Author Topic: "Magic Numbers" Followup  (Read 1773 times)

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Offline anwTopic starter

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"Magic Numbers" Followup
« on: October 31, 2013, 12:32:33 PM »
I'm brand, spankin' new to this, didn't know whether to "Reply" to this:

About the “magic” numbers 25 and 44 on the photovore_v1.h file

or start a new topic; when I hit "Reply" at the above link, I was told in big, red letters I should start a new topic, so, if I've violated some protocol, please forgive me.

In this equation:

Code: [Select]
23/.992*(time in milliseconds) = number of cycles
I'd like to know from whence comes the 23/.992.  I've done a lot of searching on the site, and found this question asked twice, with the answer "From my oscilloscope."

But what are you measuring with the oscilloscope?  With an "on time" of 1 ms, 1.5 ms, and 2 ms and "magic numbers" of 25, 35, & 44, what this equation and its labels (milliseconds and cycles) imply to me is that you are varying some frequency between 25/1x10^-3, 35/1x10^, and 44/1x10-3, giving values of 25 KHz, 23.3 KHz, and 22.5 KHz, then applying some "fudge factor" (the 23/.992) that gives final answers of 580 KHz, 541 KHz, and 522 KHz.

All this assumes a 50% duty cycle, but I actually don't understand what's going on with these two numbers, the "23" and the ".992", at all.

What I just explained, though, is just using cycles and time to get a frequency, and there don't seem to be any units associated with the "fudge factor".

Sorry if this is elementary, and I'm not familiar with the processor and haven't done a deep dive into the source code.


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