Im using Arduino Uno with RFID Reader and SD card components. I'm trying to send my SD card text file contents to a laptop via serial port. The laptop will receive my data as ASCII characters
I have a text file with data made out of "0,1,2..9, A, B, C...F" characters. This text file contains RFID IDs in Hexadecimal form
4F5C23AA
5AFF0123
566777CC
and I want to write my text file content as hexadecimal numbers to the serial port
Serial.write(0x0Z) // Z in here should be every data in text file
// For example :
Serial.write(0x04);
Serial.write(0x0F);
Serial.write(0x05);
// I want to write all text file content
Please explain exactly what you want to do. It would be best to explain why, because "something like this" suggests that you don't yet quite understand the goal.
The device on the other hand is a laptop. My Arduino Uno and Laptop communicate through a port. So the laptop takes the ASCII equivalent of what I send. It will convert it via c# function and write it to the web app.
you need to parse the text file to read the bytes and then write the bytes out.
if the RFID is only 4 bytes long, you could use strtoul()
const char * rfids[] = {"4F5C23AA", "5AFF0123", "566777CC"};
const byte count = sizeof rfids / sizeof * rfids;
void setup() {
Serial.begin(115200);
Serial.println("------------------");
// or traditional for loop
for (byte i = 0; i < count; i++) {
unsigned long r = strtoul (rfids[i], nullptr, 16);
Serial.print("I read 0x"); Serial.println(r, HEX);
}
Serial.println("------------------");
// or if you want to use the fancy range based for loop
for (auto &&id : rfids) {
unsigned long r = strtoul (id, nullptr, 16);
Serial.print("I read 0x"); Serial.println(r, HEX);
}
}
void loop() {}
now the actual bytes are in memory (little endian format) so you can send them out if you want to.
sscanf() or fscanf() would also be able to parse an hex number from a string (or file for fscanf)
EDIT: now you modified your first post so my answer and work does not make any sense. Good luck.
so you have ASCII in the text file and you want to dump it to Serial? just read the bytes (they will be ascii) and write them out ... nothing special is required
PS: now that you modified your first post so my previous answer and work does not make any sense. so Good luck.
I have arduino uno with RFID-RC522 reader and SD card components. I'm reading a text file from my SD card. This text file contains card IDs in hexadecimal form and it only consists characters of " 0,1,2,...,8,9,A,B,C...F ". My text file looks like this
4CFB33DA
998877AA
7DCAB1A9
8D6F0503
AFD234FA
On the other end of the arduino there is a laptop. Arduino chip and laptop communicates through a serial port. Arduino send these text file's contents with the code below
myFile = SD.open("myFile.txt"); // pretty basic file reading
if (myFile) {
while (myFile.available()) {
Serial.write(myFile.read()); // basic serial write
// Serial.write("0x0"+myFile.read()) // I tried this but it sends nonsense
}
myFile.close();
You want to convert each binary 8 bit byte of data to a pair of 7-bit ASCII characters.
Ok, so you have to isolate each nibble (4 bits) of the byte and then convert each nibble to the corresponding ASCII char for transmission.
String hex2A(int valu)
{
int msn = ( valu & 0b11110000 ); // isolate MSN
msn >> 4; // shift right
int lsn = ( valu & 0b00001111 ); // No shift needed on bottom nibble
if (msn > 9) msn = msn +7; // bump A-F into that part of ASCII
msn = msn + int("0"); // Add ASCII offset
//
if (lsn > 9) lsn = lsn +7; // Ditto for LSN
lsn = lsn + int("0");
//
return (String(msn, 0) + String(lsn, 0) );
}
That should work.
If you call it with one byte it should return a two character string ready to print to the serial port.
Hi @AmogusFloppa. I appreciate you making the effort to reference the previous topic when you created a new one on the subject. However, I still feel that there is no need to have two separate topics on the identical subject, and that having two risks confusion and wasted time caused by parallel discussions. For that reason I have merged the two topics into one.
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