Tap Strap 2 - Wearable Keyboard, Mouse & Air Gesture Controller
It includes 4 accelerometers, and a thumb IMU and haptic feedback device. The Optical Mouse might be an Optical Flow sensor, used both in mouses and drones to gauge ground speed. The Tap Strap has been around for some 4 years.
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This lady wearing a a violin does some impressive vocal multi-tracking, using the Tap Strap just to control Ableton. (control actions are noted in the upper-left)
It should work well for simple finger drumming (in mid air?) perhaps an invisible keyboard can be created as well, with a little training you can type text using their standard application.
They have an open source SDK with code in a few languages , I would probably translate their C# code to C++ for minimal latency in a ESP32 processor dealing with their raw sensor data. (the new cheaper ESP32-C3 may do)
They seem to be getting a lot our of their newer bracelet device as well.
The company has some 80 youtube videos.
Another simple example working with Garageband, playing little lamb. The IMU tied to the thumb should be able to track hand position change along the scale in mid-air, and along with the optical mouse on a table top.
The Tap Strap sells for $149, you can find them used on Ebay for $100.
Another form of input technology I ran across is a wrist mounted remote control (with one finger attachment) used to control cars and drones, it’s an option for a number of RC cars using Mechanum Wheels, popular in robotics for their ability to move sideways.
There’s a demo video on this sales page.
This guy made one with an Arduino 8 years ago.
A more rcent project, controlling a Starwars BB 8 with gestures.
Training a new user.