How to Simplify Device Debugging with a USB HID Logger

A USB HID (Human Interface Device) logger captures data sent between a USB device (like a keyboard) and a host computer. Because HID devices do not require custom drivers, they are highly compatible across Windows, macOS, and Linux.

Here is a step-by-step implementation guide using a microcontroller like the Raspberry Pi Pico or an Arduino Micro (ATmega32U4). 🛠️ Hardware Requirements

Microcontroller: Raspberry Pi Pico, Adafruit ItsyBitsy M4, or Arduino Micro.

Storage Module: MicroSD card breakout board (SPI interface).

Connectors: USB Host Shield or a dual-USB development board (if sniffing physical hardware). Wiring: Jumper wires and a breadboard. 🏗️ Step 1: Environment Setup

Download and install the Arduino IDE or VS Code with PlatformIO. Install the necessary USB libraries.

For Arduino/ATmega32U4: Use the built-in HID.h and Keyboard.h. For Raspberry Pi Pico: Install the TinyUSB stack library.

Install the standard SD.h and SPI.h libraries for data storage. 🔌 Step 2: Wiring the Storage

Connect your MicroSD card module to the microcontroller using the SPI protocol. Here is a standard pin mapping example for Arduino: VCC ➡️ 5V / 3.3V GND ➡️ GND MISO ➡️ Digital Pin 12 MOSI ➡️ Digital Pin 11 SCK ➡️ Digital Pin 13 CS (Chip Select) ➡️ Digital Pin 4 💻 Step 3: Writing the Firmware Core

The firmware must initialize the USB stack, detect data payloads, translate keycodes, and save them to the SD card.

#include #include #include #include // Example using Mbed/TinyUSB framework const int chipSelect = 4; File logFile; void setup() { // Initialize SD Card if (!SD.begin(chipSelect)) { while (1); // Halt if SD card fails } // Create or open the log file logFile = SD.open(“usb_log.txt”, FILE_WRITE); if (logFile) { logFile.println(“— Logger Started —”); logFile.close(); } } void loop() { // Check for incoming HID report data // Translate HID Usage IDs (e.g., 0x04 = ‘A’) into ASCII characters uint8_t keycode = get_incoming_hid_report(); if (keycode != 0) { char printable_char = translate_hid_to_ascii(keycode); // Log data to SD card logFile = SD.open(“usb_log.txt”, FILE_WRITE); if (logFile) { logFile.print(printable_char); logFile.close(); // Flush data immediately to prevent data loss } } } Use code with caution. 🔄 Step 4: Mapping HID Codes to ASCII

USB HID devices do not transmit standard ASCII characters; they send HID Usage IDs. Your code must include a lookup table or a switch-case statement to translate these bytes. HID code 0x04 translates to A HID code 0x1E translates to 1

You must also monitor the Modifier Byte to detect if the Shift or Ctrl keys are being held down to log uppercase letters or symbols accurately. 🔍 Step 5: Testing and Debugging Connect the microcontroller to your PC via its USB port. Open a text editor on your computer.

Use the Arduino Serial Monitor to print the raw HID reports to verify data capture.

Unplug the device, remove the SD card, and check usb_log.txt on a computer to ensure formatting is correct. ⚠️ Security and Ethics Note

USB HID loggers (specifically keyloggers) can capture sensitive information like passwords and personal data. Ensure you only build, deploy, and test this device on hardware and networks that you own or have explicit, documented permission to audit. If you want to tailor this project, let me know: What specific microcontroller hardware do you plan to use?