Bluetooth OLED¶

This project uses an Android app created with MIT App Inventor to send messages over Bluetooth to an Arduino device. The Arduino, upon receiving the messages, displays them on an OLED screen. The Android app, designed with a user-friendly interface, allows users to input messages and send them with the press of a button.

The Android application will be constructed utilizing a complimentary web-based platform known as MIT App Inventor. The project presents an excellent opportunity to gain familiarity with the interfacing of an Arduino with a smartphone.

1. Build the Circuit¶

2. Create the Android App¶

The Android application will be developed using a free web application known as MIT App Inventor. MIT App Inventor serves as an excellent starting point for Android development, owing to its intuitive drag-and-drop features allowing for the creation of simplistic applications.

Now, let’s begin.

Go to Get Started with MIT App Inventor, and click “online tool” to login. You will require a Google account to register with MIT App Inventor.
After logging in, navigate to Projects -> Import project (.aia) from my computer. Subsequently, upload the oled.aia file located in the path ultimate-sensor-kit\iot_project\bluetooth\07-Bluetooth_oled.

You can also directly download here: oled.aia
Upon uploading the .aia file, you will see the application on the MIT App Inventor software. This is a pre-configured template. You can modify this template after you have familiarized yourself with MIT App Inventor through the following steps.
In MIT App Inventor, you have 2 primary sections: the Designer and the Blocks. You can switch between these two sections in the upper right corner of the page.
The Designer allows you to add buttons, text, screens, and modify the overall aesthetic of your application.
Next, there’s the Blocks section. This section lets you craft custom functionalities for your app, allowing you to program each component on the app’s GUI to achieve desired features.
To install the application on a smartphone, navigate to the Build tab.
- You can generate a .apk file. After selecting this option, a page will appear allowing you to choose between downloading a .apk file or scanning a QR code for installation. Follow the installation guide to complete the application installation.
  
  You also download our pre-compiled APK here: piano.apk
- If you wish to upload this app to Google Play or another app marketplace, you can generate a .aab file.

3. Upload the Code¶

Open the 07-Bluetooth_oled.ino file under the path of ultimate-sensor-kit\iot_project\bluetooth\07-Bluetooth_oled, or copy this code into Arduino IDE.

Note

To install the library, use the Arduino Library Manager and search for “Adafruit SSD1306” and “Adafruit GFX” and install it.
After selecting the correct board and port, click the Upload button.
Open the Serial monitor(set baudrate to 9600) to view debug messages.

4. App and Bluetooth module Connection¶

Ensure that the application created earlier is installed on your smartphone.

Initially, turn on Bluetooth on your smartphone.
Navigate to the Bluetooth settings on your smartphone and look for names like JDY-31-SPP.
After clicking it, agree to the Pair request in the pop-up window. If prompted for a pairing code, please enter “1234”.
Now open the newly installed OLED APP.
In the APP, click on Connect button to establish a connection between the APP and Bluetooth module.
This page displays a list of all paired Bluetooth devices. Choose the xx.xx.xx.xx.xx.xx JDY-31-SPP option from the list. The name of each device is listed next to its MAC address.

After a successful connection, the OLED display will switch from showing “Waiting for connection” to displaying the MAC address of the connected device.
If you don’t see any devices on the page shown above, it could be because this app is not authorized to scan for nearby devices. In such a case, you will need to adjust the settings manually.
- To access the APP Info page, long-press the app icon and select it. Alternatively, if you have another method to reach this page, use that instead.
- Navigate to the Permissions page.
- To enable the APP to scan for nearby devices, go to Nearby devices and select Always.
- Now, restart the APP and repeat steps 5 and 6 to successfully connect to Bluetooth.
After a successful connection, you will be redirected to the main page. Enter your desired message in the text box provided and click on the send button to display it on the OLED screen.

5. Code explanation¶

Setting Up Bluetooth Communication:

This section includes the SoftwareSerial library and sets up the digital pins for Bluetooth communication. The standard Serial is for debugging while bleSerial is specifically for Bluetooth communication.
```
#include <SoftwareSerial.h>
const int bluetoothTx = 3;
const int bluetoothRx = 4;
SoftwareSerial bleSerial(bluetoothTx, bluetoothRx);
```

Setting Up OLED Display:

The libraries and constants required to initialize and manage the OLED display are declared here.

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
#define SCREEN_ADDRESS 0x3C
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

Initialization:

In the setup() function, serial communications are initialized. The OLED display is started, and an initial message “Waiting for connection” is displayed.

void setup() {
   Serial.begin(9600);
   bleSerial.begin(9600);
   if (!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {
      Serial.println(F("SSD1306 allocation failed"));
      for (;;)
         ;
   }
   display.clearDisplay();
   display.setTextColor(WHITE);
   display.setTextSize(1);
   display.setCursor(32, 20);
   display.println("Waiting for");
   display.setCursor(32, 30);
   display.println("connection");
   display.display();
}

Main Loop:

Within the loop(), the code constantly checks for incoming data from the Bluetooth module. Once a full message (ending with a ‘#’, the APP will automatically add a ‘#’ at the end of the message that the user send) is received, it’s displayed on the OLED. Also, the received message is printed to the serial monitor for debugging purposes.

void loop() {
   while (bleSerial.available() > 0) {
      character = bleSerial.read();
      message = message + character;
      if (character == '#') {
         message = message.substring(0, message.length() - 1);
         Serial.println();
         Serial.print("DEBUG:");
         Serial.println(message);
         display.clearDisplay();
         display.setTextColor(WHITE);
         display.setTextSize(1);
         display.setCursor(0, 20);
         display.println(message);
         display.display();
         message = "";
         delay(200);
      }
   }
}