This question is related to Is it possible to “trace” a hall effect sensor on a PCB?.
As far as I understand it, a Hall effect sensor consists of a metal plate, plus a current source and an amplifier.
Instead of buying a Hall effect sensing chip, would it be possible to implement this with a PCB and a microcontroller? A metal plate is easy to come by within a PCB, and current sources, amplifiers and ADCs are available in some microcontrollers (e.g. PSoC4)
Applications for this might include current sensing in a power supply, or position sensing of a magnet.
One drawback might be that the size of the plate would have a poor tolerance. Are there any other reasons this wouldn't be possible?