how to measure the angle
Hello trail_hehe,
Could you please elaborate a bit more on your application?
The encoder could work if the mass of the pendulum and accelerations are enough as to overcome encoder friction, and you have a rigid link between pendulum bob and fulcrum.
With reed type magnetic sensors you could only detect the presence of the pendulum's bob in a certain position, but hardly measure an angle.
Optical sensors share the same characteristics, but they will not damp the movement as could be the case with mag sensors.
There are magnetic sensors with an analog output mesuring distance from sensor to object, but I don't know if the precision is enough for you application.
Hope this helps.