For my GCSE Engineering project, I am building a device which attaches to the frame of a bike, and uses a magnet (Attached to the wheel) to detect 1 turn of the wheel (I have also compensated for contact bounce etc.) The only problem I face is that I have never used reed switches before, and I don't know what sensitivity of reed switch to use.
Assuming the bike wheel is 2150mm circumference, the max speed is 13 m/s, the magnet diameter is 50mm and it will be 180mm from the centre of the wheel, I calculated that (hopefully) the smallest amount of time the switch will be directly passing the magnet is 0.0037 seconds.
I thought this seemed like a very small amount of time for a switch to close and open again before 1 rotation is over. A 1AT switch apparently closes at the north pole from the earth itself, so just to be safe i want to avoid disaster from it being too sensitive. Does anyone know what type/sensitivity of reed switch to use?