frequency mesurement of a square wave

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hamid 2015-2-22

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评论： Image Analyst 2018-6-24

采纳的回答： Image Analyst

hi I want to to measure the frequency of a square wave with simulink , do anybody know how to do this? thanks

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Image Analyst 2015-2-22

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编辑：Image Analyst 2015-2-22

在 MATLAB Online 中打开

I don't have Simulink but I think you can use a MATLAB block in it where you run MATLAB code. If so, then just threshold the signal and use find()

signal = [0 0 6 6 6 0 0 6 6 6 0 0 6 6 6 0 0]
halfMaxValue = 0.5 * (min(signal) + max(signal)) % Halfway between 0 and 6.
highSignals = signal > halfMaxValue
diffSignal = [0 diff(highSignals)]
diffSignalIndexes = find(diffSignal == 1)
period = diffSignalIndexes(2) - diffSignalIndexes(1) % Distance between first two pulses.

In the command window:

halfMaxValue =
     3
highSignals =
     0     0     1     1     1     0     0     1     1     1     0     0     1     1     1     0     0
diffSignal =
     0     0     1     0     0    -1     0     1     0     0    -1     0     1     0     0    -1     0
diffSignalIndexes =
     3     8    13
period =
     5

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Image Analyst 2015-2-24

Your signal doesn't quite look right. The plot seems to show it going high around element 43 or 44 but your signal variable shows it going up around element 42.

hamid 2015-2-24

bravo ! my simulink solver was incorrect, I corrected it and got the right answer 5 Hz. very very very thanks <3

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MoeIsKing 2018-6-24

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https://ww2.mathworks.cn/matlabcentral/answers/179673-frequency-mesurement-of-a-square-wave#answer_326045

编辑：Image Analyst 2018-6-24

在 MATLAB Online 中打开

scope_15.csv

If i run:

highSignals = signal > halfMaxValue

over my signal i get:

"Error using horzcat
Dimensions of arrays being concatenated are not consistent."

What did i wrong? My "highSignals" type is "2002x1 logical" after I run:

highSignals = volts > halfMaxValue ;

halfMaxValue is 12 and volts comes from a scope (light bar) and is imported as csv into "2002x1 double"

It looks OK to me. What I don't understand is how you could execute the line to create highSignals successfully as a 2002 by 1 vector, and yet still have an error thrown? In my experience if an error is thrown, you will not get the result put into the output variable. Can you explain that? Exactly what line of code are you executing when the error is thrown?

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