The encoders we needed for this project weren't available, so Richard made some:

Ideal for small robots and motor control applications, this small sensor board measures the orientation of a nearby magnet (contactless measurement). It uses an SPI interface for communications, and can return angle values to 14bit precision – that’s 16384 counts per revolution, or 0.022° degrees.

Its tiny 21mm x 17mm dimensions mean it will fit any project, and can be easily mounted even to tiny motors or actuators using the 2.2mm holes.

They are now available on Tindie