Communication with serial port "/dev/ttyS3" in Unity

I'm trying to establish communication with my NFC reader, which is built into my tablet and trying to do it in Unity. The port of NFC in tablet is /dev/ttyS3. I can't use the using System.IO.Ports; library because Android doesn't support it.

Does anyone know a way to guide me toward a solution? Or has anyone dealt with this before?

So simply, I've given up on unity. You could make an aar library, import it into unity and reference it there.

In the end, I stayed in android studio and focused on the port I needed and referenced and started listening.

I found that the tablet uses a "GM 02 card reading module" which communicates via "ttyS3" and baud rate "115200".

Maybe that will help someone.

import android.os.Bundle
import android.util.Log
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity
import java.io.File
import java.io.FileInputStream
import java.io.IOException

class MainActivity : AppCompatActivity() {

    private val serialPortPath = "/dev/ttyS3"
    private lateinit var inputStream: FileInputStream
    private lateinit var textViewData: TextView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Inicializace TextView
        textViewData = findViewById(R.id.textViewData)
        textViewData.text = "Waiting for data..."

        // Setting the serial port after initializing the UI components
        setupSerialPort()
    }

    private fun setupSerialPort() {
        val file = File(serialPortPath)

        if (!file.exists()) {
            updateTextView("Serial port $serialPortPath does not exist")
            return
        }

        if (!file.canRead() || !file.canWrite()) {
            updateTextView("No read/write access to $serialPortPath")
            return
        }

        try {
            inputStream = FileInputStream(file)

            Thread {
                val buffer = ByteArray(64)
                while (true) {
                    try {
                        val bytesRead = inputStream.read(buffer)
                        if (bytesRead > 0) {
                            // Přijatá data
                            val hexData = buffer.copyOf(bytesRead).joinToString(" ") {
                                String.format("%02X", it)
                            }
                            Log.d("SerialPort", "Received raw data: $hexData")

                            // Verification of the beginning and end of the frame
                            if (buffer[0] == 0x02.toByte() && buffer[bytesRead - 1] == 0x03.toByte()) {
                                val cardType = buffer[2]
                                val cardData = buffer.copyOfRange(3, bytesRead - 2).joinToString("") {
                                    String.format("%02X", it)
                                }

                                updateTextView("Card Type: $cardType, Card Data: $cardData")
                            } else {
                                // Neúplný rámec
                                updateTextView("Incomplete or invalid frame: $hexData")
                            }
                        }
                    } catch (e: IOException) {
                        updateTextView("Error reading from serial port: ${e.message}")
                        break
                    }
                }
            }.start()

        } catch (e: Exception) {
            updateTextView("Error initializing serial port: ${e.message}")
        }
    }




    private fun updateTextView(text: String) {
        if (::textViewData.isInitialized) {
            runOnUiThread {
                textViewData.text = text
            }
        } else {
            Log.e("SerialPort", "TextView is not initialized yet!")
        }
    }

    override fun onDestroy() {
        super.onDestroy()
        try {
            inputStream.close()
        } catch (e: IOException) {
            Log.e("SerialPort", "Error closing serial port", e)
        }
    }
}

AndroidManifest permission

<uses-permission android:name="android.permission.WRITE_SETTINGS" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>