云中树莓派（3）：通过 AWS IoT 控制树莓派上的 Led

云中树莓派（1）：环境准备

云中树莓派（2）：将传感器数据上传到AWS IoT 并利用Kibana进行展示

云中树莓派（3）：通过 AWS IoT 控制树莓派上的Led

云中树莓派（4）：利用声音传感器控制Led灯

 

1. Led 连接与测试

在某宝上买了几样配件，包括T型GPIO扩展板、40P排线、亚克力外壳、400孔面包板、若干杜邦线。现在我的树莓派长得这个样子了：

不由得感谢神奇的某宝，这些东西每一样都不超过三四块钱。

1.1 接线

以下几个简单步骤就完成了接线：

• 将排线一头插在树莓派的40个pin脚上，将另一头插在扩展板上。要注意方向，多试几次。还要注意在树莓派关机时候再插入。
• 把扩展板插在面包板上。
• 把Led 的长脚（正极）插在面包板第6行的任何一个孔内（对应GPIO18），将其短脚（负极或接地）插在第7行的任何一个孔内（对应GND）。

简单说下面包板。刚拿到手时还有点不知所措，稍微研究一下后就简单了。面包板为长方形，长边的两边是为了接电源的，每个长边都是联通的；中间区域内，每行内是联通的。

1.2 简单测试

下面的 python 能让led 灯每两秒钟亮一次：

import RPi.GPIO as GPIO
import time

PIN_NO=18
GPIO.setmode(GPIO.BCM)
GPIO.setup(PIN_NO, GPIO.OUT)
loopCount = 0
for x in xrange(500):
    print("Loop " + str(loopCount))
    GPIO.output(PIN_NO, GPIO.HIGH)
    time.sleep(2)
    GPIO.output(PIN_NO, GPIO.LOW)
    time.sleep(2)
    loopCount += 1

GPIO.cleanup()

也就是通过控制GPIO18的电压为高还是低来控制Led 灯是亮还是灭。

2. AWS IoT Device Shadow

AWS IoT 中一个功能叫做 Device Shadow，翻译为『设备影子』。它本质上为用于存储和检索设备的当前状态信息的 JSON 文档。Device Shadow 服务可以为您连接到 AWS IoT 的每台设备保留一个影子。您可以使用该影子通过 MQTT 或 HTTP 获取和设置设备的状态，无论该设备是否连接到 Internet。每台设备的影子都由相应事物的名称唯一标识。Device Shadow 服务充当中介，支持设备和应用程序检索和更新设备的影子。

 

AWS IoT 针对设备的影子提供了三项操作：

• UPDATE：如果设备的影子不存在，则创建一个该影子；如果存在，则使用请求中提供的数据更新设备的影子的内容。存储数据时使用时间戳信息，以指明最新更新时间。向所有订阅者发送消息，告知 desired 状态与 reported 状态之间的差异 (增量)。接收到消息的事物或应用程序可以根据 desired 状态和 reported 状态之间的差异执行操作。例如，设备可将其状态更新为预期状态，或者应用程序可以更新其 UI，以反映设备状态的更改。
• GET：检索设备的影子中存储的最新状态 (例如，在设备启动期间，检索配置和最新操作状态)。此操作将返回整个 JSON 文档，其中包括元数据。
• DELETE：删除设备的影子，包括其所有内容。这将从数据存储中删除 JSON 文档。您无法还原已删除的设备的影子，但可以创建具有相同名称的新影子。

