This repository provides a diagnostic sketch to help identify serial communication failures, bootloader instability, or USB-related execution issues in Arduino Uno clones that use the CH340G or CH340C USB-to-serial chips. These issues often result in the board freezing, rebooting, or repeatedly executing a single line of code.
Ideal for diagnosing unstable boards with problematic USB-B ports, this tool uses a combination of LED patterns and timestamped serial output to visually and textually confirm whether your board is functioning normally.
Many users working with CH340G/CH340C-based Arduino Uno boards encounter problems where the program:
- Freezes a few seconds after upload
- Repeats the same output in the serial monitor
- Shows continuous LED blinking but no functional loop progression
This behavior is usually linked to hardware-level faults in the CH340 chip circuitry, especially how it handles power or serial line interference.
| # | Power Source | USB-B Connected | Serial Output Method | Result |
|---|---|---|---|---|
| 1 | USB-B (laptop) | Yes | USB-B | Program hangs and repeatedly prints the same line |
| 2 | USB-B (adapter) | Yes (power only) | None | Same issue — board freezes after a few seconds |
| 3 | Power jack | Yes | USB-B | Issue persists — same stuck behavior |
| 4 | Power jack | Planned test | USB-B (data only) | To test if removing USB power while keeping data solves issue |
- USB-B used for both power and serial (connected to a laptop): the board hangs and repeatedly outputs the same serial message.
- USB-B used only for power (connected to a wall adapter): same hanging behavior occurred.
- Board powered via the DC jack while USB-B was connected for serial: issue persisted.
- (Planned): Power via the DC jack and use USB-B only for data (disconnect 5V line) — to isolate whether the USB power line causes the fault.
Use the provided main.cpp sketch to test your board:
- Blinks the onboard LED at set intervals
- Prints each loop iteration with a millisecond timestamp
- Detects and warns if the loop is running too fast (indicating a reset or stuck loop)
If you observe the LED blinking in a fixed pattern while the same serial line is printed repeatedly — along with a "WARNING: Loop running too fast - possible reset/stuck?" message — your board is likely affected by the CH340-related issue.
To bypass the problematic CH340 chip, follow this workaround:
- Upload the program normally via the USB-B port.
- Disconnect the USB-B cable.
- Power the board through the power jack (recommended).
- Connect a USB-to-TTL adapter for serial output.
| TTL Adapter Pin | Arduino Uno Pin |
|---|---|
| GND | GND |
| TX | RX (Pin 0) |
| RX | TX (Pin 1) |
- Set the baud rate to
9600in the Serial Monitor (matches the sketch).
- Disconnect the USB-to-TTL adapter when uploading code — otherwise, your IDE may not connect to the board.
- Close the Serial Monitor before uploading a sketch — having it open can block the upload process and cause failures.
This tool is a lightweight and practical way to identify CH340-related board instability and serves as a quick validation for hardware troubleshooting.