Android Communication: Use of COM Port for Data Transfer

Android Communication: Use of COM Port for Data Transfer | Magora Systems

A few months ago I was asked to develop a dashboard for Android which could display electricity network data in a workshop. The main problem was that the device that collects the data stands alone and must be connected to an Android device via a serial port. In this article, I will explore the possibility using a COM port in applications for an Android OS. It is needed when your application must receive/send data from the other device that only has RS 232 serial port as a means of communication.

What do we need?

Organization of the project

It is necessary for us to create a /jni folder and to copy the contents of the project /jni folder, that was downloaded from svn (or simply to copy complete folder /jni), in the Android project. After that we need to add the following files from the downloaded project:

  • SerialPort.java

  • Application.java

  • SerialPortActivity.java

  • SerialPortFinder.java

The given files allow us to work with the COM port but you will need to edit the files to serve the needs of the project. It is known all devices in the systems are similar to a *nix one are on a path /dev. To establish a path to the device (COM port) and baud rate it is necessary to set the appropriate values of the fields in the Application.java file:

String path = -path to device-;
int baudrate = -baud rate-;

Class SerialPortActivity.java is an extension of Activity class and contains an abstract method protected abstract void onDataReceived (final byte [] buffer, final int size). You can inherit the Activity from this class where they will work with the serial port, and to process data acquisition from the port having redefined the method onDataReceived.

@Override
protected void onDataReceived(final byte[] buffer, final int size) {
runOnUiThread(new Runnable() {
public void run() {
//TO DO your logic
}
});
}
It is possible to extract logic of the information system port in your own class/classes and not to use the inheritance from SerialPortActivity.java. You can receive the lists of all the devices and their paths by means of class SerialPortFinder.java with its methods getAllDevices () and getAllDevicesPath () accordingly. The write-In port is carried out by using a simple record in OutputStream created by means of class SerialPort.java, COM port.
mOutputStream.write(new String(“text”).getBytes());
mOutputStream.write('\n');

Accessing a serial port

Native code loading in the Android application may be found in class SerialPort.java by calling System.loadLibrary (‘ serial_port ‘):

private native static FileDescriptor open(String path, int baudrate, int flags);
public native void close();
static {
System.loadLibrary("serial_port");
}

The parameter serial_port is a module that has occurred as a result of code C compilation through/via NDK. It is specified in file make /jni/Android.mk. File SerialPort.c in /jni folder and contains native functions of the system calls to work with Serial port. Such parameters for the COM port as Data bits, Parity, Stop bits and the others may be changed in this file by means of structure termios, for example:

  cfg.c_cflag |= ~PARENB;
cfg.c_cflag &= ~CSTOPB;
cfg.c_cflag &= ~CSIZE;
cfg.c_cflag |= CS8;
(Data bits=8, Parity=none, Stop bits=1)

This information about termios.h may be found under the following links: http://ulisse.elettra.trieste.it/services/doc/serial/config.html http://pubs.opengroup.org/onlinepubs/007908775/xsh/termios.h.html

After changing the file SerialPort.c it is necessary to compile the libraries as follows:

  • Open command line

  • Go to the NDK folder

  • Set path to the Android project – set NDK_PROJECT_PATH= -path to your android project-

  • Run – ndk-build

The libraries will be compiled and added in a /libs folder of your project. After that it is possible to perform the following command in order to install an Android application in a device:

adb install <path to your .apk file>

Result

As a result we have all the instruments that can help us to connect a third-party device via a serial port. Sending and receiving data using these instruments also allow us to manage devices which give us great opportunities for new business ideas.

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