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RE: [avr-gcc-list] How to accurately measure a square wave frequency


From: Rune Christensen
Subject: RE: [avr-gcc-list] How to accurately measure a square wave frequency
Date: Fri, 22 Oct 2004 10:44:08 +0200

Hello

Have you looked at the capture system of the timer. The timer should be able
to create a timestamp for the pos edge and neg edge of the signal. 

     |-----------|                  |-----------
     |           |                  |
-----|           |------------------|
    old         new                new
    pos         neq                pos

newpos_timestamp - oldpos_timestamp = 1/frequency

newneq_timestamp / (newpos_timestamp - oldpos_timestamp) = duty cycle


Best regards
Rune Christensen

> -----Original Message-----
> From: address@hidden 
> [mailto:address@hidden On Behalf Of system default
> Sent: Friday, October 22, 2004 10:26 AM
> To: address@hidden
> Subject: [avr-gcc-list] How to accurately measure a square 
> wave frequency
> 
> 
> Hi all,
> My name is Joe, I am new to the list and AVR-GCC.
> I am using an ATMega32, and would like to measure a
> pulse on a pin. I was originally using a basic compiler
> that had a high level function called PulseIn.
> This function returned the time in 10uS ticks of the
> high and low parts of the square wave.
> 
> I need something smilar to this so i can calculate the 
> frequency. I have never used AVR-GCC before so I am 
> unsure how to do this. I am using a 4Mhz crystal, If I use
> a loop of some sort with a delay of 10uS how much error 
> will the code overhead cause? Does anyone already have
> a method to determin the frequency of a pulse?
> Or know a good method to do this?
> 
> Note: It must work on a range from ~100Hz to ~60kHz
> 
> Thank you very much.
> 
> -Joe
> 
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> http://www.avr1.org/mailman/listinfo/avr-gcc-list
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