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embd/sensor/us020/us020.go

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// Package us020 allows interfacing with the US020 ultrasonic range finder.
package us020
import (
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"log"
"sync"
"time"
"github.com/stianeikeland/go-rpio"
)
const (
pulseDelay = 30000 * time.Nanosecond
defaultTemp = 25
)
type Thermometer interface {
Temperature() (float64, error)
}
type nullThermometer struct {
}
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func (*nullThermometer) Temperature() (float64, error) {
return defaultTemp, nil
}
var NullThermometer = &nullThermometer{}
// US020 represents a US020 ultrasonic range finder.
type US020 struct {
EchoPinNumber, TriggerPinNumber int
Thermometer Thermometer
echoPin rpio.Pin
triggerPin rpio.Pin
speedSound float64
initialized bool
mu sync.RWMutex
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Debug bool
}
// New creates a new US020 interface. The bus variable controls
// the I2C bus used to communicate with the device.
func New(e, t int, thermometer Thermometer) *US020 {
return &US020{EchoPinNumber: e, TriggerPinNumber: t, Thermometer: thermometer}
}
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
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d.echoPin.Input()
d.triggerPin.Output()
if d.Thermometer == nil {
d.Thermometer = NullThermometer
}
if temp, err := d.Thermometer.Temperature(); err == nil {
d.speedSound = 331.3 + 0.606*temp
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if d.Debug {
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log.Printf("read a temperature of %v, so speed of sound = %v", temp, d.speedSound)
}
} else {
d.speedSound = 340
}
d.initialized = true
return
}
// 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
}
if d.Debug {
log.Print("us020: trigerring pulse")
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}
// Generate a TRIGGER pulse
d.triggerPin.High()
time.Sleep(pulseDelay)
d.triggerPin.Low()
if d.Debug {
log.Print("us020: waiting for echo to go high")
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}
// Wait until ECHO goes high
for d.echoPin.Read() == rpio.Low {
}
startTime := time.Now() // Record time when ECHO goes high
if d.Debug {
log.Print("us020: waiting for echo to go low")
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}
// 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
}
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// Close.
func (d *US020) Close() {
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d.echoPin.Output()
rpio.Close()
}