For example, the feedback from an optical rotary encoder can be used to accurately determine the current position of each individual pivot joint of a robotic arm. Using this data, a controller can ...

Commercial shaft encoders use magnets and Hall-effect sensors, or optical sensors and encoder discs. But these can be quite expensive, so [Hello1024] hacked together an alternative in an afternoon.

He ended up exploring hard drive motors as encoders, and while the results aren’t exactly high resolution, he may be onto something. Starting with a teardown of some old HDDs — save those magnets!

In devices which use rotary knobs, the AS5601 and its paired magnet may replace a rotary encoder without any change to the host microcontroller or its application software.