Electronic – arduino – RFID Reader UART

Have you tried using a powered USB hub?

What is being stored into the code[] array is a series of binary values:

code[bytes_read] = val;

The actual values retrieved by val = mySerial.read(); are most likely values from 0x00 through 0xff (0 to 255 in decimal).

1. You need to decide how you want those byte values displayed: As hexadecimal digit pairs(00 .. ff), as decimal numbers (0 .. 255) or as the ASCII representations of those values (which is what is happening now).

   • Note that byte values up to 31 have no standard visual representation (hence the junk characters), 32 is a space, 33 onward are symbols, numbers, letters and so on up to value 127.
   • 128 through 255 again have different representations on different systems, "Extended ASCII"

2. Apart from this, a C string consists of a series of ASCII characters terminated by a null, or 0 value. Without appropriately terminating a string, print() and println() will not meaningfully terminate the displayed string.

In short, you will have to adopt one of the several ways of displaying byte values in readable form. A bit of searching on the web or on StackOverflow should show you several algorithms to achieve this in C.

Only then would you see what you are expecting to see in the serial monitor.