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Build a nightlight - Virtual IoT Hardware

In this part of the lesson, you will add a light sensor to your virtual IoT device.

Virtual Hardware

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

The sensor is a light sensor. In a physical IoT device, it would be a photodiode that converts light to an electrical signal. Light sensors are analog sensors that sends an integer value indicating a relative amount of light, that doesn't map to any standard unit of measurement such as lux.

Add the sensors to CounterFit

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

Task - add the sensors to CounterFit

Add the light sensor to the CounterFit app.

Make sure the CounterFit web app is running from the previous part of this assignment. If not, start it.
Create a light sensor:
1. In the Create sensor box in the Sensors pane, drop down the Sensor type box and select Light.
2. Leave the Units set to NoUnits
3. Ensure the Pin is set to 0
4. Select the Add button to create the light sensor on Pin 0
The light sensor will be created and appear in the sensors list.

Program the light sensor

The device can now be programmed to use the built in light sensor.

Task - program the light sensor

Program the device.

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.
Open the app.py file
Add the following code to the top of app.py file with the rest of the import statements to connect to import some required libraries:
```
import time
from counterfit_shims_grove.grove_light_sensor_v1_2 import GroveLightSensor
```
The import time statement imports the Python time module that will be used later in this assignment.

The from counterfit_shims_grove.grove_light_sensor_v1_2 import GroveLightSensor statement imports the GroveLightSensor from the CounterFit Grove shim Python libraries. This library has code to interact with a light sensor created in the CounterFit app.
Add the following code to the bottom of the file to create instances of classes that manage the light sensor:
```
light_sensor = GroveLightSensor(0)
```
The line light_sensor = GroveLightSensor(0) creates an instance of the GroveLightSensor class connecting to pin 0 - the CounterFit Grove pin that the light sensor is connected to.
Add an infinite loop after the code above to poll the light sensor value and print it to the console:
```
while True:
    light = light_sensor.light
    print('Light level:', light)
```
This will read the current light level using the light property of the GroveLightSensor class. This property reads the analog value from the pin. This value is then printed to the console.
Add a small sleep of one second at the end of the while loop as the light levels don't need to be checked continuously. A sleep reduces the power consumption of the device.
```
time.sleep(1)
```
From the VS Code Terminal, run the following to run your Python app:
```
python3 app.py
```
Light values will be output to the console. Initially this value will be 0.
From the CounterFit app, change the value of the light sensor that will be read by the app. You can do this in one of two ways:
- Enter a number in the Value box for the light sensor, then select the Set button. The number you enter will be the value returned by the sensor.
- Check the Random checkbox, and enter a Min and Max value, then select the Set button. Every time the sensor reads a value, it will read a random number between Min and Max.
The values you set will be output to the console. Change the Value or the Random settings to make the value change.
```
(.venv) ➜  GroveTest python3 app.py 
Light level: 143
Light level: 244
Light level: 246
Light level: 253
```

💁 You can find this code in the code-sensor/virtual-device folder.

😀 Your nightlight program was a success!

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