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Increasing precision of Input Capture...

 
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ELCouz



Joined: 18 Jul 2007
Posts: 427
Location: Montreal,Quebec

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Increasing precision of Input Capture...
PostPosted: Fri Feb 20, 2015 7:01 pm     Reply with quote
Hi,

I've been reading and trying to modify the CCS example (ex_capture.c) to give me frequency instead of period lengths in uS.

However, i'm not very experienced with this kind of area.

I'm trying to read the frequency of a small flow meter (YF-S401)

The equation is according to the flow meters spec is:

Code:

Frequency: F = 98 * Q (Q is flow L / min) error: ± 5% 5880 pulse per liter of water

Frequency calculation = constant * unit flow (L / min) * time (seconds)

Flow Range :0.3-6L / min


I tried converting period to hz but I get garbage values every time...


Code:

printf("\r\r%1.9f Hz",(((float32)Time*64)/100000));


This what I've modified in the example but it's wrong.

I have a scope and the Freq range of the flow meter is 0 to 200 hz

Any clue?
_________________
Regards,
Laurent

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temtronic



Joined: 01 Jul 2010
Posts: 9134
Location: Greensville,Ontario

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PostPosted: Fri Feb 20, 2015 8:18 pm     Reply with quote
Are you using the sensor as the input for testing? If so, I wouldn't.
Instead, either use 1/2 wave and full wave line frequency (60Hz and 120Hz, here in Canada, eh !) as two test frequencies OR use a second PIC as the 'frequency generator' with say 25, 50, 100, 150, 200 Hz as outputs on 5 pins.
Simple delay_ms() should be good enough' for test loops.
This way you KNOW what the input is and can then pull your hair out 'getting the math' right.

hth
Jay
ELCouz



Joined: 18 Jul 2007
Posts: 427
Location: Montreal,Quebec

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PostPosted: Fri Feb 20, 2015 8:33 pm     Reply with quote
temtronic wrote:
Are you using the sensor as the input for testing? If so, I wouldn't.
Instead, either use 1/2 wave and full wave line frequency( 60Hz and 120Hz ,here in Canada,eh !) as two test frequencies OR use a second PIC as the 'frequency generator' with say 25,50,100,150,200 Hz as outputs on 5 pins.
Simple delay_ms() should be good enough' for test loops.
This way you KNOW what the input is and can then pull your hair out 'getting the math' right.

hth
Jay


I see the value live on my scope and I can tell you it's not good Smile

But I found out that it's better and easier just to count the pulses to know how many mL have passed thru!

Thanks!
_________________
Regards,
Laurent

-----------
Here's my first visual theme for the CCS C Compiler. Enjoy!
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