FAQ
TL;DR: Compile succeeded (11% memory used), but upload failed with "A fatal error occurred: Could not open /dev/ttyS0". This points to a wrong or unstable serial port on Ubuntu. Use the guidance below to select the correct USB device and stabilize the connection. [Elektroda, CC_PL, post #20512534]
Why it matters: Linux Arduino IDE users can quickly fix ESP32 upload/serial issues without chasing drivers or reinstalling tools.
Quick Facts
- On Linux, USB serial devices appear as /dev/ttyUSBx (or /dev/ttyACMx); /dev/ttyS0 is not the USB connection. [Elektroda, khoam, post #20512593]
- The board enumerated as QinHeng CH340 (USB VID:PID 1a86:7523) via lsusb; select /dev/ttyUSB0 when present. [Elektroda, CC_PL, post #20512674]
- Match baud rates between Serial.begin() and Serial Monitor (e.g., 115200) to read output correctly. [Elektroda, khoam, post #20512681]
- After "Hard resetting via RTS pin...", some boards need manual RESET/BOOT to start printing. [Elektroda, CC_PL, post #20516508]
- A short, data USB cable and a different USB socket resolved intermittent disconnects for this ESP32. [Elektroda, CC_PL, post #20518044]
Why does Arduino IDE only show /dev/ttyS0 and fail to open it?
/dev/ttyS0 is a built‑in serial port, not the USB‑to‑UART used by ESP32. If the IDE lists only /dev/ttyS0, the board’s USB device did not enumerate as /dev/ttyUSBx. Check your USB cable and try another USB port. Once the USB interface comes up, select /dev/ttyUSB0 in Tools → Port. [Elektroda, khoam, post #20512593]
My ESP32 port appears as /dev/ttyUSB0 then disappears. How do I fix it fast?
Intermittent ports are often a cable issue. "Would suggest trying with a different USB cable to start with. Maybe even a shorter one." Use a data‑capable, short cable and avoid front‑panel ports. How‑To:
- Swap to a short, known‑good data USB cable.
- Try a different USB socket on the PC.
- Reopen Serial Monitor after reconnecting.
These steps usually stabilize /dev/ttyUSB0. [Elektroda, khoam, post #20512617]
Is this a USB power issue from my PC port?
Yes. Weak USB ports cause brownouts and disconnects during upload or when Wi‑Fi/BLE starts. Symptoms include a port that flaps and failed uploads. Try another USB socket or a powered hub. Keep Serial.begin() and the Serial Monitor baud in sync, but note that power problems can still break communication. [Elektroda, khoam, post #20512681]
After upload says "Hard resetting via RTS pin..." but nothing happens—what now?
That message means esptool toggled RTS/DTR to reset. Some boards don’t auto‑start afterward. Press RESET, or hold BOOT while pressing RESET if required by your board, then release. Open the Serial Monitor to view startup logs. If your board lacks proper autoreset wiring, manual RESET/BOOT is expected. [Elektroda, CC_PL, post #20516508]
Why doesn’t Arduino IDE react when I press RESET on the board?
The IDE doesn’t detect reset events; it only opens the serial port for logs. To see output after pressing RESET, keep the Serial Monitor open or reopen it immediately. This ensures you capture boot messages and confirms the board restarted correctly. [Elektroda, khoam, post #20516902]
Do baud rates need to match? What baud should I use on ESP32?
Yes. Set Serial.begin(115200) in your sketch and match 115200 in the Serial Monitor. Mismatched rates produce unreadable output. In this case, both code and monitor used 115200 and communication worked once the USB connection was stable. 115200 is a common default for ESP32 logging. [Elektroda, CC_PL, post #20512690]
Which USB-to-UART chip is on this board, and what should lsusb show?
This board uses a CH340 USB‑to‑serial converter. lsusb shows it as “QinHeng Electronics CH340” with VID:PID 1a86:7523. When present, the kernel creates a device like /dev/ttyUSB0. Select that port in Arduino IDE before uploading or opening the Serial Monitor. [Elektroda, CC_PL, post #20512674]
My ESP32-2432S035 doesn’t auto-reset like Espressif’s DevKit. Why?
Its reset wiring differs from the official Espressif DevKit. DTR/RTS autoreset may not be implemented the same. Use the board’s BOOT and RESET buttons when needed. As one expert noted, "This board has little to do with the official DevKit." [Elektroda, khoam, post #20516563]
How can I verify Linux permissions to access /dev/ttyUSB0?
Ensure your user belongs to the dialout group. Run: sudo usermod -a -G dialout $USER, then log out and back in. Without dialout membership, the IDE may not open the serial device. After re-login, verify the port appears and select it in Tools → Port. [Arduino, 2023]
Can charge-only USB cables cause 'no port' or upload failures?
Yes. Charge-only cables power the board but lack data lines, so no /dev/ttyUSBx device appears. Always use a data-capable USB cable. Swapping to a known-good data cable is a common and effective fix for missing or unstable serial ports. [Arduino, 2023]
What does 'crw-rw-rw- ... root dialout ... /dev/ttyS0' tell me?
That output shows a character device with read/write permissions and the dialout group owner. However, /dev/ttyS0 is a legacy serial port, not your ESP32’s USB interface. Focus on detecting and selecting /dev/ttyUSB0 for ESP32 communication. [Elektroda, CC_PL, post #20512534]
How much current can a USB 2.0 port supply, and does that affect ESP32 boards?
USB 2.0 ports supply up to 500 mA. ESP32 boards with Wi‑Fi/BLE can draw significant bursts. Marginal ports or long cables can cause voltage drops and disconnects. If the port flaps or uploads fail, use a rear motherboard port or a powered USB hub for stability. [USB – Wikipedia]
I'm giving shorter and shorter cables, but the port is not visible at the moment. 