I am trying to transmit serial data from terminal to Arduino and I want to reconfirm that its the same data. But I am not able to get the right answer. I want data to be HEX. I want to check only the third last and last bytes since they will be changing every time.

I tried to write it in 2 different ways but none worked.

First try:

byte thisByte[]={0xAA, 0xBB, 0x06, 0x00, 0x00, 0x00, 0x01, 0x01, 0x03, 0x03};
void setup()
  // start serial port at 9600 bps:

void loop()
  while (Serial.available())
    // get the new byte:
    byte thisByte = Serial.read();
    // add it to the inputString:
    //inputString += char(intChar);

    if(thisByte == 0x03 || thisByte == 0x03)
      Serial.print(thisByte, 'Hello');
      //digitalWrite(13, HIGH);   // turn the LED on (HIGH is the voltage level)
      delay(50);             // wait for a second
      Serial.print(thisByte, 'Nothing');
      //digitalWrite(13, LOW);    // turn the LED off by making the voltage LOW
    Serial.print(" | ");

Second try:

const byte message[]={0xAA, 0xBB, 0x06, 0x00, 0x00, 0x00, 0x01, 0x01, 0x03, 0x03};
boolean found = false;

byte byte1 = 0xAA;
byte byte2 = 0xBB;
byte byte3 = 0x06;
byte byte4 = 0x00;
byte byte5 = 0x00;
byte byte6 = 0x00;
byte byte7 = 0x01;
byte byte8 = 0x01;
byte byte9 = 0x03;
byte byte10 = 0x03;

const byte Hallo;
//void rules();
void setup() {
  // put your setup code here, to run once:

void loop() {
  // put your main code here, to run repeatedly:
  // put your main code here, to run repeatedly:
  //int hexIn = Serial.read();
    delay(10);  //small delay to allow input buffer to fill
    byte c = Serial.read();
    byte message = c;

    //Serial.print(" | ");

    //if (c =!byte 0xAA && c =!byte 1 0xAA && c =!byte 0xAA && c =!byte 0xAA && c =!byte 0xAA && c =!byte 0xAA && c =!byte 0xAA && c =!byte 0xAA);

    if (c == message);
    //Serial.print("I received: ");

    // byte c = Serial.read();  //gets one byte from serial buffer
    // readmessage += c;
  } //makes the string readString
  //readString=""; //clears variable for new input
  • 1
    What, exactly, is being entered into the serial console? Are you typing literal "0x03" or similar? Or are you somehow typing the 8-bit value 0x03? Dec 6 '17 at 17:08
  • I want data to be HEX ... i do not think that you understand what hex really means
    – jsotola
    Dec 6 '17 at 20:41
  • what does right answer mean? ... so far only you know what you expect to see ... we need to know also, before we can help you.
    – jsotola
    Dec 6 '17 at 21:05
  • Thank you for your reply. I was providing a data from terminal but not like 0x03. But AA BB 00 03 so. But now your code gave me a idea how it works. Thanks once again Dec 7 '17 at 15:51
  • Plus one more thing I wanted to ask you was that I am trying to send data packet completely and not single byte. So what I actually want to do or my work is to for eg: 0xAA, 0xBB, 0x06, 0x00, 0x00, 0x00, 0x01, 0x01, 0x03, 0x03 Dec 7 '17 at 15:53

First, you have to understand what “hex” means. Basically, you are representing binary data as text, where each byte is represented as two characters. For example, the number 42 is represented as either “2A” or “2a”. In C and C++, you can write this number as 0x2a, but I assume your serial stream sends the raw hex data, without the “0x” prefix. Thus, on the serial stream you may receive the character “2” (character code 0x32 = 50 in decimal) followed, some time later, by “a” (charcode 0x61 = 97).

What you need is a conversion routine that takes these characters and reconstructs the binary data out of them. Here is one such routine I use. You have to provide it with an input string in and an output array out large enough to store the resulting binary data. The function will return the number of bytes filled in *size:

 * Convert an hex string to binary. Spaces are allowed between bytes.
 * The output array is supposed to be large enough.
 * On return, *size is the size of the byte array.
static void hex2bin(uint8_t *out, const char *in, size_t *size)
    size_t sz = 0;
    while (*in) {
        while (*in == ' ') in++;  // skip spaces
        if (!*in) break;
        uint8_t c = *in>='a' ? *in-'a'+10 : *in>='A' ? *in-'A'+10 : *in-'0';
        c <<= 4;
        if (!*in) break;
        c |= *in>='a' ? *in-'a'+10 : *in>='A' ? *in-'A'+10 : *in-'0';
        *out++ = c;
    *size = sz;

As a mere convenience, the function above accepts spaces within the string, but only between bytes. Notice however that it does not attempt to do any error checking. You may want to improve it in this respect.

Next, you have to devise a way to frame your messages on the serial line. Serial does not provide any framing per se: it only transmits byte one by one. When dealing with text, a common scheme is to send a carriage return (\r) to indicate the end of a message. With this convention, you sketch has to buffer the bytes it receives until it sees a carriage return. Then it can process the whole message as a whole. This approach is nicely explained in the blog post Reading Serial on the Arduino, by Majenko, a regular contributor to this site.

Here is an example that reads an hex string, converts it to binary, and then sends it back as hex again:

void setup()

void loop()
    static char buffer[1024];
    static size_t length = 0;

    if (Serial.available()) {
        char c = Serial.read();

        // On carriage return, process the received data.
        if (c == '\r') {
            Serial.println();  // echo

            // Properly terminate the string.
            buffer[length] = '\0';

            // Convert the hex data to a byte array.
            size_t byte_count = length/2;
            uint8_t data[byte_count];
            hex2bin(data, buffer, &byte_count);

            // Echo back the byte array in hex.
            for (size_t i = 0; i < byte_count; i++) {
                Serial.print(data[i], HEX);
                Serial.print(" ");

            // Reset the buffer for next line.
            length = 0;

        // Otherwise buffer the incoming byte.
        else if (length < sizeof buffer - 1) {
            Serial.write(c);  // echo
            buffer[length++] = c;

Notice the lines with the comment “echo”: they are meant to help you see in the terminal what you are typing. You can remove them if you do not what the Arduino to echo your typing. I tested it by sending

AA bb06 000000 0101 03 03

and it replied

AA BB 6 0 0 0 1 1 3 3 
  • Thank you very much for your reply. It worked really good. I mwill try more to code on this topic in order to understand it completely. Dec 7 '17 at 15:48

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