Grove Temp&Humi Sensor (SHT40)
In this section, we will detail how the sensors work, how to get sensor data using Wio Terminal and how to send the data out using Wio Terminal & Grove - Wio-E5.
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Working Principle of Sensors
The SHT40 temperature is measured using a thermocouple method. A thermocouple consists of two types of metallic wires of different materials. One end of the two wires is welded together to form the working end, which is placed at the temperature to be measured. The other end is called the free end and is connected to the main control to form a closed loop. When the temperature of the working end and the free end is different, a thermoelectric potential will appear in the loop, and the change in this voltage will be sent to the SCM through conversion of the circuit and transformed into a signal that can be recognized by the machine.
The SHT40 humidity is measured using a polyamine or acetate polymer film (a highly fractionated compound) deposited on two conductive electrodes. When the film absorbs or loses water, it changes the dielectric constant between the two electrodes, which in turn causes a change in capacitor capacity. The change in capacitance can be captured and converted using external measurement circuitry, and eventually displayed as an easily identifiable signal on the output.
For more information on the use of Grove Temp&Humi Sensor its reference here.
Materials Required
 |  |  |
| Wio Terminal | Grove - Wio-E5 | Grove Temp&Humi Sensor (SHT40) |
Preliminary Preparation
Connection
In this routine, we need to connect to a nearby LoRa® gateway with the help of Grove - Wio-E5. We need to configure the Grove port on the right side of the Wio Terminal as a soft serial port to receive AT commands. Grove Temp&Humi Sensor (on the left side) according to the diagram below.
Software preparation
Step 1. You need to Install an Arduino Software.
Step 2. Launch the Arduino application.
Step 3. Add Wio Terminal to the Arduino IDE.
Open your Arduino IDE, click on File > Preferences, and copy below url to Additional Boards Manager URLs:
https://files.seeedstudio.com/arduino/package_seeeduino_boards_index.json
Click on Tools > Board > Board Manager and Search Wio Terminal in the Boards Manager.
Step 4. Select your board and port
You'll need to select the entry in the Tools > Board menu that corresponds to your Arduino. Selecting the Wio Terminal.
Select the serial device of the Wio Terminal board from the Tools -> Port menu. This is likely to be COM3 or higher (COM1 and COM2 are usually reserved for hardware serial ports). To find out, you can disconnect your Wio Terminal board and re-open the menu; the entry that disappears should be the Arduino board. Reconnect the board and select that serial port.
For Mac User, it will be something like /dev/cu.usbmodem141401.
If you are not able to upload the sketch, mostly it's because Arduino IDE was not able to put Wio Terminal to bootloader mode. (Because MCU was halted or your program handling USB) Workaround is putting your Wio Terminal to bootloader mode manually.
Step 5. Download Grove - Wio-E5 Library
Visit the Disk91_LoRaE5 repositories and download the entire repo to your local drive.
Step 6. Adding libraries to the Arduino IDE
Now, the 3-Axis Digital Accelerometer library can be installed to the Arduino IDE. Open the Arduino IDE, and click sketch -> Include Library -> Add .ZIP Library, and choose the Disk91_LoRaE5 file that you've have just downloaded.
Get the value of the Grove Temp&Humi Sensor (SHT40)
Step 1. Download Grove Temp&Humi Sensor Code Library
Visit the arduino-i2c-sht4x repositories and download the entire repo to your local drive.
Visit the Sensirion Arduino Core Library repositories and download the entire repo to your local drive.
Step 2. Adding libraries to the Arduino IDE
Now, the Grove Temp&Humi Sensor library can be installed to the Arduino IDE. Open the Arduino IDE, and click sketch -> Include Library -> Add .ZIP Library, and choose the arduino-i2c-sht4x file that you've have just downloaded.
Step 3. Obtain temperature and humidity data from SHT40
This repo shows us the temperature and humidity data obtained. In the code, we use the measureHighPrecision() function to get the temperature and humidity information, which is positive and float.
#include <Arduino.h>
#include <SensirionI2CSht4x.h>
#include <Wire.h>
SensirionI2CSht4x sht4x;
void setup() {
Serial.begin(115200);
while (!Serial) {
delay(100);
}
Wire.begin();
uint16_t error;
char errorMessage[256];
sht4x.begin(Wire);
uint32_t serialNumber;
error = sht4x.serialNumber(serialNumber);
if (error) {
Serial.print("Error trying to execute serialNumber(): ");
errorToString(error, errorMessage, 256);
Serial.println(errorMessage);
} else {
Serial.print("Serial Number: ");
Serial.println(serialNumber);
}
}
void loop() {
uint16_t error;
char errorMessage[256];
delay(1000);
float temperature;
float humidity;
error = sht4x.measureHighPrecision(temperature, humidity);
if (error) {
Serial.print("Error trying to execute measureHighPrecision(): ");
errorToString(error, errorMessage, 256);
Serial.println(errorMessage);
} else {
Serial.print("Temperature:");
Serial.print(temperature);
Serial.print("\t");
Serial.print("Humidity:");
Serial.println(humidity);
}
}
Open the serial monitor of Arduino IDE and select the baud rate as 115200 and observe the result.
Send data via Grove - Wio-E5
We combine the previous code of Grove - Wio-E5 to connect to the LoRa® network. Using the AT command it is possible to send the value of the Grove Temp&Humi Sensor to the LoRa® network.
In the code in the previous section, we know that the temperature and humidity values are generally a combination of two integers and two decimals, and all are positive, float.
Due to the limitations of sending data, we need to solve the problem of converting float numbers to integers on the sending side to ensure that the data sent is an integer, so we multiply all temperature and humidity values by 100.
In this way, we determine the content, size and format of the data to be sent via the AT command. We might as well set up a large enough array, store the strings we need to send into the array, and finally use the send_sync() function to send the array out.
The pseudo-code for the above idea is roughly as follows.
......
error = sht4x.measureHighPrecision(temperature, humidity);
int_temp = temperature*100;
int_humi = humidity*100;
static uint8_t data[4] = { 0x00 }; //Use the data[] to store the values of the sensors
data_decord(int_temp, int_humi, data);
if ( lorae5.send_sync( //Sending the sensor values out
8, // LoRaWan Port
data, // data array
sizeof(data), // size of the data
false, // we are not expecting a ack
7, // Spread Factor
14 // Tx Power in dBm
)
)
......
The rest of what we need to do is to use the begin() function to initialize Grove - Wio-E5 and the setup() function to configure the triplet information of Grove - Wio-E5. When we send a data message using the send_sync() function, we will try to join the LoRaWAN® at the same time, and once it succeeds, the data will be sent and information such as signal strength and address will be returned.
The full code example can be found here.
We do not recommend that you upload the code now to see the results, because at this point you have not yet configured Helium/TTN and will get a "Join failed" result. We recommend that you upload this code after you have completed the Connecting to Helium or Connecting to TTN chapter to complete the complete data sending process.
Once you have experienced and understood how the Grove Temp&Humi Sensor works and the data format, please continue with the next step of the tutorial join LoRaWAN®.
| Helium Section | |
| Helium Introduction In this chapter, we will introduce the Helium console controls that we use to get a first impression of the Helium console. Jump to chapter > |
| Connecting to Helium This section describes how to configure Helium so that sensor data can be successfully uploaded to and displayed in Helium. Jump to chapter > |
| TTN Section | |
| TTN Introduction In this chapter, we will introduce the TTN console controls that we use to get a first impression of the TTN console. Jump to chapter > |
| Connecting to TTN This section describes how to configure TTN so that sensor data can be successfully uploaded to and displayed in TTN. Jump to chapter > |
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