Instant Interrupts - Revisited

[HankMcSpank]

Hank,

I need to wire up a variable phase shifter, so that I can compare my results with yours. Not sure why you can't read below 33 deg? Maybe phase locking between the two comparators or interupt house keeping? What happens if you halve the frequency?

It all works well above a certain phase shift (depending on the signal frequency)...just when you get to the lower regions that this quirk kicks in.

I'm sure you're sorted for a phase shift cct, there's a simple one here....

http://www.werewoolf.org.je/graphics/apf1.gif

....make R1 & R2 the same value -I used 10k - the cap about 100nf & R4 a 10k pot (wired with the wiper to the ground end)....this gives about 90 degrees of phase shift @ 159Hz...if you want more phase shift,cascade a few together & use this designer http://www.aleph.co.jp/~takeda/radio/psDesigner.swf

just be sure that the signals into your PIC comparator are identical (I square them up first - remember ...different edge 'slopes' equals different triggering points for the PIC comparators which translates into a phase measurement error - and I also check on a scope to make sure there aren't any edge timing errors intrduced prior to the PIC)

If I half the incoming frequency (or double it), the Comp2 count remains the same (ie it won't go below 336, as I phase shift to the lower regions)...so I'm inclined to think it's housekeeping 'can't avoid' timing issue of some sort.

there maybe one fly in my particular ointment - my PIC supply is 4V...the datasheet says that 4.5V is the minimum when using a 20Mhz External clock. (& annoyingly, I don't appear have any 5V regulators handy so now looking at dropping the clock back to 8Mhz)

I look forward to your results so get a move on!