Wheel speed measurement
An old forum discussion on this subject went along this line...
Bike wheel with magnet on spoke; reed switch operated by magnet; f-to-v converter gives voltage proportional to speed. (See attachments)
Your current A-D converter is looking for a varying voltage to represent speed, your reed switch will only jump from 0v to +5v (or whatever). You need to either count these pulses over a fixed time (or time betweeen pulses) or produce an analogue signal proportional to speed (the attached drawings).
The LM2917 circuit was tested as OK :wink: