Working with UART by Using Java ME Embedded and a Raspberry Pi

1. Place the 26-pin header connector into the breadboard so that:

   • The connector straddles the center.
   • Pin 1 (marked 3V3) is in column 14 at the top.
   • The "key" (the square cutout in the center of the connector) is in the center at the top.

   

   Note: Your breadboard may be different. Leave enough room to place the GPS device to the left of the connector.

2. Insert the GPS breakout board into the breadboard so that the breakout board's left pin (PPS) is in row 1.

   

   All of the breakout board's pins should be in column f.

3. Check that you have version 2 of the Raspberry Pi. For more information, see "Checking the Hardware Version of Your Raspberry Pi" in the tutorial titled Working with GPIO by Using Java Embedded and a Raspberry Pi.

4. Perform the following tasks, using the row numbers shown in the image as a reference:

   1. Insert a red wire between row 2, marked VIN on the GPS breakout board, and row 14 on the connector (marked 5v0).
      Note: Because the GPS device has an internal voltage regulator, you can wire it to the 5V output line.
   2. Insert a green wire between row 3, marked GND on the GPS breakout board, and row 16 on the connector (marked GND) .
   3. Insert a blue wire between row 4, marked RX on the GPS breakout board, and row 17 on the connector (marked TXD).
   4. Insert a white wire between row 5, marked TX on the GPS breakout board, and row 18 on the connector (marked RXD).

   

   Note: You are cross-wiring the RX pin on the GPS device to the TXD pin on the connector, and the TX pin on the GPS device to the RXD pin on the connector.

   Your wiring should look similar to this picture:

   

5. Review the application circuit that you created.



Note: It is important that you cross-connect the RX pin on the GPS device to the TXD pin on the connector and the TX pin on the GPS device to the RXD pin on the connector.

6. Unplug the Raspberry Pi power cable .

7. Connect the ribbon cable between the breadboard and the Raspberry Pi.

   If you have not performed this step before, see "Connecting the Ribbon Cable Between the Raspberry Pi and the Header" in the tutorial titled Working with GPIO by Using Java Embedded and a Raspberry Pi.

8. Plug the power cable back into your Raspberry Pi.

1. Connect to the Raspberry Pi by using PuTTY.

   

2. Enter sudo nano /boot/cmdline.txt.

   

3. Remove console=ttyAMA0,115200 kgdboc=ttyAMA0,115200 from the first line in the file.

   

4. Press Ctrl + O and Enter, and then press Ctrl + X to write and close the file.

   

5. Enter sudo nano /etc/inittab.

   

6. Perform the following steps:

   1. Comment out the last line (enter a # at the beginning of the line).
   2. Press Ctrl + O and Enter to write the file.
   3. Press Ctrl + X to close the file.

   

   At this point, you have released the /dev/ttyAMA0 UART serial port.

7. Enter sudo reboot to reboot the Raspberry Pi and make the changes.

   

8. After a few minutes, right-click in the PuTTY window and select Restart Session to reconnect to the Raspberry Pi.

   

9. Log in with the user id pi and the password raspberry.

   

10. Enter sudo gpsd /dev/ttyAMA0 -F /var/run/gpsd.sock to start the gpsd daemon on the UART serial port (/dev/ttyAMA0).

    

11. Enter cgps -s to display the GPS data.

    

    Formatted data from the GPS device is displayed in the console window.

    

    The GPS device is writing correctly to the UART connection.

1. Select File > New Project.

   

2. Select Java ME Embedded from Categories and Java ME Embedded Application from Projects and click Next.

   

3. In the New Java ME Embedded Application dialog, perform the following steps:
   

   1. Enter GPSExample as the Project name.
   2. Select EmbeddedExternalDevice1 as the Java ME Platform.
   3. Enter com.example.GPSIMlet in the Create Midlet field.
   4. Click Finish.

   

Java ME Embedded projects that use UART and Comm devices must set special API permissions.

1. Right click the Project and select Properties.

   

2. Click the Application Descriptor category and select to the API Permissions tab. Click Add.

   

3. In the Add Permission dialog:

   1. Select jdk.dio.DeviceMgmtPermission from the drop-down menu list.
   2. Enter *:* as the protected resource name.
   3. Enter open in the Actions Requested field.
   4. Click OK.

   

4. Click Add to add another permission for a UART connection.

   

5. In the Add Permission dialog:

   1. Select jdk.dio.uart.UARTPermission from the drop-down menu.
   2. Enter *:* as the protected resource name.
   3. Click OK.

   

6. Click Add to add another permission for a Comm Connection.

   

7. In the Add Permission dialog:

   1. Select javax.microedition.io.CommProtocolPermission from the drop-down menu.
   2. Enter comm:* as the protected resource name.
   3. Click OK.

   

8. Click Ok to close the properties dialog.

   

1. Expand the classes.zip file provided in the Resources section.

2. Copy the files GPSCommSensor.java, GPSSensor.java, GPSUARTSensor.java, Position.java.

3. In NetBeans, right-click on the com.example package and select Paste to paste the files into the project.

   

   There should be five files in the com.example package.

   

4. Open the GPSSensor class and note that it is an abstract class. This class provides the base functionality for the GPS sensor, but must be implemented by another class to be instantiated.

5. Open the GPSUARTSensor and GPSCommSensor classes. These classes provide the specific protocol support for the sensor, as a comm-port device or UART device respectively.

6. Open the Position class. Note that this class is a POJO, but provides a valuable method for converting the NMEA strings to degree/minute/second position values.

1. Add the following class field:

   
       private static final String SERIAL_PORT = "ttyAMA0";
   
   

2. Implement the startApp method.

   
       @Override
       public void startApp() {
           try (GPSUARTSensor gps = new GPSUARTSensor())  {
           //try (GPSCommSensor gps = new GPSCommSensor(SERIAL_PORT)) {
   
               /* Take one reading every second for 10 readings */
               for (int i = 0; i < 10; i++) {
                   Position p = gps.getPosition();
                   // Use the toString method to print the result
                   System.out.println(p + "\n");
                   Thread.sleep(1000);
               }
           } catch (IOException ioe) {
               System.out.println("GPSTestMidlet: IOException " + ioe.getMessage());
           } catch (InterruptedException ex) {
               // Ignore
           }
   
           /* Terminate the Imlet correctly */
           System.out.println("GPSTestMidlet finished");
           notifyDestroyed();
       }
   

   This method creates an instance of GPSUARTSensor object in a try-with-resources block. When the try ends, the close method will automatically get called, obviating the need for the destroyApp method.

3. Fix any missing import statements and save the file.