You can turn on an LED with a button or switch, but what about by bending your finger? Willpower Studios’ textile flex sensor, dubbed Finger Bend, presents a method for such an interface.
Inside the custom sleeve is a piece of piezoresistive stretch fabric, which is attached by copper threads to an Arduino Nano’s analog input pin. When a finger is curled, the light is then turned on and turned off again when straightened.
While an LED is interesting, this concept could be taken much further, perhaps using multiple digits for more intricate control. Details and code for the project is available in Willpower Studios’ write-up.