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Sending MQTT Messages to AWS
Sterling-EWB Tutorials
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Sterling-EWB

Sending MQTT Messages to AWS using AT Command Firmware

This tutorial will show you how to connect the Sterling EWB to an Access Point and then send MQTT messages to AWS.

Required Tools

Prerequisites

  • You have flashed the AT Command Firmware into the Sterling EWB dev kit. To flash the firmware, simply download it from our website, connect to J24 of the dev kit, and then run the flash_AT.bat file included with the firmware.

  • You have an AWS account with IoT Core Service.

  • You have a Windows PC with Python 3.x.x installed. This demo was done with v3.9.1

  • You have downloaded the ATCommands_SampleApps from our website.

  • You have a WiFi access point to connect to the cloud.

Setup

Supply power to the development board via J24. Connect the TTL-232R-3V3 cable to J7 as shown below and then connect the other end of the cable to the your Windows PC. Then use Windows Device Manager determine the COM port for the TTL-232R-3V3. For this tutorial, we will use COM30.

Steps

  1. Login to your AWS IoT Service account and create a policy.

    • Navigate to Secure->Policies and then click Create a policy.

      CreatPolicy1-edit

    • Create the policy as shown below. For Action enter iot: Connect, iot:Publish. For Resource ARN enter *****. For Effect select Allow. This policy will allow devices (e.g. Sterling EWB) to connect and publish MQTT messages.

      CreatPolicy2-edit

    • If the policy was created successfully, you should see the screen below.

      CreatPolicy3-edit

  2. Create a Thing (i.e. Sterling EWB Sensor that will send MQTT messages).

    • Navigate to Manage->Things and then click Create things.

    • Select Create single thing and then click Next.

    • Name the Thing as MySensor and then click Next.

      CreatThing3-edit

    • Select Auto-generate a certificate and then click Next.

    • Attach the policy that we created to MySensor by selecting MyPolicy and then click Create thing.

      CreatThing5-edit

    • Download the MySensor certificate, public and private keys, and the Amazon Root CA certificates into the examples folder of the Python Samples Apps. Note, for this tutorial, we really just need the MySensor certificate and private keys, but you may download all the certificates and keys in case you need them in the future.

      Rename the downloaded MySensor certificate as MySensor.pem.crt. Rename the public key as MySensor.public.pem.key. Rename the private key as MySensor.private.pem.key.

    • MySensor is now created as shown below. Next click MySensor.

  3. Copy and save hostname/endpoint into a textfile.

    • Select the Interact tab and then click View Settings.

      CopyHost1-edit

    • Copy the endpoint url and save into a textfile. We will need this later when we run our Python sample scripts. It will be used as the hostname.

      CopyHost3-edit

  4. Setup the AWS MQTT Test Client.

    Navigate to Test->MQTT test client. Enter # on the Topic filter. Expand Additional configuration and select Display payload as strings. Then click Subscribe. # should be added to Subscriptions.

    TestMQTT

  5. Send MQTT messages from the EWB.

    • Open a cmd prompt on the ATCommands_SampleApps examples folder.

    • Connect to an access point using the join.py script.

      join.py -u COM30 -s NameOfYourAP -p YourPassphrase

    • Load the MySensor certifcate and private key into the EWB with the client_cert.py script.

      client_cert.py -u COM30 --cert MySensor.pem.crt --key MySensor.private.pem.key

    • Send a message with the mqtt.py script.

      mqtt.py -u COM30 -p 8883 --host TheEndPointURLYouCopiedFromStep3 --ssl NoVerifyHost --topic test/topic --body Hello

      CmdPrompt-Edit

    • The hello message is received on the AWS MQTT Test Client.

References