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130 lines
5.9 KiB
130 lines
5.9 KiB
# Measure temperature - Wio Terminal
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In this part of the lesson, you will add a temperature sensor to your Wio Terminal, and read temperature values from it.
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## Hardware
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The Wio Terminal needs a temperature sensor.
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The sensor you'll use is a [DHT11 humidity and temperature sensor](https://www.seeedstudio.com/Grove-Temperature-Humidity-Sensor-DHT11.html), combining 2 sensors in one package. This is fairly popular, with a number of commercially available sensors combining temperature, humidity and sometimes atmospheric pressure. The temperature sensor component is a negative temperature coefficient (NTC) thermistor, a thermistor where the resistance decreases as the temperature increases.
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This is a digital sensor, so has an onboard ADC to create a digital signal containing the temperature and humidity data that the microcontroller can read.
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### Connect the temperature sensor
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The Grove temperature sensor can be connected to the Wio Terminals digital port.
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#### Task - connect the temperature sensor
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Connect the temperature sensor.
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1. Insert one end of a Grove cable into the socket on the humidity and temperature 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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## Program the temperature sensor
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The Wio Terminal can now be programmed to use the attached temperature sensor.
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### Task program the temperature 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 `temperature-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. Add a library dependency for the Seeed Grove Humidity and Temperature sensor library to the projects `platformio.ini` file:
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```ini
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lib_deps =
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seeed-studio/Grove Temperature And Humidity Sensor @ 1.0.1
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```
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> ⚠️ You can refer to [the instructions for adding libraries to a PlatformIO project in project 1, lesson 4 if needed](../../../1-getting-started/lessons/4-connect-internet/wio-terminal-mqtt.md#install-the-wifi-and-mqtt-arduino-libraries).
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1. Add the following `#include` directives to the top of the file, under the existing `#include <Arduino.h>`:
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```cpp
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#include <DHT.h>
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#include <SPI.h>
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```
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This imports files needed to interact with the sensor. The `DHT.h` header file contains the code for the sensor itself, and adding the `SPI.h` header ensures the code needed to talk to the sensor is linked in when the app is compiled.
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1. Before the`setup` function, declare the DHT sensor:
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```cpp
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DHT dht(D0, DHT11);
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```
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This declares an instance of the `DHT` class that manages the **D**igital **H**umidity and **T**emperature sensor. This is connected to port `D0`, the right-hand-side Grove socket on the Wio Terminal. The second parameter tells the code the sensor being used is the *DHT11* sensor - the library you are using supports other variants of this sensor.
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1. In the `setup` function, add code to set up the serial connection:
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```cpp
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void setup()
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{
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Serial.begin(9600);
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while (!Serial)
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; // Wait for Serial to be ready
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delay(1000);
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}
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```
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1. At the end of the `setup` function, after the last `delay`, add a call to start the DHT sensor:
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```cpp
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dht.begin();
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```
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1. In the `loop` function, add code to call the sensor and print the temperature to the serial port:
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```cpp
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void loop()
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{
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float temp_hum_val[2] = {0};
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dht.readTempAndHumidity(temp_hum_val);
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Serial.print("Temperature: ");
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Serial.print(temp_hum_val[1]);
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Serial.println ("°C");
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delay(10000);
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}
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```
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This code declares an empty array of 2 floats, and passes this to the call to `readTempAndHumidity` on the `DHT` instance. This call populates the array with 2 values - the humidity goes in the 0th item in the array (remember in C++ arrays are 0-based, so the 0th item is the 'first' item in the array), and the temperature goes into the 1st item.
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The temperature is read from the 1st item in the array, and printed to the serial port.
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> 🇺🇸 The temperature is read in Celsius. For Americans, to convert this to Fahrenheit, divide the Celsius value read by 5, then multiply by 9, then add 32. For example, a temperature reading of 20°C becomes ((20/5)*9) + 32 = 68°F.
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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 temperature using the serial monitor:
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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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Temperature: 25.00°C
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Temperature: 25.00°C
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Temperature: 25.00°C
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Temperature: 24.00°C
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```
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> 💁 You can find this code in the [code-temperature/wio-terminal](code-temperature/wio-terminal) folder.
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😀 Your temperature sensor program was a success!
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