Build A Digital Tachometer/RPM Counter

Questions and Comments on All Tutorials

KansaiRobot
Newbie Pyro
Posts: 2
Joined: Fri Apr 24, 2015 8:53 am

Build A Digital Tachometer/RPM Counter

Postby KansaiRobot » Wed Sep 02, 2015 3:02 am

In the tutorial of the title, part 3 there is the following equation to calculate RPM

Image

I don't understand this formula. Can someone explain it to me?

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I got the lower part. (Period*7). To complete a total revolution you need 7 pulses so it is clear that the total period for one revolution would be (Period*7).
I guess since we are looking for RPM (minute) we put the 60 seconds in the upper part.

What I dont understand is:

1) Why putting the other part (1/Fosc*4)?

2) If a instruction takes 4 cycles, you would have to divide not multiply by 4, won't you?


Any help greatly appreciated

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