Giving a disabled person the ability to use a mouse and keyboard on a PC is one of the most important pieces of assistive technology we can create. Many disabled people use pushbuttons or other devices known as an AT Switch. These devices have a 3.5 mm mono jack on the end. One of the easiest ways to connect multiple switches to an assistive technology device is using the TRRS plug and jack. This gives us four conductors that we can connect to the microcontroller. In this circumstance, we have three buttons plus a common ground.

The TRRS Trinkey was specifically designed with assistive technology devices in mind. You can easily connect from 1 to 3 AT Switches to the device and use it for a variety of purposes. The great thing about this board is that it also has a STEMMA QT connector that allows us to connect other devices to the board. In this tutorial, we will connect a small OLED display that can be used as a virtual keyboard and mouse display. Using the AT Switches, a user can navigate a cursor around the display and type on a virtual keyboard. They can also move the mouse in any of eight directions, click any of the three mouse buttons, and operate the scroll wheel.

The TRRS Trinkey can also be connected to a phone or tablet with an OTG adapter to allow switch control access to touchscreen devices on iOS and many Android devices. The original learning guide for the TRRS Trinkey has a simplified switch control application in both Circuit Python and Arduino versions. However, here we will present an advanced version of the application for Arduino that allows you to use multiple simultaneous keypresses to get even more capability out of the device.