“Human-machine interface” (HMI) is a general term that describes any physical input or output hardware that people can use to interface with systems (like computers) and vice versa. That very broad definition usually applies to computer input devices like keyboards or output devices like monitors. The move towards touchscreens represented a fundamental shift in HMI preferences and we might see another shift soon towards wearable HMIs. To provide the building blocks of that potential future, a team of UCLA engineers developed this wearable, waterproof, wireless HMI.

This prototype HMI is a patch that users can wear on their skin and that resembles a thick Band-Aid. It flexes and stretches along with the user’s skin, making it comfortable to wear for extended periods of time. The prototype has four buttons that can wirelessly control remote devices. In the team’s demonstration, for example, the buttons control a music player’s functions. It is also waterproof, so users don’t have to worry about damage from sweat or other moisture.

The underlying technology for this HMI relies on electromagnetic induction. Each button is a small coil and the silicone patch material has embedded micromagnets. When a user presses a button, the coil moves in the magnetic field and induces a small electrical signal. Similarly, the natural flex and stretch of the path caused by user movement generates a small amount of power. With further development, that might even be enough power to make batteries or an external power source unnecessary.

For the time being, the team turned to Arduino to demonstrate the concept. Leads from the button coils connect to the ADC (analog-to-digital converter) of an Arduino Uno board through an amplifier and filter circuit. The Arduino converts those signals into digital signals and then transmits them through an HC-05 Bluetooth module. A receiver unit consisting of another Uno and HC-05 then controls the connected device, such as a music player or lamp.