Error when opening Serial Monitor: "We can't find the device"

ptillisch · December 12, 2024, 2:13am

Thanks for reporting this @marvin_serpas and @wassupgcode_24. I performed an investigation and found that I could reproduce it under the following conditions:

The board has the WCH CH340 USB chip.
The operating system is Windows.
The latest version (3.9.2024.9) of the CH340 driver is installed.

I have reported the problem to the Arduino Cloud developers:

github.com/arduino/arduino-create-agent

`open` command fails to connect to boards with CH340 USB chip on Windows

opened 03:26PM - 12 Dec 24 UTC

per1234

topic: code os: windows type: imperfection

### Describe the problem The WCH CH340 USB to serial bridge chip is common on b…oards used by the Arduino community. The manufacturer of this chip recently released a new version of the Windows driver, which users are receiving via a Windows update. 🐛 The port is spuriously closed immediately after an `open` command under the following conditions: - The port is produced by a CH340 USB chip. - The user is using the Windows operating system - The user has the latest CH340 driver version (3.9.2024.9) installed. ### To reproduce #### Equipment - Any device that has a WCH CH340 USB chip. - A Windows machine. #### Steps 1. Connect the device to your computer with a USB cable. 1. Open Windows **Device Manager**. 1. Find the device under the "**Ports (COM & LPT)**" section of the **Device Manager** tree. 1. Right click on the device. A context menu will open. 1. Select "**Properties**" from the menu. The "**USB-SERIAL CH340 (COM_n_) Properties**" dialog will open. 1. Select the "**Driver**" tab in the dialog. 1. Verify that version `3.9.2024.9` is shown in the "**Driver Version**" field of the dialog. 1. Close the dialog and the **Device Manager** window. 1. Start **Arduino Cloud Agent**. An icon will appear in the Windows "[notification area](https://support.microsoft.com/en-us/windows/customize-the-taskbar-notification-area-e159e8d2-9ac5-b2bd-61c5-bb63c1d437c3)". 1. Click the **Arduino Cloud Agent** icon in the notification area. A menu will open. 1. Select "**Open Debug Console**" from the menu. The "**Arduino Cloud Agent Debug Console**" page will open in your browser. 1. Type `open <port name> 9600` in the field at the bottom of the page. (where `<port name>` is the name of the serial port produced by the CH340 device) 🐛 The port is opened, but then immediately closed: ```text open COM17 9600 { "Cmd": "Open", "Desc": "Got register/open on port.", "Port": "COM17", "Baud": 9600, "BufferType": "default" } { "Cmd": "Close", "Desc": "Got unregister/close on port.", "Port": "COM17", "Baud": 9600 } Shutting down writer on COM17 writerBuffered just got closed. make sure you make a new one. port:COM17 ``` ### Expected behavior Port remains open until disconnected or a `close` command is executed. ### Cloud Agent version d36d0e142b8b46c0cde117f94b37b37422b806d7 ### Operating system - Windows ### Operating system version - Windows 11 ### Additional context I found that the disconnection is caused by this code: https://github.com/arduino/arduino-create-agent/blob/d36d0e142b8b46c0cde117f94b37b37422b806d7/serialport.go#L158-L165 Here is a derived minimal Go program that can be used to reproduce the fault: ```go package main import ( "log" "time" "go.bug.st/serial" ) const portName string = "COM17" func main() { mode := &serial.Mode{ BaudRate: 9600, } port, err := serial.Open(portName, mode) if err != nil { log.Fatal(err) } timeCheckOpen := time.Now() buff := make([]byte, 100) for { n, err := port.Read(buff) if err != nil { log.Fatal(err) break } if n <= 0 { diff := time.Since(timeCheckOpen) if diff.Nanoseconds() < 1000000 { log.Println("Too soon since last empty read") break } timeCheckOpen = time.Now() } } } ``` --- This problem causes the [Arduino Cloud Editor **Serial Monitor**](https://docs.arduino.cc/arduino-cloud/guides/editor/#serial-monitor) to fail to connect to the port, with the following error notification: > **We can’t find the device, please make sure it is connected via serial port. You can still see log history here, but data won’t be printed until new connection.** --- The fault does not occur after I install the older versions 3.8.2023.2 and 3.7.2022.1 of the CH340 driver. --- The fault does not occur when using [`arduino-cli monitor`](https://arduino.github.io/arduino-cli/dev/commands/arduino-cli_monitor/). --- The fault does not occur on my macOS and Linux machines. --- The fault does not occur when using boards with other USB chips (FTDI FT232R, Silicon Labs CP2104, ATmega16U2 w/ [Arduino firmware](https://github.com/arduino/ArduinoCore-avr/tree/master/firmwares/atmegaxxu2)). --- Originally reported at https://forum.arduino.cc/t/error-when-opening-serial-monitor-we-cant-find-the-device/1331419/1 #### Additional reports: - https://forum.arduino.cc/t/error-when-opening-serial-monitor-we-cant-find-the-device/1331419/3 ### Issue checklist - [X] I searched for previous reports in [the issue tracker](https://github.com/arduino/arduino-create-agent/issues?q=) - [X] I verified the problem still occurs when using the latest version - [X] My report contains all necessary details

