mcp9808: add experimental support for digital temperature sensor (#356)

* mcp9808: add support for digital temperature sensor

Add support for microchip i2c MCP9808 temperature sensor.

experimental/cmd/mcp9808/main.go

@@ -0,0 +1,74 @@
+// 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.
+
+// mcp9808 communicates with an mcp9808 sensor reading ambient temperature.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+
+	"periph.io/x/periph/conn/i2c/i2creg"
+	"periph.io/x/periph/experimental/devices/mcp9808"
+	"periph.io/x/periph/host"
+)
+
+func mainImpl() error {
+	if _, err := host.Init(); err != nil {
+		return err
+	}
+	address := flag.Int("address", 0x18, "I²C address")
+	i2cbus := flag.String("bus", "", "I²C bus (/dev/i2c-1)")
+
+	flag.Parse()
+
+	fmt.Println("Starting MCP9808 Temperature Sensor")
+	if _, err := host.Init(); err != nil {
+		return err
+	}
+
+	// Open default I²C bus.
+	bus, err := i2creg.Open(*i2cbus)
+	if err != nil {
+		return fmt.Errorf("failed to open I²C: %v", err)
+	}
+	defer bus.Close()
+
+	// Create a new temperature sensor a sense with default options.
+	sensor, err := mcp9808.New(bus, &mcp9808.Opts{Addr: *address})
+	if err != nil {
+		return fmt.Errorf("failed to open new sensor: %v", err)
+	}
+
+	// Read values from sensor every second.
+	everySecond := time.Tick(time.Second)
+	var halt = make(chan os.Signal)
+	signal.Notify(halt, syscall.SIGTERM)
+	signal.Notify(halt, syscall.SIGINT)
+
+	fmt.Println("ctrl+c to exit")
+	for {
+		select {
+		case <-everySecond:
+			t, err := sensor.SenseTemp()
+			if err != nil {
+				return fmt.Errorf("sensor reading error: %v", err)
+			}
+			fmt.Println(t)
+		case <-halt:
+			return nil
+		}
+	}
+}
+
+func main() {
+	if err := mainImpl(); err != nil {
+		fmt.Fprintf(os.Stderr, "mcp9808: %s.\n", err)
+		return
+	}
+}

experimental/devices/mcp9808/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 mcp9808 controls a Microchip MCP9808 digital I²C temperature sensor.
+//
+// Features
+//
+// -40°C and +125°C Operating Range.
+//
+// User-Selectable Measurement Resolution: +0.5°C, +0.25°C, +0.125°C, +0.0625°C.
+//
+// User-Programmable Temperature Alerts.
+//
+// Datasheet
+//
+// http://ww1.microchip.com/downloads/en/DeviceDoc/25095A.pdf
+package mcp9808

experimental/devices/mcp9808/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 mcp9808_test
+
+import (
+	"fmt"
+	"log"
+
+	"periph.io/x/periph/conn/i2c/i2creg"
+	"periph.io/x/periph/conn/physic"
+	"periph.io/x/periph/experimental/devices/mcp9808"
+	"periph.io/x/periph/host"
+)
+
+func ExampleDev_SenseTemp() {
+	// 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 temperature sensor.
+	sensor, err := mcp9808.New(bus, &mcp9808.DefaultOpts)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// Read values from sensor.
+	measurement, err := sensor.SenseTemp()
+
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	fmt.Println(measurement)
+}
+
+func ExampleDev_SenseWithAlerts() {
+	// 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 temperature sensor.
+	sensor, err := mcp9808.New(bus, &mcp9808.DefaultOpts)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	lower := physic.ZeroCelsius
+	upper := physic.ZeroCelsius + 25*physic.Celsius
+	critical := physic.ZeroCelsius + 32*physic.Celsius
+
+	// Read values from sensor.
+	temperature, alerts, err := sensor.SenseWithAlerts(lower, upper, critical)
+
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	for _, alert := range alerts {
+		fmt.Println(alert)
+	}
+
+	fmt.Println(temperature)
+}