Shrub Hub USB Switch Interface

The Shrub Hub is a USB switch interface that enables a user to connect up to three 3.5 mm assistive switches to a digital device like a computer or mobile phone. It has five modes, and can send keystrokes, mouse clicks, and media control commands, with five outputs per mode. It is designed to provide digital access to people using assistive switches, and to be low cost and very easy to build.

Setup

Connect up to three 3.5 mm assistive switches into the Switch Adapter and then plug the Shrub Hub into a USB-A port on the computer or other digital device.

If only using one switch, the Shrub Hub can be used without the switch adapter, and the switch can be plugged directly into the Shrub Hub.

Usage

Each switch can be pressed to send a different keystroke, or multiple switches can be pressed at the same time to send a different keystroke than any of the individual buttons.

There are five different operating modes that each have their own unique sets of outputs. The operating mode can be changed by activating an assistive switch for 4 seconds.

A detailed User Guide is available at the Project Link or via the Download Link (requires log-in).

The Shrub Hub is designed to support individuals who experience difficulty using traditional computer input devices such as keyboards, mice, or touchscreens. This includes users with a wide range of motor, neuromuscular, and physical access challenges that limit fine motor control, hand strength, reach, or coordination. The Shrub Hub enables these users to operate digital devices using assistive switches.

This device may be particularly beneficial for people with:

• Limited hand mobility or dexterity, including those with conditions such as arthritis, cerebral palsy, muscular dystrophy, or spinal cord injuries.
• Reduced range of motion or difficulty performing precise movements, often experienced by individuals with neuromuscular disorders or chronic pain.
• Involuntary movements or tremors, making standard input devices difficult to use, such as in Parkinson’s disease or essential tremor.
• Upper-limb differences or amputation where traditional input tools are inaccessible or uncomfortable.
• Temporary impairments (injuries, surgeries, fatigue-related limitations) that require alternative access methods.

This device is specifically intended to be easy to build. The only skill needed is being able to 3D print parts, use a small screwdriver, and drag and drop files. There is optional customization that can be done if the maker is comfortable with minor software changes.

Note that this build does not require soldering.

This build involves assembling and programming the Shrub Hub and assembling the 3-to-1 Switch Adapter.

Assembling the Shrub Hub involves inserting the TRRS Trinkey into a 3D printed enclosure. Programming the Shrub Hub involves downloading the firmware, and dragging and dropping the firmware files into the Shrub Hub folder. Assembling the 3-to-1 Switch Adapter involves stripping wires and screwing them into a terminal, then inserting the terminal into a 3D printed enclosure.

This build does not require ordering custom PCBs or any soldering.

Detailed step-by-step instructions are available at the Project Link or via the Download Link (requires log-in).

CERN Open Hardware License - Weakly Reciprocal (OHL-W)