也就是说，要通过 AWS IoT 来操作设备，需要通过设备影子进行。下图是控制Led 灯泡的示意图。外部应用和设备之间的交互通过设备影子进行。

Device Shadow 使用系统预留的 MQTT 主题来做应用程序和设备之间的通信：

MQTT 主题	用途
$aws/things/myLightBulb/shadow/update/accepted	当设备的影子更新成功时，Device Shadow 服务将向此主题发送消息
$aws/things/myLightBulb/shadow/update/rejected	当设备的影子更新遭拒时，Device Shadow 服务将向此主题发送消息
$aws/things/myLightBulb/shadow/update/delta	当检测到设备的影子的“reported”部分与“desired”部分之间存在差异时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/get/accepted	当获取设备的影子的请求获批时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/get/rejected	当获取设备的影子的请求遭拒时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/delete/accepted	当设备的影子被删除时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/delete/rejected	当删除设备的影子的请求遭拒时，Device Shadow 服务将向此主题发送消息。
$aws/things/myLightBulb/shadow/update/documents	每次设备的影子更新成功执行时，Device Shadow 服务都会向此主题发布状态文档。

下图显示了控制流程：

1. 连接着的 Led 灯发送封装在MQTT消息中的 reported 状态 『off』 到 AWS IoT
2. AWS IoT 通过 led 灯使用的证书来确定它所属的虚拟事物
3. AWS IoT 将 reported 状态保存在设备影子 JSON 文件中
4. 一条 AWS IoT rule 正监控着 led 的 off 状态，它发送一个消息到某个 SNS topic
5. 某 application 收到 SNS 消息。用户将 led 期望状态（desired state）设置为 on
6. AWS IoT 收到该消息，它更新设备影子中的 desired state，同时发送包含期望状态的 message 到某些topic。此时，reported 和 desired 状态是 『Out of Sync』的
7. led 收到 delta 消息，开始根据其中的 desired status 来设置其实际状态
8. led 将其状态设置为 on，向 MQTT topic 发送新的 reported 状态
9. AWS IoT 更新设备影子，现在该设备的 reported 和 desired 状态一致了 

3. Python 代码

代码一共就两个文件。文件 ledController.py 充当Led 灯的控制器，它定期向Led 发出『开』或『关』的指令，并定期获取其状态；文件 ledSwitch.py 充当 Led 等的操纵器，它通过调用树莓派的 GPIO 接口来设置和获取 led 灯的状态，以及将其状态上报给 IoT 服务。

AWS IoT  提供了 Device Shadow python SDK，因此不需要直接操作各种 MQTT 主题，而可以使用 get，update 和 delete 这种API。其地址在 https://github.com/aws/aws-iot-device-sdk-python/tree/master/AWSIoTPythonSDK/core/shadow。

3.1 ledController.py

from AWSIoTPythonSDK.MQTTLib import AWSIoTMQTTShadowClient
import logging
import time
import json
import threading

# Led shadow JSON Schema
#
# 
# Name: Led
# {
#     "state: {
#               "desired": {
#                          "light": 
#                }
#      }
#}

deviceShadowHandler = None

def getDeviceStatus():
    while True:
        print("Getting device status...\n")
        deviceShadowHandler.shadowGet(customShadowCallback_get, 50)
        time.sleep(60)    

def customShadowCallback_get(payload, responseStatus, token):
    if responseStatus == "timeout":
        print("Get request with token " + token + " time out!")
    if responseStatus == "accepted":
        print("========== Printing Device Current Status =========")
        print(payload)
        payloadDict = json.loads(payload)
        #{"state":{"desired":{"light":0},"reported":{"light":100}
        try:
            desired = payloadDict["state"]["desired"]["light"]
            desiredTime = payloadDict["metadata"]["desired"]["light"]["timestamp"]
        except Exception:
            print("Failed to get desired state and timestamp.")
        else:
            print("Desired status: " + str(desired) + " @ " + time.ctime(int(desiredTime)))

        try:
            reported = payloadDict["state"]["reported"]["light"]
            #"metadata":{"desired":{"light":{"timestamp":1533893848}},"reported":{"light":{"timestamp":1533893853}}}
            reportedTime = payloadDict["metadata"]["reported"]["light"]["timestamp"]
        except Exception:
            print("Failed to get reported time or timestamp")
        else:
            print("Reported status: " + str(reported) + " @ " + time.ctime(int(reportedTime)))
        
        print("=======================================\n\n")
    if responseStatus == "rejected":
        print("Get request with token " + token + " rejected!")

