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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!

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  • \$\begingroup\$ How would you wire to the TINY chip after all it is rotating? Why can't you use "an outside tool"? \$\endgroup\$ – Andy aka Feb 27 '17 at 13:45
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    \$\begingroup\$ You can always used a reed switch, hall effect sensor i.e. Outside tool. \$\endgroup\$ – ammar.cma Feb 27 '17 at 13:45
  • \$\begingroup\$ Have you even researched how this is done in fans, motors etc. ? Sure in the movies everything is possible by using a tiny chip. But in the real world, chips cannot perform magic (even though it might appears so to the uninitiated). What's so special about this TINY ? And how will you power it ? \$\endgroup\$ – Bimpelrekkie Feb 27 '17 at 13:52
  • \$\begingroup\$ Imagine a circle and two blades spinning around the circle, similar to a fan, but the middle of the fan is not moving. also my fan is 10 cm long. How can i measure the rpm using the smallest tool possible, and preferably this tool be attached to the middle of the fan. Forgive me for mu lack of research and knowledge, i thought i might come on here and ask people with the knowledge already, before conducting it myself. @an \$\endgroup\$ – Tynan Roussety Feb 27 '17 at 14:02
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    \$\begingroup\$ You probably could do it with an accelerometer if the fan is mounted vertically. The gravity vector will be rotating, plus a centripedal term because of rotation. You can make the board pretty small - square inch sized. But how will you power it, and what will you do with the data? Record it? Communicate it outside? \$\endgroup\$ – pjc50 Feb 27 '17 at 14:16
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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.

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A few other ideals.

  1. Let the fan strike a little object and measure the frequency of the strike noise.

  2. Paint markers on the blade and measure reflected light intensity.

  3. Put a pulley on the blade and an encoder on the other end.

  4. 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.

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