Added HC-SR04 ultrasonic distance sensor. (#143)

* Added HC-SR04 ultrasonic distance sensor.

Makefile

@@ -49,6 +49,8 @@ smoke-test:
 	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=feather-m0 ./examples/gps/uart/main.go
 	@md5sum ./build/test.hex
+	tinygo build -size short -o ./build/test.hex -target=itsybitsy-m0 ./examples/hcsr04/main.go
+	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=microbit ./examples/hd44780/customchar/main.go
 	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=microbit ./examples/hd44780/text/main.go

README.md

@@ -73,6 +73,7 @@ The following 46 devices are supported.
 | [ESP8266/ESP32 AT Command set for WiFi/TCP/UDP](https://github.com/espressif/esp32-at) | UART |
 | [GPS module](https://www.u-blox.com/en/product/neo-6-series) | I2C/UART |
 | [HD44780 LCD controller](https://www.sparkfun.com/datasheets/LCD/HD44780.pdf) | GPIO |
+| [HC-SR04 Ultrasonic distance sensor](https://cdn.sparkfun.com/datasheets/Sensors/Proximity/HCSR04.pdf) | GPIO |
 | [HUB75 RGB led matrix](https://cdn-learn.adafruit.com/downloads/pdf/32x16-32x32-rgb-led-matrix.pdf) | SPI |
 | [ILI9341 TFT color display](https://cdn-shop.adafruit.com/datasheets/ILI9341.pdf) | SPI |
 | [L293x motor driver](https://www.ti.com/lit/ds/symlink/l293d.pdf) | GPIO/PWM |

easystepper/easystepper.go

@@ -18,8 +18,7 @@ type DualDevice struct {
 	devices [2]Device
 }
 
-// New returns a new easystepper driver given 4 pins numbers (not pin object),
-// number of steps and rpm
+// New returns a new easystepper driver given 4 pins, number of steps and rpm
 func New(pin1, pin2, pin3, pin4 machine.Pin, steps int32, rpm int32) Device {
 	return Device{
 		pins:      [4]machine.Pin{pin1, pin2, pin3, pin4},
@@ -34,8 +33,7 @@ func (d *Device) Configure() {
 	}
 }
 
-// NewDual returns a new dual easystepper driver given 8 pins numbers (not pin object),
-// number of steps and rpm
+// NewDual returns a new dual easystepper driver given 8 pins, number of steps and rpm
 func NewDual(pin1, pin2, pin3, pin4, pin5, pin6, pin7, pin8 machine.Pin, steps int32, rpm int32) DualDevice {
 	var dual DualDevice
 	dual.devices[0] = Device{

examples/hcsr04/main.go

@@ -0,0 +1,20 @@
+package hcsr04
+
+import (
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/hcsr04"
+)
+
+func main() {
+	sensor := hcsr04.New(machine.D10, machine.D9)
+	sensor.Configure()
+
+	println("Ultrasonic starts")
+	for {
+		println("Distance:", sensor.ReadDistance(), "mm")
+
+		time.Sleep(100 * time.Millisecond)
+	}
+}

hcsr04/hcsr04.go

@@ -0,0 +1,81 @@
+// Package hcsr04 provides a driver for the HC-SR04 ultrasonic distance sensor
+//
+// Datasheet:
+// https://cdn.sparkfun.com/datasheets/Sensors/Proximity/HCSR04.pdf
+package hcsr04
+
+import (
+	"machine"
+	"time"
+)
+
+const TIMEOUT = 23324 // max sensing distance (4m)
+
+// Device holds the pins
+type Device struct {
+	trigger machine.Pin
+	echo    machine.Pin
+}
+
+// New returns a new ultrasonic driver given 2 pins
+func New(trigger, echo machine.Pin) Device {
+	return Device{
+		trigger: trigger,
+		echo:    echo,
+	}
+}
+
+// Configure configures the pins of the Device
+func (d *Device) Configure() {
+	d.trigger.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	d.echo.Configure(machine.PinConfig{Mode: machine.PinInput})
+}
+
+// ReadDistance returns the distance of the object in mm
+func (d *Device) ReadDistance() int32 {
+	pulse := d.ReadPulse()
+
+	// sound speed is 343000 mm/s
+	// pulse is roundtrip measured in microseconds
+	// distance = velocity * time
+	// 2 * distance = 343000 * (pulse/1000000)
+	return (pulse * 1715) / 10000 //mm
+}
+
+// ReadPulse returns the time of the pulse (roundtrip) in microseconds
+func (d *Device) ReadPulse() int32 {
+	t := time.Now()
+	d.trigger.Low()
+	time.Sleep(2 * time.Microsecond)
+	d.trigger.High()
+	time.Sleep(10 * time.Microsecond)
+	d.trigger.Low()
+	i := uint8(0)
+	for {
+		if d.echo.Get() {
+			t = time.Now()
+			break
+		}
+		i++
+		if i > 10 {
+			if time.Since(t).Microseconds() > TIMEOUT {
+				return 0
+			}
+			i = 0
+		}
+	}
+	i = 0
+	for {
+		if !d.echo.Get() {
+			return int32(time.Since(t).Microseconds())
+		}
+		i++
+		if i > 10 {
+			if time.Since(t).Microseconds() > TIMEOUT {
+				return 0
+			}
+			i = 0
+		}
+	}
+	return 0
+}