bh1750: Add support for ambient light sensor (#302)

experimental/devices/bh1750/bh1750.go

@@ -0,0 +1,140 @@
+// Copyright 2018 The Periph Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package bh1750
+
+import (
+	"encoding/binary"
+	"time"
+
+	"periph.io/x/periph/conn/i2c"
+	"periph.io/x/periph/conn/physic"
+)
+
+// I2CAddr i2c default address.
+const I2CAddr uint16 = 0x23
+
+// AlternativeI2CAddr i2c alternative address.
+const AlternativeI2CAddr uint16 = 0x5c
+
+// Resolution represents the measurements modes.
+type Resolution uint8
+
+const (
+	// ContinuousHighResMode start measurement at 1lx resolution. Measurement time is approx 120ms.
+	ContinuousHighResMode Resolution = 0x10
+
+	// ContinuousHighResMode2 start measurement at 0.5lx resolution. Measurement time is approx 120ms.
+	ContinuousHighResMode2 Resolution = 0x11
+
+	// ContinuousLowResMode start measurement at 4lx resolution. Measurement time is approx 16ms.
+	ContinuousLowResMode Resolution = 0x13
+
+	// OneTimeHighResMode measurement at 1lx resolution and the device is automatically set to Power Down after measurement.
+	OneTimeHighResMode Resolution = 0x20
+
+	// OneTimeHighResMode2 measurement at 0.5lx resolution and the device is automatically set to Power Down after measurement.
+	OneTimeHighResMode2 Resolution = 0x21
+
+	// OneTimeLowResMode measurement at 4lx resolution and the device is automatically set to Power Down after measurement.
+	OneTimeLowResMode Resolution = 0x23
+
+	safetyTimeout = 20 * time.Millisecond
+)
+
+// Map of timeouts for measurement type.
+var timeout = map[Resolution]time.Duration{
+	ContinuousHighResMode:  120*time.Millisecond + safetyTimeout,
+	ContinuousHighResMode2: 120*time.Millisecond + safetyTimeout,
+	ContinuousLowResMode:   16*time.Millisecond + safetyTimeout,
+	OneTimeHighResMode:     120*time.Millisecond + safetyTimeout,
+	OneTimeHighResMode2:    120*time.Millisecond + safetyTimeout,
+	OneTimeLowResMode:      16*time.Millisecond + safetyTimeout,
+}
+
+// Mode - device mode.
+type Mode uint8
+
+const (
+	// PowerDown - no active state.
+	PowerDown Mode = 0x00
+
+	// PowerOn - waiting for measurement command.
+	PowerOn Mode = 0x01
+)
+
+const (
+	dataRegister            uint8 = 0x00
+	measurementTimeRegister uint8 = 0x45
+	reset                   uint8 = 0x07
+)
+
+// Dev is a handler to bh1750 controller
+type Dev struct {
+	dev  i2c.Dev
+	res  Resolution
+	mode Mode
+}
+
+// NewI2C opens a handle to an bh1750 sensor.
+//
+// To use on the default address, bh1750.I2CAddr must be passed as argument.
+func NewI2C(bus i2c.Bus, address uint16) (*Dev, error) {
+	dev := &Dev{dev: i2c.Dev{Bus: bus, Addr: address}}
+
+	if err := dev.init(); err != nil {
+		return nil, err
+	}
+	return dev, nil
+}
+
+func (d *Dev) init() error {
+	if err := d.SetMode(PowerOn); err != nil {
+		return err
+	}
+
+	if err := d.SetResolution(ContinuousHighResMode); err != nil {
+		return err
+	}
+
+	_, err := d.dev.Write([]byte{reset})
+	return err
+}
+
+// SetMode set the sleep mode of the sensor.
+func (d *Dev) SetMode(m Mode) error {
+	d.mode = m
+	_, err := d.dev.Write([]byte{reset})
+	return err
+}
+
+// SetResolution set the resolution mode of the sensor.
+func (d *Dev) SetResolution(r Resolution) error {
+	d.res = r
+	_, err := d.dev.Write([]byte{byte(r)})
+	return err
+}
+
+// Sense reads the light value from the bh1750 sensor.
+func (d *Dev) Sense() (physic.LuminousFlux, error) {
+	if err := d.SetResolution(d.res); err != nil {
+		return 0, err
+	}
+
+	time.Sleep(timeout[d.res])
+
+	buf := [2]byte{}
+	if err := d.dev.Tx([]byte{byte(d.res)}, buf[:]); err != nil {
+		return 0, err
+	}
+
+	rawValue := binary.BigEndian.Uint16(buf[:])
+	lux := physic.LuminousFlux(float64(rawValue) / 1.2)
+	return lux * physic.Lumen, nil
+}
+
+// Halt turn off device.
+func (d *Dev) Halt() error {
+	return d.SetMode(PowerDown)
+}

experimental/devices/bh1750/doc.go

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+// Copyright 2018 The Periph Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+// Package bh1750 controls a ROHM BH1750 ambient light sensor, over an i2c bus.
+//
+// Datasheet
+//
+// http://cpre.kmutnb.ac.th/esl/learning/bh1750-light-sensor/bh1750fvi-e_datasheet.pdf
+package bh1750

experimental/devices/bh1750/example_test.go

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+// Copyright 2018 The Periph Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package bh1750_test
+
+import (
+	"fmt"
+	"log"
+
+	"periph.io/x/periph/conn/i2c/i2creg"
+	"periph.io/x/periph/experimental/devices/bh1750"
+	"periph.io/x/periph/host"
+)
+
+func Example() {
+	// Make sure periph is initialized.
+	if _, err := host.Init(); err != nil {
+		log.Fatal(err)
+	}
+
+	// Open default I²C bus.
+	bus, err := i2creg.Open("")
+	if err != nil {
+		log.Fatalf("failed to open I²C: %v", err)
+	}
+	defer bus.Close()
+
+	// Create a new light sensor.
+	sensor, err := bh1750.NewI2C(bus, bh1750.I2CAddr)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// Read value from sensor.
+	measurement, err := sensor.Sense()
+
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	fmt.Println(measurement)
+}