How do I measure the revolutions of a moving object as it rotates around. Imagine a fan blade, I need to measure the rpm of the fan without using an outside tool such as a laser rpm reader. Ideally it would be a TINY chip attached to the fan blade. Does an accelerometer have this capability? Any ideas? Cheers!
You can attach magnets equally spaced to the center (1 would do the trick just fine too) and use the hall sensor to measure when the magnets pass near to it.
A few other ideals.
Let the fan strike a little object and measure the frequency of the strike noise.
Paint markers on the blade and measure reflected light intensity.
Put a pulley on the blade and an encoder on the other end.
Put a coil next to the outside of the blade and use the coil in an oscillator. The approoagig and leaving fan baalde will slow down and speed up the oscillator frequency output.