RemoSwitch

Introduction

This project is designed to help with remote control/automatic testing. It equips with following features:

• Switching a TF card(microSD card) between two devices
• An onboard USB-TTL chip, which can be used to communicate with other devices
• An USB-A port with ability to control it's power

Typical Use Cases

If you want to remote/automatically control a development board, such as Raspberry Pi or any similar devices, you can use this device to switch the TF card between two devices, and control its power supply:

Quick Start

Firmware

If your device isn't pre-flashed with the firmware, you can use the following steps to flash it:

1. Download the firmware from the newest releases. The name should contains CH32v203G6U6 and end with .elf or .bin.
2. Get the wch-isp tool, which is used to flash the firmware.
3. Short the Boot0 pin on the device to enter the bootloader mode. Look to the bottom of the tf card slot, you can find two holes, connect them. Meanwhile, connect the device to your computer using a USB cable to power it on.
4. Flash it! wchisp flash firmware-CH32V203G6U6.bin
5. Check the device is working by connecting it to your computer. You shall see a USB device with VID:PID 0x1209:0x7410, which is the device.

Software

The host control program is written in Rust. There're pre-built binaries for Windows, Linux and MacOS available in the releases page. Note that the program is only tested against Linux. Please report it if you find and issues in the issues page.

Usage

Note: some commands may require root permission to function correctly.

First, you need to check whether the device is connected to your computer. You could use command remo -l to list available devices. With the device properly connected to the computer, you shall see its information like, this:

Found 1 devices:
Index   Device ID       Path
0       69F4A37B        /dev/hidraw6

Then, you can choose the device by using following methods:

• remo -i 0 to select the device with index 0
• remo -d 69F4A37B to select the device with ID 69F4A37B
• remo -p /dev/hidraw6 to select the device with path /dev/hidraw6

Change the index, ID or path to your own device.

After selecting the device, you can use the following commands to control the device.

Current Device Status

Using the option -s or --status to check the current device status. For example:

remo -i 0 -s

You shall see the current device status like this:

Status: 
        Mux: Open,
        Host: Connected,
        Dut: Disconnected,
        Board Power: On

Switch TF Card

Using the option -m or --mux to switch the TF card between two devices. To switch the TF card to device host(i.e. the device which is connected to the device via the USB-C port), you can use host as the argument; to switch the TF card to device client(i.e. the device which is connected to the device via the TF plug), you can use dut as the argument. For example:

remo -i 0 -m host
remo -d 69F4A37B -m dut

Besides, you can also use on or off as the argument to switch on or off the TF card switch. If off, all tf-data will be Hi-Z.

Power the on-board USB Port

Option -p or --pwr could be used to power the on-board USB Type-A port. Either on or off should be supplied as the argument. For example:

remo -i 0 -p on
remo -d 69F4A37B -p off

Details Usage

Make the PCB

Make sure you use a REAL GL3224, or you might having a lot of trouble in USB3.0 :( I spend a lot of time on this (sad

Here are some notice:

• Please: Electroless Nickel Immersion Gold
• Please: 0.8mm thickness
• Please: Add Break-up tab and Markpiont by yourself
• Recommend: Rotate the PCB 15 degrees
• Avoid: add any connection to the TF card plug when adding the margin (or you WILL HAVE A BAD TIME thinking how to remove the PCB margin)

These parts are optional, but recommended:

• A XTAL crystal for the MCU: improves the stability in bad working conditions
• A XTAL crystal for the HUB: some CH334P may not have the internal RC clock.
• All ESD-prevention parts: you don't want the ESD kill your device through the USB port/TF plug :)

These parts are not needed, unless in some special cases:

• The XTAL cristal for the TF reader: high speed/wont't work without it .

Building the Firmware

Use PlatformIO to build the firmware. Use the genericCH32V203G6U6/genericCH32V203C8T6 based on your version of the device.

Building the Software

If you want to use any other target, you can use the following command to build the software:

cargo build --release

In theory, the software should work on any platform which has the hidapi library, but only Linux is tested.

Debugging

For regular users, you can ignore this part.

The software provides control over individual GPIO pins, which can be used to debug the hardware. You can use the d or debug subcommand to control the GPIO pins. For example, you can use the following command to set the MUX_EN pin to high:

remo -i 0 d MuxEn 1

The following command can be used to check the current GPIO status:

remo -i 0 d AllStatus 0

An ACM uart port (115200 baud) is available for debugging using the USB-CDC port. You can use any serial terminal to connect to the port.

If you want to debug something earlier than the usb initialization, you can connect to the onboard serial port for the MCU using a USB-TTL adapter. Check the Hardware folder for the pinout. The serial port is using 115200 baud.

Inspiration

This project is inspired by following projects:

• usb sd mux - A commercial USB2.0 USB SD card switcher(not open source)
• SD Wire C - An open source USB2.0 SD card switcher
• usb sd mux fast - A commercial USB SD card switcher with USB3.0 support(not open source)
• AvaotaHyperCard - Manually controlled SD card

Contributors

Thanks to the following contributors for their contributions:

• Raaath Beeeee helped with the hardware debugging
• Queally rw helped with the hardware design and soldering
• Yao Zi ziyao@disroot.org helped with the hardware testing, and documentation
• And any other contributors who have contributed to this project.

Without their help, this project would not be possible :)

Copyright

Copyright (c) 2025 Wang Ling lingwang@wcysite.com. Copyright (c) 2025 Rath. All rights reserved.

License:

• Software part: Apache-2.0 (in folder Software)
• Hardware part: CERN-OHL-S-2.0 (in folder Hardware)
• Firmware part: GPL-3.0 (in folder Firmware)

(In my own understanding, communicating with the hardware part using any sort of communication protocol is not considered as a derivative work?)

Copyright Notice

We use the MIT-licensed library tinyusb. There're some optional changes in downstream.

The firmware framework is using PlatformIO and the wch chip support, they are all under Apache-2.0 license.

Thanks to pid.codes for the USB PID, which is under CC0 license.