要在Android設備上通過串口發送數據，可以使用Java中的SerialPort類來實現。以下是一個簡單的示例代碼，演示如何在Android設備上通過串口發送數據：

import android.hardware.usb.UsbDeviceConnection;
import android.hardware.usb.UsbManager;
import java.io.IOException;
import java.io.OutputStream;
import java.util.HashMap;

public class SerialPortSender {

    private UsbDeviceConnection connection;
    private OutputStream outputStream;

    public SerialPortSender(UsbDeviceConnection connection) {
        this.connection = connection;
        this.outputStream = connection.openOutputStream();
    }

    public void sendData(byte[] data) {
        try {
            outputStream.write(data);
            outputStream.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static UsbDeviceConnection findSerialPortConnection(UsbManager usbManager) {
        HashMap<String, UsbDevice> deviceList = usbManager.getDeviceList();
        UsbDeviceConnection connection = null;
        
        for (UsbDevice device : deviceList.values()) {
            if (device.getVendorId() == VENDOR_ID && device.getProductId() == PRODUCT_ID) {
                connection = usbManager.openDevice(device);
                break;
            }
        }
        
        return connection;
    }
}

在上面的代碼中，SerialPortSender類負責實現與串口的連接和數據發送功能。sendData方法用于發送數據，findSerialPortConnection方法用于查找串口連接。要使用該類，可以在Android應用的主活動中進行調用：

UsbManager usbManager = (UsbManager) getSystemService(Context.USB_SERVICE);
UsbDeviceConnection connection = SerialPortSender.findSerialPortConnection(usbManager);

if (connection != null) {
    SerialPortSender sender = new SerialPortSender(connection);
    byte[] data = "Hello, world!".getBytes();
    sender.sendData(data);
} else {
    Log.e(TAG, "Cannot find serial port connection");
}

在上面的代碼中，首先通過UsbManager獲取USB設備管理器實例，然后通過findSerialPortConnection方法查找串口連接。如果找到了串口連接，就可以實例化SerialPortSender類，并通過sendData方法發送數據。