def customShadowCallback_upate(payload, responseStatus, token):
    # payload is a JSON string which will be parsed by jason lib
    if responseStatus == "timeout":
        print("Update request with " + token + " time out!")
    if responseStatus == "accepted":
        playloadDict = json.loads(payload)
        print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~")
        print("Update request with token: " + token + " accepted!")
        print("light: " + str(playloadDict["state"]["desired"]["light"]))
        print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n\n")
    if responseStatus == "rejected":
        print("Update request " + token + " rejected!")


def customShadowCallback_delete(payload, responseStatus, token):
    if responseStatus == "timeout":
        print("Delete request " + token + " time out!")
    if responseStatus == "accepted":
        print("Delete request with token " + token + " accepted!")
    if responseStatus == "rejected":
        print("Delete request with token " + token + " rejected!")

# Cofigure logging
logger = logging.getLogger("AWSIoTPythonSDK.core")
logger.setLevel(logging.ERROR)
streamHandler = logging.StreamHandler()
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
streamHandler.setFormatter(formatter)
logger.addHandler(streamHandler)

# AWS IoT Core endpoint. Need change some values to yours.
awsiotHost = "**********.iot.*********.amazonaws.com"
awsiotPort = 8883;
# AWS IoT Root Certificate. Needn't change.
rootCAPath = "/home/pi/awsiot/VeriSign-Class3-Public-Primary-Certification-Authority-G5.pem"
# Device private key. Need change to yours.
privateKeyPath = "/home/pi/awsiot/aec2731afd-private.pem.key"
# Device certificate. Need change to yours.
certificatePath = "/home/pi/awsiot/aec2731afd-certificate.pem.crt"
myAWSIoTMQTTShadowClient = None;
myAWSIoTMQTTShadowClient = AWSIoTMQTTShadowClient("RaspberryLedController")
myAWSIoTMQTTShadowClient.configureEndpoint(awsiotHost, awsiotPort)
myAWSIoTMQTTShadowClient.configureCredentials(rootCAPath, privateKeyPath, certificatePath)

myAWSIoTMQTTShadowClient.configureAutoReconnectBackoffTime(1, 32, 20)
myAWSIoTMQTTShadowClient.configureConnectDisconnectTimeout(60) # 10sec
myAWSIoTMQTTShadowClient.configureMQTTOperationTimeout(50) #5sec

#connect to AWS IoT
myAWSIoTMQTTShadowClient.connect()

#create a devcie Shadow with persistent subscription
thingName = "homepi"
deviceShadowHandler = myAWSIoTMQTTShadowClient.createShadowHandlerWithName(thingName, True)

#Delete shadow JSON doc
deviceShadowHandler.shadowDelete(customShadowCallback_delete, 50)

#start a thread to get device status every 5 seconds
statusLoopThread = threading.Thread(target=getDeviceStatus)
statusLoopThread.start()

#update shadow in a loop
loopCount = 0
while True:
    desiredState = "off"
    if (loopCount % 2 == 0):
        desiredState = "on"
    print("To change Led desired status to \"" + desiredState + "\" ...\n")
    jsonPayload = '{"state":{"desired":{"light":"' + desiredState + '"}}}'
    print("payload is: " + jsonPayload + "\n")
    deviceShadowHandler.shadowUpdate(jsonPayload, customShadowCallback_upate, 60)
    loopCount += 1
    time.sleep(60)

 

3.2 ledSwitch.py

import RPi.GPIO as GPIO
from AWSIoTPythonSDK.MQTTLib import AWSIoTMQTTShadowClient
import logging
import time
import json

# Led shadow JSON Schema
#
# 
# Name: Led
# {
#     "state: {
#               "desired": {
#                          "light": 
#                }
#      }
#}

