Выписываю благодарность автору замечательной библиотеки usb_serial_for_android. К сожалению quick start, который он предлагает не содержит примера для записи в порт. Исправим это.

Приведен код активити приложения с тремя кнопками.

package com.example.dimon.usbserialtest;

import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;

import android.graphics.Color;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.hardware.usb.UsbManager;
import android.hardware.usb.UsbDeviceConnection;
import java.util.List;
import java.io.IOException;

import com.hoho.android.usbserial.driver.UsbSerialPort;
import com.hoho.android.usbserial.driver.UsbSerialProber;
import com.hoho.android.usbserial.driver.UsbSerialDriver;

public class MainActivity extends ActionBarActivity {

private static UsbSerialPort sPort = null;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}

//write the serial data

private void writetoserial(int col) {
    byte[] colorBytes = {(byte)Color.red(col),
            (byte)Color.green(col),
            (byte)Color.blue(col),
            0x0A};
    //remove spurious line endings so the serial device doesn't get confused
    for (int i=0; i<colorBytes.length-1; i++){
        if (colorBytes[i] == 0x0A){
            colorBytes[i] = 0x0B;
        }
    }

    // Find all available drivers from attached devices.
    UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);
   List availableDrivers = UsbSerialProber.getDefaultProber().findAllDrivers(manager);
    if (availableDrivers.isEmpty()) {
        return;
    }

    // Open a connection to the first available driver.
    UsbSerialDriver driver = availableDrivers.get(0);
    UsbDeviceConnection connection = manager.openDevice(driver.getDevice());

    if (connection == null) {
        return;
    }

    try {
        sPort = driver.getPorts().get(0);
        sPort.open(connection);
        sPort.setParameters(115200, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE);

        sPort.write(colorBytes, 500);
    } catch (IOException e) {
        // Deal with error.
        try {
            sPort.close();
        } catch (IOException e2) {
            // Ignore.
        }
        sPort = null;
        return;
    }
}

public void onClickRed(View view){
    //write the serial data
    int col;
    col = 1;
    writetoserial(col);
}

public void onClickBlue(View view){
    //write the serial data
    int col;
    col = 2;
    writetoserial(col);
}

public void onClickGreen(View view){
    //write the serial data
    int col;
    col = 3;
    writetoserial(col);
}


}