In this project, I demonstrate developing a custom Alexa skill to fly and control a DJI Tello drone.

This project explores the key IoT platform aspects like device registry, device shadows (aka device twins) provided by AWS IoT service to enable communication between Raspberry Pi Zero, DJI Tello drone and a custom Amazon Alexa skill giving the ability to control the drone via voice commands.

In case you missed my first project on controlling DJI Tello drone with Xbox Controller, here is the link to it.

Here is a short video where I am flying the drone using Alexa voice commands:

This project will also enable you to implement other ideas on similar lines or different since the blocks/services/concepts used here are very much needed for developing any IoT application.

Following is the tech stack used for developing this project:

• AWS IoT
  • Device Registry
  • Device Shadows
• AWS Lambda
• Amazon Alexa Custom Skill
• Python

At high level, following are the sequence of events which take place during this interaction:

1. User invokes the Alexa skill (in our case drone pilot) and issues a voice command
2. Alexa skill validates this command with the available set of intents associated to the skill
3. Alexa then sends the identified intent to the configured AWS Lambda function endpoint
4. The lambda function receives incoming command,
   • Queries the device shadow service to check if the drone is online
   • Creates the command message and sends it to the AWS IoT device via MQTT channel
   • Responds to the Alexa command with a success/failure message
5. A Raspberry Pi zero (connected to the DJI Tello via WIFI)
   • Subscribes to the AWS IoT MQTT channel for new messages.
   • On regular intervals, keeps on reporting the drone telemetry like speed, battery status, wifi strength to the AWS IoT device shadow
6. Upon receiving a message, the the Raspberry Pi interprets the MQTT message and issues a corresponding DJI Tello specific command

• Raspberry Pi Zero W or any Raspberry Pi with WIFI on-board
• DJI Tello. Ensure your Tello is setup and you are able to fly with your phone app.
• WiFi Dongle
• If you are using Raspberry Pi Zero W: Micro USB to USB Type A female adapter something like this
• AWS Account. You can create one for free here
• Amazon Alexa Developer account. You can create one for free here
• Amazon Alexa Device or Alexa App (get it from app store or google play) installed on your phone.

Note: Ensure you sign in into the Alexa app from the same email address you used for creating Amazon Alexa Developer account. If you are using Alexa device, then the device should be configured with the same email address.

You can follow the steps mentioned in the hardware section of my previous project to also prepare for the upcoming projects.

Alternatively, to keep it very simple here just connect the Micro USB to USB Type A female adapter + Wifi dongle to the Raspberry Pi (Zero).

• Let's start by download this Repository on your development machine
  git clone https://github.com/erviveksoni/alexa-controlled-drone
• cd into the alexa-controlled-drone directory
• Create a new folder certs

Let's start by setting up a device in AWS IoT to enable us communication with Raspberry Pi.

• Sign in into the AWS Console
• In the find service section, search for the service IoT Core
• On the left hand navigation, click to expand Secure and then select Policies
• Click Create in the top right corner of the screen
• In the create policy screen, click Advanced mode
• Provide a policy name e.g. AlexaPolicy
• In the below JSON. replace the <REGION> with your AWS account region, <ACCOUNT_NUMBER> with your AWS Account Id and <THING_NAME> with the name of the AWS thing you will create e.g. Tello

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "iot:Publish"
      ],
      "Resource": [
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/$aws/things/<THING_NAME>/shadow/update",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/$aws/things/<THING_NAME>/shadow/get",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/takeoff",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/land",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/direction",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/rotate",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/flip"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Receive"
      ],
      "Resource": [
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/$aws/things/<THING_NAME>/shadow/get/accepted",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/$aws/things/<THING_NAME>/shadow/get/rejected",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/$aws/things/<THING_NAME>/shadow/update/accepted",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/$aws/things/<THING_NAME>/shadow/update/rejected",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/takeoff",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/land",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/direction",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/rotate",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topic/drone/flip"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Subscribe"
      ],
      "Resource": [
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topicfilter/$aws/things/<THING_NAME>/shadow/get/accepted",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topicfilter/$aws/things/<THING_NAME>/shadow/get/rejected",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topicfilter/$aws/things/<THING_NAME>/shadow/update/accepted",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topicfilter/$aws/things/<THING_NAME>/shadow/update/rejected",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topicfilter/drone/takeoff",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topicfilter/drone/land",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topicfilter/drone/direction",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topicfilter/drone/rotate",
        "arn:aws:iot:<REGION>:<ACCOUNT_NUMBER>:topicfilter/drone/flip"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "iot:Connect"
      ],
      "Resource": "*"
    }
  ]
}

