UPC EETAC Bachelor's Degree in Telecommunications Systems and in Network Engineering EEL

Chapter 2 problems

     - D2.23 -

Button decoder for music earbuds




1. Specifications

Design the button decoder (button_controller) that is typical in most commercial Bluetooth earbuds. The idea is to assign a binary code to each function once detected.

Typical functions

Fig. 1. Example earbuds. Only one tactile or conventional button is available for commanding operations.

Once paired, depending on the apps selected in the mobile phone, earbuds can be used for answering phone calls, voice assistance or playing music. Let us simplify to Fig. 2 where only typical music player functions are listed.


Fig. 2. Example especifications when used as music player.

An internal switch S may be used to select left or right earbuds. For example S = '0' is the right earbud, S = '1' is the left earbud.

The idea is organise a FSM to detect one, two or five continuous short clicks, and also a long press. Fig. 3 shows a block diagram of an earbud from Toshiba company.

Button controller

Fig. 3. Block diagram of an earbud. Reference paper: wireless earphone solution for long time operation with a small battery on a wireless earphone. TVS stands for transient voltage suppressor diodes to prevent the destruction of the electronics due to electrostatic discharges (ESD). LDO is a low dropout voltage regulator.  

Experiment in a protoboard and characterise the signals from a typical push-button. What is the typical time duration of a short and a long pulse?

Probably, a debouncing filter is required to generate clean pulses.