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Frequency Measurement Using CCP2 Module

 
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arup
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Frequency Measurement Using CCP2 Module
PostPosted: Tue Apr 08, 2008 10:41 pm     Reply with quote
Dear Sir,
Pls help on following query.

Application : Frequency Measurement Of half wave rectangular wave form of frequency 20 Hz to 80 Hz.

Hardware : PIC18F6585 . Crystal OSC . 20 MHz. The above mentioned signal is fed to ccp2 pin(pin no 40)

Pls note Micro circuit is battery backed up.

Development Tools : CCS C COMPILER

Method : I have used CCP2 module and timer3 as time base for this.

Code:

setup_ccp2(CCP_CAPTURE_RE); // Configure CCP2 to capture rising edge
setup_timer_3(T3_INTERNAL|T3_DIV_BY_8|0x08); // Start timer 3 ,prescaler  /8 ,
enable_interrupts(INT_CCP2); // Setup interrupt on rising edge     


In interrupt routine,
On first rising edge I have reset the timer3 . and on next rising edge I have taken CCP2 register value. So this will be my timer counter(16 bit) between two rising edge.
From the above details we can calculate timer3 frequency = 625000 Hz.
Code:
#define  FREQ_CONST  625000L 

1) so Frequency of subjected waveform = (unsigned char)(FREQ_CONST / timer counter )
Is this above method is OK ? any betterment using CCP2 module only.?

2) When power goes off , the signal at micro ccp2 pin will be at low state. Supposing that just before power gets off micro has detected a rising edge and reset the timer3 .Now micro will not get a rising edge until power comes .So I can’t update frequency(let’s say in last calculation frequency was 49 Hz) .But I have to detect the frequency .

To solve this ……
I have created a 10ms time base using timer0.At every 10 ms I will increment a counter
Code:

Void  f1_10ms(){

Zxcntr++;

}

I will reset that counter whenever there is rising edge found.In case of power goes off this counter will not reset .So I will check 5 such count i.e 50 ms and conclude that frequency is zero and reset that counter.

Is this method correct and reliable ? Could anybody suggest me for any better method ?

Regards,

Arup
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Tue Apr 08, 2008 11:12 pm     Reply with quote
There are several threads on using the CCP to find the frequency.
Just search for:
Quote:

tachometer

Here is the search page link:
http://www.ccsinfo.com/forum/search.php
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