virtual-device-soil-moisture.md

Measure soil moisture - Virtual IoT Hardware

In this part of the lesson, you will add a capacitive soil moisture sensor to your virtual IoT device, and read values from it.

Virtual Hardware

The virtual IoT device will use a simulated Grove capacitive soil moisture sensor. This keeps this lab the same as using a Raspberry Pi with a physical Grove capacitive soil moisture sensor.

In a physical IoT device, the soil moisture sensor would be a capacitive sensor that measures soil moisture by detecting the capacitance of the soil, a property than changes as the soil moisture changes. As the soil moisture increases, the voltage decreases.

This is an analog sensor, so uses a simulated 10-bit ADC to report a value from 1-1,023.

Add the soil moisture sensor to CounterFit

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

Task - Add the soil moisture sensor to CounterFit

Add the soil moisture sensor to the CounterFit app.

1. Create a new Python app on your computer in a folder called soil-moisture-sensor with a single file called app.py and a Python virtual environment, and add the CounterFit pip packages.

   ⚠️ You can refer to the instructions for creating and setting up a CounterFit Python project in lesson 1 if needed.

2. Make sure the CounterFit web app is running

3. Create a soil moisture sensor:

   1. In the Create sensor box in the Sensors pane, drop down the Sensor type box and select Soil Moisture.

   2. Leave the Units set to NoUnits

   3. Ensure the Pin is set to 0

   4. Select the Add button to create the Soil Moisture sensor on Pin 0

   

   The soil moisture sensor will be created and appear in the sensors list.

   

Program the soil moisture sensor app

The soil moisture sensor app can now be programmed using the CounterFit sensors.

Task - program the soil moisture sensor app

Program the soil moisture sensor app.

1. Make sure the soil-moisture-sensor app is open in VS Code

2. Open the app.py file

3. Add the following code to the top of app.py to connect the app to CounterFit:

   from counterfit_connection import CounterFitConnection
   CounterFitConnection.init('127.0.0.1', 5000)

4. Add the following code to the app.py file to import some required libraries:

   import time
   from counterfit_shims_grove.adc import ADC

   The import time statement imports the time module that will be used later in this assignment.

   The from counterfit_shims_grove.adc import ADC statement imports the ADC class to interact with a virtual analog to digital converter that can connect to a CounterFit sensor.

5. Add the following code below this to create an instance of the ADC class:

   adc = ADC()

6. Add an infinite loop that reads from this ADC on pin 0 and write the result to the console. This loop can then sleep for 10 seconds between reads.

   while True:
       soil_moisture = adc.read(0)
       print("Soil moisture:", soil_moisture)
   
       time.sleep(10)

7. From the CounterFit app, change the value of the soil moisture 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 soil moisture 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.

8. Run the Python app. You will see the soil moisture measurements written to the console. Change the Value or the Random settings to see the value change.

   (.venv) ➜ soil-moisture-sensor $ python app.py 
   Soil moisture: 615
   Soil moisture: 612
   Soil moisture: 498
   Soil moisture: 493
   Soil moisture: 490
   Soil Moisture: 388
   

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

😀 Your soil moisture sensor program was a success!