I stared to search with type of hardware I should use in this project. My natural choice was an arduino (maybe a tyniduino) since I need something lightweight that can be fixed on the glass rim.

However, since I was going to use audio I needed a microphone and sound processing features to record and audio file and send it to a STT engine. Therefore I choosed and Raspberry Pi Zero W, which can connect to the servo using the GPIO  and also allow a small USB microphone.

To power up the RPI Zero W I try some battery packs and other approaches, but all of them insert some extra weight in the glass that make it cumbersome and fatige factors when wering the glass for some time. 

My solution was simple: use the RPI Zero W fixed in the rim of the glass and connect the micro USB power cable to a powerbanl that should be stored inside a pocket of the user's pants. This way the weight of the power source is not on the user face.