LED_PIN_NUM = 18 # GPIO Number of Led long pin. Change to yours.
deviceShadowHandler = None
#initialize GOPI
GPIO.setmode(GPIO.BCM)
GPIO.setup(LED_PIN_NUM, GPIO.OUT)

def customShadowCallback_Delta(payload, responseStatus, token):
    # payload is a JSON string which will be parsed by jason lib
    print(responseStatus)
    print(payload)
    payloadDict = json.loads(payload)
    print("++++++++ Get DELTA data +++++++++++")
    desiredStatus = str(payloadDict["state"]["light"])
    print("desired status: " + desiredStatus)
    print("version: " + str(payloadDict["version"]))
    
    #get device current status
    currentStatus = getDeviceStatus()
    print("Device current status is " + currentStatus)
    #udpate device current status
    if (currentStatus != desiredStatus):
        # update device status as desired
        updateDeviceStatus(desiredStatus)
        # send current status to IoT service
        sendCurrentState2AWSIoT()
    print("+++++++++++++++++++++++++++\n")
    
def updateDeviceStatus(status):
    print("=============================")
    print("Set device status to " + status)
    if (status == "on"):
        turnLedOn(LED_PIN_NUM)
    else:
        turnLedOff(LED_PIN_NUM)
    print("=============================\n")

def getDeviceStatus():
    return getLedStatus(LED_PIN_NUM)

def turnLedOn(gpionum):
    GPIO.output(gpionum, GPIO.HIGH)

def turnLedOff(gpionum):
    GPIO.output(gpionum, GPIO.LOW)

def getLedStatus(gpionum):
    outputFlag = GPIO.input(gpionum)
    print("outputFlag is " + str(outputFlag))
    if outputFlag:
        return "on"
    else:
        return "off"    

def sendCurrentState2AWSIoT():
    #check current status of device
    currentStatus = getDeviceStatus()
    print("Device current status is " + currentStatus)
    print("Sending reported status to MQTT...")
    jsonPayload = '{"state":{"reported":{"light":"' + currentStatus + '"}}}'
    print("Payload is: " + jsonPayload + "\n")
    deviceShadowHandler.shadowUpdate(jsonPayload, customShadowCallback_upate, 50)
 
def customShadowCallback_upate(payload, responseStatus, token):
    # payload is a JSON string which will be parsed by jason lib
    if responseStatus == "timeout":
        print("Update request with " + token + " time out!")
    if responseStatus == "accepted":
        playloadDict = json.loads(payload)
        print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~")
        print(payload)
        print("Update request with token: " + token + " accepted!")
        print("light: " + str(playloadDict["state"]["reported"]["light"]))
        print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n\n")
    if responseStatus == "rejected":
        print("Update request " + token + " rejected!")

def customShadowCallback_Get(payload, responseStatus, token):
    print("responseStatus: " + responseStatus)
    print("payload: " + payload)
    payloadDict = json.loads(payload)
    # {"state":{"desired":{"light":37},"delta":{"light":37}},"metadata":{"desired":{"light":{"timestamp":1533888405}}},"version":54
    stateStr = "" 
    try:
        stateStr = stateStr + "Desired: " + str(payloadDict["state"]["desired"]["light"]) + ", "
    except Exception:
        print("No desired state")

    try:
        stateStr = stateStr + "Delta: " + str(payloadDict["state"]["delta"]["light"]) + ", "
    except Exception:
        print("No delta state")

    try:
        stateStr = stateStr + "Reported: " + str(payloadDict["state"]["reported"]["light"]) + ", "
    except Exception:
        print("No reported state") 
    
    print(stateStr + ", Version: " + str(payloadDict["version"]))

def printDeviceStatus():
    print("=========================")
    status = getDeviceStatus()
    print(" Current status: " + str(status))
    print("=========================\n\n")

