IoT-For-Beginners/6-consumer/lessons/3-spoken-feedback/single-board-computer-set-timer.md

Set a timer - Virtual IoT Hardware and Raspberry Pi

In this part of the lesson, you will set a timer on your virtual IoT device or Raspberry Pi based off a command from the IoT Hub.

Set a timer

The command sent from the serverless function contains the time for the timer in seconds as the payload. This time can be used to set a timer.

Timers can be set using the Python threading.Timer class. This class takes a delay time and a function, and after the delay time, the function is executed.

Task - set a timer

1. Open the smart-timer project in VS Code, and ensure the virtual environment is loaded in the terminal if you are using a virtual IoT device.

2. Add the following import statement at the top of the file to import the threading Python library:

   import threading
   

3. Above the handle_method_request function that handles the method request, add a function to speak a response. Fow now this will just write to the console, but later in this lesson this will speak the text.

   def say(text):
       print(text)
   

4. Below this add a function that will be called by a timer to announce that the timer is complete:

   def announce_timer(minutes, seconds):
       announcement = 'Times up on your '
       if minutes > 0:
           announcement += f'{minutes} minute '
       if seconds > 0:
           announcement += f'{seconds} second '
       announcement += 'timer.'
       say(announcement)
   

   This function takes the number of minutes and seconds for the timer, and builds a sentence to say that the timer is complete. It will check the number of minutes and seconds, and only include each time unit if it has a number. For example, if the number of minutes is 0 then only seconds are included in the message. This sentence is then sent to the say function.

5. Below this, add the following create_timer function to create a timer:

   def create_timer(seconds):
       minutes, seconds = divmod(seconds, 60)
       threading.Timer(seconds, announce_timer, args=[minutes, seconds]).start()
   

   This function takes the total number of seconds for the timer that will be sent in the command, and converts this to minutes and seconds. It then creates and starts a timer object using the total number of seconds, passing in the announce_timer function and a list containing the minutes and seconds. When the timer elapses, it will call the announce_timer function, and pass the contents of this list as the parameters - so the first item in the list gets passes as the minutes parameter, and the second item as the seconds parameter.

6. To the end of the create_timer function, add some code to build a message to be spoken to the user to announce that the timer is starting:

   announcement = ''
   if minutes > 0:
       announcement += f'{minutes} minute '
   if seconds > 0:
       announcement += f'{seconds} second '    
   announcement += 'timer started.'
   say(announcement)
   

   Again, this only includes the time unit that has a value. This sentence is then sent to the say function.

7. At the start of the handle_method_request function, add the following code to check that the set-timer direct method was requested:

   if request.name == 'set-timer':
   

8. Inside this if statement, extract the timer time in seconds from the payload and use this to create a timer:

   payload = json.loads(request.payload)
   seconds = payload['seconds']
   if seconds > 0:
       create_timer(payload['seconds'])
   

   The timer is only created if the number of seconds is greater than 0

9. Run the app, and ensure the function app is also running. Set some timers, and the output will show the timer being set, and then will show when it elapses:

   pi@raspberrypi:~/smart-timer $ python3 app.py 
   Connecting
   Connected
   Set a one minute 4 second timer.
   1 minute 4 second timer started.
   Times up on your 1 minute 4 second timer.
   

💁 You can find this code in the code-timer/pi or code-timer/virtual-iot-device folder.

😀 Your timer program was a success!