Measuring audio phase shift through a circuit with a PIC

[HankMcSpank]

I haven't checked your code, but, from the description, I think you need to look at it differently to get the correct results. Try it this way.

enable comparator1 and 2 interrupts

when comparator1 interrupts,
clear timer1
clear timer2
start timer1 and timer 2 running

when comparator1 interrupts again, do the following....

stop timer1 running & store the 'count' (this gives a clock pulse 'count' for the arriving frequency, but since I'm only after phase shift...which is a time based measurement, I don't calculate the frequency)

when comparator2 interrupts, stop timer2 & store the count

Thanks for you input....seems reasonable - I'll be revisiitng this tonight (last night I got waylaid trying to get PIC to control a digital pot via SPI .....failed - http://www.picbasic.co.uk/forum/show...3540#post93540 )

Using your revised approach, I reckon to calculate the phase change it's this....

time lag (ie phase difference) = timer2 - timer1

then to work out the phase ....time lag x 360/timer1/


So an example, lets say timer1 = 2000 & timer2 = 2,200

this would give a difference (time lag) of 200 clock pulses

Now bearing in mind timer1 = 360 degrees (one complete cycle)

Therefore to establish out how many single degrees of phase...

200 * 360 /2000 ....which means in this example the phase shift is a 36 degrees lag.


Putting that into actual frequency ....

clock = 2us
one 'wave' period = 2000 x 2us = 4ms
In Hertz = 1/0.004 = 250hz

time lag of second waveform = 200 x 2us = 400us

Now being lazy, to verify, using an online phase calculator & inputing 250Hz & a lag time of 400us...

http://www.sengpielaudio.com/calcula...delayphase.htm

= 36 degrees.