# Cofigure logging
logger = logging.getLogger("AWSIoTPythonSDK.core")
logger.setLevel(logging.DEBUG)
streamHandler = logging.StreamHandler()
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
streamHandler.setFormatter(formatter)
logger.addHandler(streamHandler)

awsiotHost = "***********.iot.********.amazonaws.com"
awsiotPort = 8883;
rootCAPath = "/home/pi/awsiot/VeriSign-Class3-Public-Primary-Certification-Authority-G5.pem"
privateKeyPath = "/home/pi/awsiot/aec2731afd-private.pem.key"
certificatePath = "/home/pi/awsiot/aec2731afd-certificate.pem.crt"
myAWSIoTMQTTShadowClient = None;
myAWSIoTMQTTShadowClient = AWSIoTMQTTShadowClient("RaspberryLedSwitch")
myAWSIoTMQTTShadowClient.configureEndpoint(awsiotHost, awsiotPort)
myAWSIoTMQTTShadowClient.configureCredentials(rootCAPath, privateKeyPath, certificatePath)

myAWSIoTMQTTShadowClient.configureAutoReconnectBackoffTime(1, 32, 20)
myAWSIoTMQTTShadowClient.configureConnectDisconnectTimeout(60) # 10sec
myAWSIoTMQTTShadowClient.configureMQTTOperationTimeout(30) #5sec

#connect to AWS IoT
myAWSIoTMQTTShadowClient.connect()

#create a devcie Shadow with persistent subscription
thingName = "homepi"
deviceShadowHandler = myAWSIoTMQTTShadowClient.createShadowHandlerWithName(thingName, True)

#listen on deleta
deviceShadowHandler.shadowRegisterDeltaCallback(customShadowCallback_Delta)

#print the intital status
printDeviceStatus()

#send initial status to IoT service
sendCurrentState2AWSIoT()

#get the shadow after started
deviceShadowHandler.shadowGet(customShadowCallback_Get, 60)

#update shadow in a loop
loopCount = 0
while True:
    time.sleep(1)

3.3 主要过程

（1）ledSwitch.py 在运行后，获取led 的初始状态，并将其发给 AWS IoT 服务：

=========================
 outputFlag is 0
 Current status: off
=========================
outputFlag is 0
Device current status is off
Sending reported status to MQTT...
Payload is: {"state":{"reported":{"light":"off"}}}

（2）ledController.py 开始运行后，它首先获取led 的当前状态，为 『off』

（3）Controller 将其 desired 状态设置为 on

To change Led desired status to "on" ...
payload is: {"state":{"desired":{"light":"on"}}}

（4）Switch 收到 DELTA 消息，调用 GPIO 接口设置其状态，并向 IOT 服务报告其状态

{"version":513,"timestamp":1533983956,"state":{"light":"on"},"metadata":{"light":{"timestamp":1533983956}},"clientToken":"93dfc84c-c9f9-49fb-b844-d55203991208"}
++++++++ Get DELTA data +++++++++++
desired status: on
version: 513
outputFlag is 0
Device current status is off
=============================
Set device status to on
=============================
outputFlag is 1
Device current status is on
Sending reported status to MQTT...
Payload is: {"state":{"reported":{"light":"on"}}}

（5）Controller 获取最新状态

{"state":{"desired":{"light":"on"},"reported":{"light":"on"}},"metadata":{"desired":{"light":{"timestamp":1533983956}},"reported":{"light":{"timestamp":1533983957}}},"version":514,"timestamp":1533983959,"clientToken":"f24bcbbb-4b24-4354-b1df-349afdf23422"}
Desired status: on @ Sat Aug 11 18:39:16 2018
Reported status: on @ Sat Aug 11 18:39:17 2018

（6）循环往复

 

参考链接：

• https://www.linkedin.com/pulse/understanding-internet-things-aws-iot-kay-lerch/
• https://iotbytes.wordpress.com/device-shadows-part-1-basics/
• https://github.com/pradeesi/AWS-IoT-Shadows 
• https://github.com/aws/aws-iot-device-sdk-python/tree/master/samples/basicShadow
• https://raspi.tv/2013/rpi-gpio-basics-5-setting-up-and-using-outputs-with-rpi-gpio