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Please only comment on the GitHub issue thread if you have new technical information that will assist with the resolution. General discussion and support requests are always welcome here on the Arduino Forum.

Until the bug is resolved, I can suggest the workaround of rolling back to a previous version of the CH340 driver. I found that Serial Monitor works perfectly when I am using that version of the driver.

Close the Serial Monitor window if it is still open.
Click the following link to download the previous version of the driver from the chip manufacturer's website:
https://www.wch-ic.com/downloads/file/65.html?time=2023-03-16%2022:57:59
Wait for the download to finish.
Run the downloaded CH341SER.EXE file.
A "User Account Control" dialog may now appear asking "Do you want to allow this app to make changes to your device?". Click the "Yes" button.
A "DriverSetup(X64)" dialog will open. Click the "INSTALL" button in the dialog.
Wait for the driver installation to finish, as indicated by the appearance of a "Driver install success!" dialog.
Click the "OK" button in the "Driver install success!" dialog.
The dialog will close.
Click the X icon at the top right of the "DriverSetup(X64)" dialog
The dialog will close.
Close Arduino IDE if it is running.
Connect the Arduino board to your computer with a USB cable.
Open the Windows Device Manager.
Select View > Devices by type from the Device Manager menus.
Open the "View" menu.
If there is a ✓ to the left of the "Show hidden devices" menu item, click on "Show hidden devices" to disable it.
Open the "Ports (COM & LPT)" section of the Device Manager tree.
You should see a port identified as "USB-SERIAL CH340 (COMn)" under the "Ports (COM & LPT)" section (where "COMn" is some serial port e.g., COM4). Double click on that item.
The "USB-SERIAL CH340 (COMn) Properties" dialog will open.
Select the "Driver" tab of the "USB-SERIAL CH340 (COMn) Properties" dialog.
You will see a "Roll Back Driver" button in the dialog. If it is not clickable, perform the following instructions:
1. Click the "Update driver" button.
  An "Update Drivers Device - USB-SERIAL CH340 (COMn)" dialog will open.
2. Click on "Search automatically for drivers" in the "Update Drivers Device - USB-SERIAL CH340 (COMn)" dialog.
3. You should now see the driver installation wizard update the driver. Wait for the update to finish, as indicated by the message "Windows has successfully updated your drivers" in the dialog.
  It is possible you will instead see the message "The best drivers are already installed". If so, please stop following the instructions here and reply on the forum thread to let me know. I'll provide alternative instructions you can follow.
4. Click the "Close" button in the "Update Drivers Device - USB-SERIAL CH340 (COMn)" dialog.
  The dialog will close.
Click the "Roll Back Driver" button in the "USB-SERIAL CH340 (COMn) Properties" dialog.
The "Driver Package rollback" dialog will open.
Click the radio button next to "My apps don't work with this driver" in the "Driver Package rollback" dialog .
Click the "Yes" button.
The "Driver Package rollback" dialog will close.
Click the "Close" button in the "USB-SERIAL CH340 (COMn) Properties" dialog.
Close the Device Manager window.

Now try opening Serial Monitor again, just as you did before. Hopefully this time it will work as expected.

Please let me know if you have any questions or problems while following those instructions.

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Error when opening Serial Monitor: "We can't find the device"

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