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104 lines
4.5 KiB
104 lines
4.5 KiB
# Measure soil moisture - Wio Terminal
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In this part of the lesson, you will add a capacitive soil moisture sensor to your Wio Terminal, and read values from it.
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## Hardware
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The Wio Terminal needs a capacitive soil moisture sensor.
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The sensor you'll use is a [Capacitive Soil Moisture Sensor](https://www.seeedstudio.com/Grove-Capacitive-Moisture-Sensor-Corrosion-Resistant.html), 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.
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This is an analog sensor, so connects to analog pins on the Wio Terminal, using an onboard ADC to create a value from 0-1,023.
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### Connect the soil moisture sensor
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The Grove soil moisture sensor can be connected to the Wio Terminals configurable analog/digital port.
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#### Task - connect the soil moisture sensor
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Connect the soil moisture sensor.
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1. Insert one end of a Grove cable into the socket on the soil moisture sensor. It will only go in one way round.
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1. With the Wio Terminal disconnected from your computer or other power supply, connect the other end of the Grove cable to the right-hand side Grove socket on the Wio Terminal as you look at the screen. This is the socket farthest away from the power button.
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1. Insert the soil moisture sensor into soil. It has a 'highest position line' - a white line across the sensor. Insert the sensor up to but not past this line.
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1. You can now connect the Wio Terminal to your computer.
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## Program the soil moisture sensor
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The Wio Terminal can now be programmed to use the attached soil moisture sensor.
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### Task - program the soil moisture sensor
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Program the device.
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1. Create a brand new Wio Terminal project using PlatformIO. Call this project `soil-moisture-sensor`. Add code in the `setup` function to configure the serial port.
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> ⚠️ You can refer to [the instructions for creating a PlatformIO project in project 1, lesson 1 if needed](../../../1-getting-started/lessons/1-introduction-to-iot/wio-terminal.md#create-a-platformio-project).
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1. There isn't a library for this sensor, instead you can read from the analog pin using the built in Arduino [`analogRead`](https://www.arduino.cc/reference/en/language/functions/analog-io/analogread/) function. Start by configuring the analog pin for input so values can be read from it by adding the following to the `setup` function.
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```cpp
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pinMode(A0, INPUT);
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```
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This sets the `A0` pin, the combined analog/digital pin, as an input pin that voltage can be read from.
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1. Add the following to the `loop` function to read the voltage from this pin:
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```cpp
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int soil_moisture = analogRead(A0);
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```
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1. Below this code, add the following code to print the value to the serial port:
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```cpp
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Serial.print("Soil Moisture: ");
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Serial.println(soil_moisture);
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```
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1. Finally add a delay at the end of 10 seconds:
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```cpp
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delay(10000);
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```
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1. Build and upload the code to the Wio Terminal.
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> ⚠️ You can refer to [the instructions for creating a PlatformIO project in project 1, lesson 1 if needed](../../../1-getting-started/lessons/1-introduction-to-iot/wio-terminal.md#write-the-hello-world-app).
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1. Once uploaded, you can monitor the soil moisture using the serial monitor. Add some water to the soil, or remove the sensor from the soil, and see the value change.
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```output
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> Executing task: platformio device monitor <
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--- Available filters and text transformations: colorize, debug, default, direct, hexlify, log2file, nocontrol, printable, send_on_enter, time
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--- More details at http://bit.ly/pio-monitor-filters
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--- Miniterm on /dev/cu.usbmodem1201 9600,8,N,1 ---
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--- Quit: Ctrl+C | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
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Soil Moisture: 526
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Soil Moisture: 529
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Soil Moisture: 521
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Soil Moisture: 494
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Soil Moisture: 454
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Soil Moisture: 456
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Soil Moisture: 395
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Soil Moisture: 388
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Soil Moisture: 394
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Soil Moisture: 391
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```
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In the example output above, you can see the voltage drop as water is added.
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> 💁 You can find this code in the [code/wio-terminal](code/wio-terminal) folder.
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😀 Your soil moisture sensor program was a success!
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