Device shadow (digital twin) in IOT Protocols - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update the device shadow state with the reported temperature.

IOT Protocols

shadow_update = {"state": {"reported": {"temperature": [1]

Drag options to blanks, or click blank then click option'

A"22"

Btemperature

Ctemp

D22

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the number, making it a string instead of a number.

The reported temperature value should be a number, so use 22 without quotes.

2fill in blank

medium

Complete the code to retrieve the desired state from the device shadow JSON.

IOT Protocols

desired_state = shadow_document["state"][[1]]

Drag options to blanks, or click blank then click option'

A"reported"

B"desired"

C"current"

D"status"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reported' instead of 'desired' key.

To get the desired state, access the "desired" key inside the "state" object.

3fill in blank

hard

Fix the error in the code to correctly publish the shadow update to the MQTT topic.

IOT Protocols

mqtt_client.publish("$aws/things/[1]/shadow/update", json.dumps(shadow_update))

Drag options to blanks, or click blank then click option'

Athing_name

Bdevice-name

CthingName

Ddevice_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect variable names that don't match the thing name.

The MQTT topic requires the thing name, which is usually stored in 'thing_name' variable.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that filters reported states with temperature above 25.

IOT Protocols

{k: v for k, v in shadow_state[[1]].items() if v [2] 25}

Drag options to blanks, or click blank then click option'

A"reported"

B>

C<

D"desired"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'desired' instead of 'reported'.

Using '<' instead of '>'.

We want to filter the 'reported' states where the value is greater than 25.

5fill in blank

hard

Fill all three blanks to create a shadow update payload with desired humidity set to 60 and reported temperature unchanged.

IOT Protocols

shadow_payload = {"state": {"desired": {"humidity": [1], "reported": {"temperature": [2], "clientToken": [3]

Drag options to blanks, or click blank then click option'

A60

Bcurrent_temp

C"token123"

D"60"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string '60' instead of number 60.

Using wrong variable for temperature.

Missing quotes around clientToken string.

The desired humidity is 60 (number), temperature uses current_temp variable, and clientToken is a string token.

Practice

1. What is the main purpose of a device shadow in IoT?

easy

A. To keep a virtual copy of a device's state for synchronization

B. To physically store device hardware components

C. To replace the device's firmware remotely

D. To encrypt device communication data

Solution

1. Step 1: Understand device shadow concept

   A device shadow is a virtual representation of a device's state, not a physical component or firmware.

2. Step 2: Identify its main use

   It stores desired and reported states to keep device and cloud synchronized, especially when devices are offline.

3. Final Answer:

   To keep a virtual copy of a device's state for synchronization -> Option A

4. Quick Check:

   Device shadow = virtual state copy [OK]

Hint: Device shadow = virtual device state copy [OK]

Common Mistakes:

• Confusing device shadow with physical device hardware
• Thinking device shadow replaces device firmware
• Assuming device shadow encrypts data

2. Which JSON field in a device shadow document holds the desired state of the device?

easy

A. "reported"

B. "desired"

C. "metadata"

D. "version"

Solution

1. Step 1: Recall device shadow JSON structure

   The device shadow JSON has fields like "desired" and "reported" to represent states.

2. Step 2: Identify desired state field

   The "desired" field contains the state the cloud wants the device to have.

3. Final Answer:

   "desired" -> Option B

4. Quick Check:

   Desired state = "desired" field [OK]

Hint: "desired" field stores target device state [OK]

Common Mistakes:

• Mixing up "reported" and "desired" fields
• Confusing "metadata" with state data
• Thinking "version" holds state info

3. Given this device shadow snippet:

{"state": {"desired": {"power": "on"}, "reported": {"power": "off"}}}

What will the device shadow report after the device updates its state to match the desired power?

medium

A. {"state": {"desired": {"power": "off"}, "reported": {"power": "off"}}}

B. {"state": {"desired": {"power": "on"}, "reported": {"power": "off"}}}

C. {"state": {"desired": {"power": "on"}, "reported": {"power": "on"}}}

D. {"state": {"desired": {}, "reported": {"power": "on"}}}

Solution

1. Step 1: Understand initial shadow states

   The desired state requests power "on"; the reported state shows power "off" initially.

2. Step 2: Update reported state after device changes

   When the device matches the desired state, the reported state updates to "power": "on".

3. Final Answer:

   {"state": {"desired": {"power": "on"}, "reported": {"power": "on"}}} -> Option C

4. Quick Check:

   Reported state matches desired after update [OK]

Hint: Reported state updates to match desired after device sync [OK]

Common Mistakes:

• Assuming desired state changes after device update
• Leaving reported state unchanged
• Removing desired state incorrectly

4. You receive this device shadow update error:

{"error": "Invalid JSON format"}

Which of these shadow update requests is causing the error?

medium

A. {"state": {"desired": {"temperature": 22}}}

B. {"state": {"desired": {"temperature": 22}, "reported": {"temperature": 22}}}

C. {"version": 1, "state": {"desired": {"temperature": 22}, "reported": {"temperature": 22}}}

D. {"state": {"desired": {"temperature": 22}, "reported": {"temperature": 22}"}}

Solution

1. Step 1: Check JSON syntax of each option

   {"state": {"desired": {"temperature": 22}, "reported": {"temperature": 22}"}} has an extra double quote after the reported object closing brace, breaking JSON format.

2. Step 2: Identify invalid JSON causing error

   Invalid JSON causes the "Invalid JSON format" error in device shadow update.

3. Final Answer:

   {"state": {"desired": {"temperature": 22}, "reported": {"temperature": 22}"}} -> Option D

4. Quick Check:

   Invalid JSON syntax = error [OK]

Hint: Look for extra or missing quotes/braces in JSON [OK]

Common Mistakes:

• Overlooking extra quotes or commas
• Confusing valid JSON with similar invalid syntax
• Assuming error is from device, not JSON format

5. You want to ensure a device shadow only updates the reported state if the device is online. Which approach best achieves this?

hard

A. Use a device shadow update callback to confirm device state before updating reported state

B. Delete the device shadow when device is offline

C. Update reported state immediately on cloud request without device confirmation

D. Set desired state to null when device is offline

Solution

1. Step 1: Understand device shadow update flow

   Reported state should reflect actual device state, so cloud must confirm device is online and updated.

2. Step 2: Choose method to confirm device state

   Using a callback or acknowledgment from the device before updating reported state ensures accuracy.

3. Final Answer:

   Use a device shadow update callback to confirm device state before updating reported state -> Option A

4. Quick Check:

   Confirm device state before reported update [OK]

Hint: Confirm device state via callback before updating reported [OK]

Common Mistakes:

• Updating reported state without device confirmation
• Deleting shadow causing loss of state info
• Setting desired state to null instead of managing reported