A USB module for [Arduino](https://www.ampheo.com/c/development-board-arduino) is basically the hardware and firmware that lets an Arduino board talk to a computer (or sometimes directly to other USB devices). Here’s what it’s used for:

**1. Programming / Bootloading**

* On most Arduino boards (Uno, Nano, Mega), the USB interface is handled by a small USB-to-serial chip (e.g., [ATmega16U2](https://www.ampheo.com/search/ATmega16U2), [CH340](https://www.ampheo.com/product/ch340t-27265631), FT232).
* When you connect the board to your PC via USB, this module converts USB data into UART signals that the main [microcontroller](https://www.ampheo.com/c/microcontrollers) (e.g., [ATmega328P](https://www.ampheo.com/search/ATmega328P)) understands.
* That’s how you can upload sketches from the Arduino IDE.

**2. Serial Communication with PC**

* Once programmed, the same USB link acts as a virtual COM port.
* You can use the Serial Monitor or external software (like Python scripts, MATLAB, Processing) to send/receive data.
* Useful for debugging, data logging, or controlling Arduino from the PC.

3. USB Device Emulation (if supported)

* Some boards (e.g., [Arduino Leonardo](https://www.ampheo.com/product/a000052-25542581), Micro, Due, or boards with [ATmega32U4](https://www.ampheo.com/search/ATmega32U4) or [SAMD21](https://www.ampheo.com/search/SAMD21)) have built-in USB peripherals.
* These can emulate a USB Keyboard, Mouse, [Joystick](https://www.onzuu.com/category/joystick), MIDI controller, or generic HID device directly, without a separate module.
* Example: turning Arduino into a custom gamepad.

4. Host Mode (with USB Host Shield or OTG boards)

* Standard Arduinos can only act as USB devices.
* If you add a USB Host Shield (based on MAX3421E), the Arduino can talk to USB devices like:

* [Keyboards](https://www.onzuu.com/category/keyboards), mice
* Game controllers
* Smartphones (with OTG)
* Storage (with extra libraries)

* This expands Arduino projects into USB host applications (e.g., build a robot controlled by a USB joystick).

**5. Power Supply**

* The USB module also supplies 5V power to the Arduino when plugged into a computer.
* Some boards can be powered solely over USB (no external adapter needed).

**What to Do If It Doesn't Work? (Driver Issues)**
If your computer doesn't recognize your Arduino (especially common with clones using the CH340 chip), the problem is almost always a missing driver.
* Symptom: "USB device not recognized" or the COM port doesn't appear.
* Solution: You need to download and install the correct driver for the USB chip on your board. Search for "CH340 driver" or "[CP2102](https://www.onzuu.com/search/CP2102) driver" and install it.

**Summary:**
A USB module for [Arduino](https://www.ampheoelec.de/c/development-board-arduino) is mainly used to program the MCU, exchange data with the PC, power the board, emulate USB devices (on certain chips), or act as a USB host with add-on hardware.