• Paste the policy text into the text box and click Create

• On the left hand navigation, click to expand Manage and then select Thing
• Click Create in the top right corner of the screen
• Click Create a single thing button in the next screen
• Provide a name for the things e.g.Tello. This should be the same name as used during policy creation
• Click Next
• Click Create certificate in front of One-click certificate creation (recommended)
• Download all the 3 certificate files for your thing (public, private and certificate) and save them into certs folder
• Click Active button to activate the root CA for AWS IoT
• Download the root CA certificate for AWS IoT from here and save it into certs folder
• Click Attach a policy button and select the policy AlexaPolicy you created in the above section
• Click Register thing to finish Thing creation
• Once the Thing is created, open the thing details and click Interact in the left hand navigation
• Make a note of the value of REST API Endpoint under the HTTPS section for later use. e.g. xxxxxxxxxxxxxx-ats.iot.us-east-2.amazonaws.com We will use this endpoint to interact with the Thing later in the process.

At this point, we have all the stuff ready to communicate with the Thing.

Next step is to create an AWS Lambda function which will be invoked by the Alexa skill. The message passed by the Alexa invocation to the Lambda function will be validated against a list of allowed actions and further sent to the Thing we created in the above step.

Every message passed to the Lambda function represents a type of action the user wants to execute. Further every action has a designated MQTT topic defined in the policy attached to the Thing.

• In the AWS developer console, search for lambda
• Click Lambda in the results to navigate to the Lambda console
• Click Create function in the top right corner of the screen
• Put the function name as Alexafunction
• Runs time as Python 3.7
• Click Create function
• In the Designer section, click Add trigger
• In the Trigger configuration page, select Alexa Skill Kit
• Select disable option for the Skill ID verification
• Click Add to complete adding an alexa trigger
• On the Designer section, click the lamda function icon
• Go to Basic settings section of the page
• On a safer side, set memory as 256 MB and Timeout as 10 seconds
• Click Save button on the top right corner to save changes
• Make a note of the lambda function ARN from the top right corner of the screen

• Copy the certs folder in the root of the alexa-controlled-drone directory to the lambda_function subdirectory
• cd into the lambda_function sub directory
• Open lambda_function.py file in your preferred text editor
• Update the config section at the top of this file with the cert names and Rest API Endpoint details you noted earlier Also, replace the <THING_NAME> with the Thing you created in above section

config = { 
         'host': '<REST API Endpoint>',
         'rootCAName': '<Root certificate file name>',
         'certificateName': '<Certificate file name>',
         'privateKeyName' : '<Private key file name>',
         'clientId': 'drone_alexa',
         'port' : 8883
}

thing_name = "<THING_NAME>"

• Save changes and close the file

• Open command line and type pip3 install AWSIoTPythonSDK -t . to download AWSIoTPythonSDK inside the lambda_function directory

• Create a zip package with only the contents of the lambda_function directory

  zip -9r lambda.zip AWSIoTPythonSDK* certs/* iot_client.py lambda_function.py alexa_response_builder.py

• At this point you should have a zip file lambda.zip ready to be uploaded to AWS Lambda function

• Back on the Lambda function console, from the Designer section, click the lamda function icon
• Expand the Code entry type dropdown and select Upload a .zip file
• Click Upload button and browse and select the lambda.zip file
• Click Save button on the top right corner to save changes

You should now be able to see your code in the online code editor interface of AWS Lambda.

Now we are all set to create an Alexa skill which will interact with user to receive commands and fly the drone.

• Sign into Alexa Skills Kit Developer Console with your credential created in prerequisite section
• Click Create Skill button
• Give your skill a name e.g. Tello Voice Control
• Select a default language. Your skill will only appear if the user has this language selected
• Select the model as Custom and hosting method as Provision your own
• Click Create skill button on top right of the screen
• Select the skill template as Start from scratch and then click Choose
• Click Invocation from the left hand navigation
• Specify a Skill Invocation Name e.g. drone pilot
• Click Save Model button at the top of the page
• Click JSON Editor on the left hand navigation
• Copy and paste the contents of the skill.json file you downloaded as part of this repository into the editor surface
• Click Save Model button at the top of the page
• Feel free to go through the list of intents from the left hand navigation. Every intent represents a command the user can invoke
• Click Endpoint from the left hand navigation
• Select AWS Lambda ARN
• In the Default Region textbox paste the ARN of the Lambda function you noted in the previous section
• Click Save Endpoints button at the top of the page
• Click Invocation from the left hand navigation
• Click Build Model button at the top of the page and wait for the skill build process to complete

Now is the time to put your skill to test!!!

