Adafruit TRRS Trinkey Simplifies Adding Assistive Technology Switches to Projects

Adafruit has added a new member to the Trinkey family of development boards. The TRRS Trinkey is a USB-based board that combines a 3.5-millimeter headphone TRRS breakout with a USB-native microcontroller. This compact integration seamlessly connects Assistive Technology (AT) switches to a USB-capable host computer.

The TRRS Trinkey's board measures 42.0 by 15.0 by 6.5-millimeter with a 3.5-millimeter phone jack on one side and a USB-A plug. It has a Microchip ATSAMD21E18 microcontroller with an Arm Cortex-M0+ core running at 48 MHz, 32 KB of SRAM, and 256 KB of flash. There is also an Adafruit STEMMA QT connector, which allows you to connect a diverse set of peripherals such as temperature sensors, accelerometers, or OLED displays.

TRRS plugs have four contacts broken out: tip, ring 1, ring 2, and sleeve. Adafruit wired those four contacts to GPIO pins on the SAM D21 microcontroller. Additionally, they have connections to the tip and ring 1, which you can use to detect when a device is plugged in. You can use the microcontroller to change each TRRS contact to be an input, connected to ground, or source 3.3 volts.

The TRRS Trinkey microcontroller does not run a specific firmware. Instead, you can program it with the Arduino IDE or CircuitPython to function as a USB HID device (keyboard or mouse) for a PC. Both options make converting inputs from an AT switch (or potentiometer) into programmable actions straightforward.

Eagle design files can be found in this GitHub repository. Alternatively, you can buy a pre-made board for $9.95 from the Adafruit TRRS Trinkey product page.