber, triggerPinNumber int
+
+	echoPin    rpio.Pin
+	triggerPin rpio.Pin
+
+	speedSound float64
+
+	initialized bool
+	mu          *sync.RWMutex
+}
+
+// New creates a new US020 interface. The bus variable controls
+// the I2C bus used to communicate with the device.
+func New(e, t int) US020 {
+	return &us020{echoPinNumber: e, triggerPinNumber: t, mu: new(sync.RWMutex)}
+}
+
+func (d *us020) setup() (err error) {
+	d.mu.RLock()
+	if d.initialized {
+		d.mu.RUnlock()
+		return
+	}
+	d.mu.RUnlock()
+
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	if err = rpio.Open(); err != nil {
+		return
+	}
+
+	d.echoPin = rpio.Pin(d.echoPinNumber)       // ECHO port on the US020
+	d.triggerPin = rpio.Pin(d.triggerPinNumber) // TRIGGER port on the US020
+
+	temp, err := bmp085.Temperature()
+	if err != nil {
+		d.speedSound = 340
+	} else {
+		d.speedSound = 331.4 + 0.606*temp
+	}
+
+	d.initialized = true
+
+	return nil
+}
+
+// Distance computes the distance of the bot from the closest obstruction.
+func (d *us020) Distance() (distance float64, err error) {
+	if err = d.setup(); err != nil {
+		return
+	}
+
+	// Generate a TRIGGER pulse
+	d.triggerPin.High()
+	time.Sleep(pulseDelay)
+	d.triggerPin.Low()
+
+	// Wait until ECHO goes high
+	for d.echoPin.Read() == rpio.Low {
+	}
+
+	startTime := time.Now() // Record time when ECHO goes high
+
+	// Wait until ECHO goes low
+	for d.echoPin.Read() == rpio.High {
+	}
+
+	duration := time.Since(startTime) // Calculate time lapsed for ECHO to transition from high to low
+
+	// Calculate the distance based on the time computed
+	distance = float64(duration.Nanoseconds()) / 10000000 * (d.speedSound / 2)
+
+	return
+}