There are multiple ways to test your skill. The easiest one is by using the Alexa simulator provided in the Alexa Skills Developer Console

• On the top navigation bar, click Test
• Select Skill testing is enabled in: as Development
• Press the microphone button an speak Alexa, open drone pilot
• You should receive a voice feedback as To start, you should say: Alexa, ask drone pilot to take off.
• You can try other commands e.g. Alexa, ask drone pilot to take off and alexa should respond back with the command acknowledgement

• Sign in to https://alexa.amazon.com/ with your Alexa developer account credentials
• Navigate to Skills section in the left hand navigation
• Click Your Skills on top left of the screen
• Click Dev Skills on top navigation
• Click your skill name e.g. Tello Voice Control
• Click ENABLE button

This will enable your skill on all devices, iOS and Android apps connected to your Alexa developer account.

Congratulations!! You have successfully created an alexa skill to fly your drone!!

Now the last step is to setup Raspberry Pi and make it to talk to AWS IoT thing to receive commands.

We will setup Raspberry Pi in headless mode to get the optimal usage of RAM and CPU. There are many good posts on how to setup Raspbian Buster Lite on the Raspberry Pi Zero in Headless Mode

At this point in time, we should be able to SSH into out Pi using the Wifi onboard. Also the Pi will be most likely have access to the internet (dependeing on your WIFI network settings).

When you turn on Tello, it configures itself as an AP allowing the clients to connect and control to it. Once a client is connected to Tello, it looses internet connectivity. To avoid this we'll configure the Raspberry Pi with dual WIFI interfaces.

The Raspberry Pi onboard WIFI connects to the internet (via my home network) and the WIFI Adapter connects to Tello's WIFI.

Here are the steps:

• Ensure the WIFI dongle is connected to the Raspberry Pi Zero micro usb port
• Power on Raspberry Pi
• SSH into Raspberry Pi Zero
• Type lsusb. Ensure you see the WIFI USB adapter listed on the console output
• Type sudo nano /etc/network/interfaces to edit the network interfaces file
• Add the text below towards the end of the file. Replace the TELLO_NETWORK_NAME with the WIFI AP name of Tello followed by its password.

auto lo

iface lo inet loopback
iface eth0 inet dhcp

allow-hotplug wlan0
iface wlan0 inet manual
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf

allow-hotplug wlan1
iface wlan1 inet dhcp
wpa-ssid "<TELLO_NETWORK_NAME>"
wpa-psk "<PASSWORD>"

iface default inet dhcp

• Save your changes to the interfaces file
• Shutdown Raspberry Pi sudo shutdown now
• Turn on Tello
• Power on Raspberry Pi and SSH into it
• Type ifconfig to list the Raspberry Pi network interfaces
• You should see 2 interfaces wlan0 and wlan1 connected to their network respectively
• In case you don't see an IP address acquired for wlan1, then reset the wlan1 interface using the command sudo dhclient -v wlan1

SSH into Raspberry Pi and follow the steps below.

• sudo apt-get install python3-dev
• sudo apt install python3-pip

• pip3 install AWSIoTPythonSDK
• pip3 install cpython

• git clone https://github.com/hanyazou/TelloPy
• cd TelloPy
• python3 setup.py bdist_wheel
• pip3 install dist/tellopy-*.dev*.whl --upgrade

• Clone this Repository on Raspberry Pi git clone https://github.com/erviveksoni/alexa-controlled-drone
• cd into the alexa-controlled-drone/pi-alexa-code directory
• Copy the certs folder which has all the certificates from your development machine into pi-alexa-code
• Open start.py file in your preferred text editor
• Update the config section at the top of this file with the cert names and Rest API Endpoint details you noted earlier Also, replace the <THING_NAME> with the Thing you created in above section

config = { 
         'host': '<REST API Endpoint>',
         'rootCAName': '<Root certificate file name>',
         'certificateName': '<Certificate file name>',
         'privateKeyName' : '<Private key file name>',
         'clientId': 'drone_alexa_client',
         'port' : 8883
}

thing_name = "<THING_NAME>"

• Save changes and close the file

Now its time to run the application!

• SSH into Raspberry Pi
• Ensure that the drone is powered on and your Raspberry Pi is connected to it's WIFI network using the secondary WLAN interface. Check the Connecting Raspberry Pi to Tello section to verify and troubleshoot.
• cd into the alexa-controlled-drone/pi-alexa-code directory
• Type python3 start.py
• You should see the drone telemetry getting displayed on the console
• Now open your Alexa app or Alexa device with your skill enabled on it
• Say a command from the list below..

Alexa, open drone pilot.
Alexa, ask drone pilot connection status.
Alexa, ask drone pilot status of battery. Other possible values (wifi/battery/camera)
Alexa, ask drone pilot to take off.
Alexa, ask drone pilot to go left. Other possible values (up/down/back/forward/left/right)
Alexa, ask drone pilot to rotate left. Other possible values (left/right)
Alexa, ask drone pilot to flip.
Alexa, ask drone pilot to land.