The fourth feature is a choice between Azoteq’s waterproof inductive button or the inductive force sensing. The waterproof button uses an inductive sensing coil on the PCB to detect the movement of a metal object through the housing. This allows you to seal off all electronics on the inside of the housing while still detecting the deflection of a metal button on the outside to produce a function.
Force sensing, however, happens when the user squeezes the housing of the application to produce the desired action – such as the play or pause of music in earbuds. Force sensing is a popular user interface for TWS applications, as it is not prone to false activations when the earbud is handled or put down on a table. It is also a more robust and reliable interface than capacitive sensing in applications that tend to get wet or damp, such as earbuds that are used in more active lifestyles.
Competing force-sensing techniques are based on capacitive sensing, while Azoteq uses inductive technology. When the housing is compressed, the sensor detects the decrease in distance between a target and an inductive coil or SMT inductor on the PCB to produce an output. The sensor can be calibrated to trigger an action only when a certain amount of pressure is exerted, allowing manufacturers to achieve repeatability in manufacturing. The method also allows designers to completely seal in electronics to design a waterproof solution that is aesthetically pleasing, without seams, buttons, or apertures.