树莓派+Python读取USB HID模式RFID设备解码问题求助

Hey Federico, let's break down how to decode that HID RFID data and get your tag code properly!

First off, most HID-mode RFID readers act like USB keyboards—they don't send raw tag data directly; they send keyboard scan codes (the same signals your keyboard sends when you press a key). That's why you're seeing those random numbers instead of your 210054232F tag code.

Let's fix this step by step: #

1. Map those scan codes to actual characters

You already noticed the output pairs like 1 31 1—this is likely the reader's way of sending a single key press. The middle number is the USB HID scan code, and the surrounding 1s are just framing bytes. Here's a quick mapping for the characters in your tag:

Looking at your output, you can already match some entries to your tag:

• 1 31 1 → 1
• 1 30 1 → 0
• 1 32 1 → 2

2. Adjust your script to read the right chunk size

Your current code reads 16 bytes at once, which mixes multiple key press reports together. Try reading 3 bytes at a time (since each key press seems to be wrapped in 3 bytes):

import sys

# Open the HID device
with open('/dev/hidraw0', 'rb') as fp:
    # Mapping scan codes to your tag's characters (expand this as needed)
    scan_code_map = {
        30: '0',
        31: '1',
        32: '2',
        33: '3',
        34: '4',
        35: '5',
        39: '/',
        44: 'F'
    }
    
    while True:
        # Read 3 bytes per key press report
        buffer = fp.read(3)
        if len(buffer) != 3:
            continue
            
        prefix, scan_code, suffix = ord(buffer[0]), ord(buffer[1]), ord(buffer[2])
        
        # Only process valid key presses (ignore empty/reset signals)
        if prefix == 1 and suffix == 1 and scan_code != 0:
            char = scan_code_map.get(scan_code, f"[UNKNOWN:{scan_code}]")
            print(char, end='')  # Print without newlines to build the full tag code

3. Get the official HID report structure (if the above doesn't work)

If the 3-byte assumption is wrong, you can find the exact report format of your device using the hidraw-dump tool:

sudo hidraw-dump /dev/hidraw0

This will output the device's HID report descriptor, which tells you how many bytes per report, what each byte represents (e.g., modifier keys, scan codes), and more.

4. Use a dedicated HID library for easier handling

Manual byte parsing can get messy. Try the hidapi Python library, which handles HID device communication and report parsing out of the box:

1. Install it first:

   pip install hidapi
   

2. Find your device's Vendor ID (VID) and Product ID (PID) with lsusb (look for your RFID reader entry, e.g., ID 1234:5678 where 1234 is VID and 5678 is PID)
3. Use this script:

   import hid
   
   # Replace with your device's VID/PID from lsusb
   VENDOR_ID = 0x1234
   PRODUCT_ID = 0x5678
   
   device = hid.device()
   device.open(VENDOR_ID, PRODUCT_ID)
   
   try:
       scan_code_map = {30:'0',31:'1',32:'2',33:'3',34:'4',35:'5',39:'/',44:'F'}
       while True:
           # Read input reports (adjust the 64 to match your device's report size)
           report = device.read(64)
           if not report:
               continue
           
           # Extract the scan code (adjust the index based on your report descriptor)
           scan_code = report[1]
           if scan_code != 0:
               print(scan_code_map.get(scan_code, f"[?{scan_code}]"), end='')
   finally:
       device.close()
   

Final Notes #

Since your reader outputs 210054232F directly in the terminal, it's definitely emulating a keyboard. Once you map the scan codes correctly, you'll see the full tag code printed out as a single string.

内容的提问来源于stack exchange，提问作者Federico Pinciaroli