IoT-For-Beginners/1-getting-started/lessons/3-sensors-and-actuators/virtual-device-actuator.md

# Build a nightlight - Virtual IoT Hardware

In this part of the lesson, you will add an LED to your virtual IoT device and use it to create a nightlight.

## Virtual Hardware

The nightlight needs one actuator, created in the CounterFit app.

The actuator is an **LED**. In a physical IoT device, it would be a [light-emitting diode](https://wikipedia.org/wiki/Light-emitting_diode) that emits light when current flows through it. This is a digital actuator that has 2 states, on and off. Sending a value of 1 turns the LED on, and 0 turns it off.

The nightlight logic in pseudo-code is:

```output
Check the light level.
If the light is less than 200
    Turn the LED on
Otherwise
    Turn the LED off
```

### Add the sensors to CounterFit

To use a virtual LED, you need to add it to the CounterFit app

#### Task

Add the LED to the CounterFit app.

1. Make sure the CounterFit web app is running from the previous part of this assignment. If not, start it and re-add the light sensor.

1. Create an LED:

    1. In the *Create actuator* box in the *Actuator* pane, drop down the *Actuator type* box and select *LED*.

    1. Set the *Pin* to *5*

    1. Select the **Add** button to create the LED on Pin 5

    ![The LED settings](../../../images/counterfit-create-led.png)

    The LED will be created and appear in the actuators list.

    ![The LED created](../../../images/counterfit-led.png)

    Once the LED has been created, you can change the color using the *Color* picker. Select the **Set** button to change the color after you have selected it.

### Program the nightlight

The nightlight can now be programmed using the CounterFit light sensor and LED.

#### Task

Program the nightlight.

1. Open the nightlight project in VS Code that you created in the previous part of this assignment. Kill and re-create the terminal to ensure it is running using the virtual environment if necessary.

1. Open the `app.py` file

1. Add the following code to the `app.py` file to connect to import a required library. This should be added to the top, below the other `import` lines.

    ```python
    from counterfit_shims_grove.grove_led import GroveLed
    ```

    The `from counterfit_shims_grove.grove_led import GroveLed` statement imports the `GroveLed` from the CounterFit Grove shim Python libraries. This library has code to interact with an LED created in the CounterFit app.

1. Add the following code after the `light_sensor` declaration to create an instance of the class that manages the LED:

    ```python
    led = GroveLed(5)
    ```

    The line `led = GroveLed(5)` creates an instance of the `GroveLed` class connecting to pin **5** - the CounterFit Grove pin that the LED is connected to.

1. Add a check inside the `while` loop, and before the `time.sleep` to check the light levels and turn the LED on or off:

    ```python
    if light < 200:
        led.on()
    else:
        led.off()
    ```

    This code checks the `light` value. If this is less than 200 it calls the `on` method of the `GroveLed` class which sends a digital value of 1 to the LED, turning it on. If the light value is greater than or equal to 200 it calls the `off` method, sending a digital value of 0 to the LED, turning it off.

    > 💁 This code should be indented to the same level as the `print('Light level:', light)` line to be inside the while loop!

1. From the VS Code Terminal, run the following to run your Python app:

    ```sh
    python3 app.py
    ```

    You should see light values being output to the console.

    ```output
    (.venv) ➜  GroveTest python3 app.py 
    Light level: 143
    Light level: 244
    Light level: 246
    Light level: 253
    ```

1. Change the *Value* or the *Random* settings to vary the light level above and below 200. You will see the LED turn on and off.

![The LED in the CounterFit app turning on and off as the light level changes](../../../images/virtual-device-running-assignment-1-1.gif)

> 💁 You can find this code in the [code-actuator/virtual-device](code-actuator/virtual-device) folder.

😀 Your nightlight program was a success!