Lab 1 - AWS IoT Button

A couple years ago, AWS announced the AWS IoT Button you could order from Amazon.com. Why not create our own?

For this lab, our M5StickC will act as an AWS IoT Button, allowing you to trigger downstream AWS Services.

Configuration

In order to configure the code and your M5StickC for Lab1, you must change the following lines of code:

In file: ~/environment/workshop/include/lab_config.h

Replace:
#define LABCONFIG_LAB0_DO_NOTHING

With:
#define LABCONFIG_LAB1_AWS_IOT_BUTTON

Rebuild Code

cd ~/environment/workshop
cmake --build build

Flash Code

Please follow the same procedure from Flash the firmware files.

Result

What is going on, it’s not working? Could we have forgotten something? :)

The serial console returns the following error message:

...
E (15866) lab_connection: Failed to initialize the MQTT Connection: 1
E (15896) lab_connection: Exiting
...

Could our IoT Policy be incomplete?

If you recall when we set up our IoT Policy for our Thing we created it quite open, true, but we forgot an important Allow. Our IoT Policy Allowed Publishing, Subscribing and Receiving, but it did not allow Connecting! Go edit your policy, and add the following so that the document looks like:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "iot:Connect",
        "iot:Publish",
        "iot:Subscribe",
        "iot:Receive"
      ],
      "Resource": [
        "*"
      ]
    }
  ]
}

Reset the device, the device should connect without any problems.

Note: if you are using the M5StickC, there is a side button, pressing this side button will reboot the device.

Log into your AWS IoT Management console, use the web MQTT client and subscribe to the following topic:

mydevice/+

Click your M5StickC button: You should see the following JSON document flow on the broker

{
	"serialNumber": "[YOUR DEVICE SERIAL NUMBER]",
	"clickType": "SINGLE"
}

Hold your M5StickC button: You should see the following JSON document flow on the broker

{
	"serialNumber": "[YOUR DEVICE SERIAL NUMBER]",
	"clickType": "HOLD"
}

Done

You are done with Lab 1.

Knowledge check

• Q1: mydevice/+, what does the ”+” do?

The ”+” in the topic name, acts as a wildcard for that given section of the topic. There are 2 topic wildcards that can be used:

Wildcard	Description
#	Must be the last character in the topic to which you are subscribing. Works as a wildcard by matching the current tree and all subtrees. For example, a subscription to Sensor/# receives messages published to Sensor/, Sensor/temp, Sensor/temp/room1, but not the messages published to Sensor.
+	Matches exactly one item in the topic hierarchy. For example, a subscription to Sensor/+/room1 receives messages published to Sensor/temp/room1, Sensor/moisture/room1, and so on.

• Q2: What can you replace ”+” with?

In our IoT Button use-case, we saw that the button publishes to a topic that has m5stickc/[YOUR DEVICE SERIAL NUMBER]. In the MQTT client, if you subscribe to that specific topic (ie. mydevice/[YOUR DEVICE SERIAL NUMBER]), you will see the data coming only from your device.

Challenge

• Can you create an AWS IoT Rule that gets triggered on a button press and sends your cell phone an SMS?

This is achieved by first creating an AWS SNS Topic, creating a subscription to an SMS phone number. Here your phone number. Then, create an AWS IoT Rule with the following SQL statement:

SELECT * FROM 'mydevice/#'

Then select the AWS SNS topic you created as the action for the rule.

• Can you make that rule ONLY send you an SMS if you HOLD the button?

This is achieved by modifying your rule’s SQL query to have a where clause. Notice how when you click, the JSON object you receive has “clickType”: “SINGLE” and when you hold the button, you receive “clickType”: “HOLD”. Simply modify your SQL statement with:

SELECT * FROM 'mydevice/#' WHERE clickType = 'HOLD'

• Can you modify the AWS IoT Policy you created in prior steps to limit communications to only the required topics?

This is achieved by being more prescriptive on the topics that your device is allowed to publish to. For example, currently our device publishes on a topic like: mydevice/d8a01d551b1c. In that case, lets add that topic to the policy like so:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "iot:Connect",
        "iot:Subscribe",
        "iot:Receive"
      ],
      "Resource": [
        "*"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Publish",
      ],
      "Resource": [
        "arn:aws:iot:[REGION]:[AWS ACCOUNT ID]:topic/mydevice/d8a01d551b1c"
      ]
    }
  ]
}

Note: Make sure to replace REGION and AWS ACCOUNT ID with your specific region and account id.