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.

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

    ```python
    import threading
    ```

1. 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.

    ```python
    def say(text):
        print(text)
    ```

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

    ```python
    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.

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

    ```python
    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.

1. 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:

    ```python
    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.

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

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

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

    ```python
    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

1. 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:

    ```output
    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](code-timer/pi) or [code-timer/virtual-iot-device](code-timer/virtual-iot-device) folder.

😀 Your timer program was a success!