[time-nuts] PICPET- was Affordable (cheap) COTS (etc)

[Azelio Boriani]

It seems that that the QEI on a dsPIC are internal hardware counters
decoding the A/B phases of optical encoders: are you sure that they
can be used like a time interval counter? Better to use the timer
capture dedicated input.

On Thu, Jan 23, 2014 at 12:31 PM, Anders Wallin
<anders.e.e.wallin at gmail.com> wrote:
> Given that Arduinos are now sold in (almost) every super-market, and the
> programming IDE is free/open-source, and the C/C++ code is familiar to
> many, I would have thought the logical evolution of the "pictic" is to
> become an Arduino shield?
>
> One drawback (AFAIK) is that e.g. Arduino Due doesn't have a dedicated
> counter/encoder input, like the dsPICs made for motor-control have.
> On the other hand the Due has 12-bit analog inputs (and DACs) that might
> work for interpolation.
>
> How fast can the QEI (quadrature encoder interface) on a dsPIC clocked at
> 140MHz count? Were you planning on using a dsPIC with two QEIs, for TIC
> start&stop coarse counting?
> For 1ns or 2ns resolution an analog (or fpga?) interpolator is required
> anyway?
>
> AW
>
>
> On Thu, Jan 23, 2014 at 4:10 AM, Tom Van Baak (lab) <tvb at leapsecond.com>wrote:
>
>> Hi Bob,
>>
>> It's pretty easy to get a tiny PIC or AVR down to 50 ns, so to me the next
>> sweet spot would be 1 or 2 ns. A couple of us are trying. Contact me
>> off-list re the dsPIC33.
>>
>> /tvb (i5s)
>>
>> > On Jan 22, 2014, at 5:53 PM, Bob Stewart <bob at evoria.net> wrote:
>> >
>> > Tom,
>> >
>> > Do you know of any other PIC projects that get a greater resolution?  I
>> was thinking of doing something with a dsPIC33 running at 140MHz or
>> greater, but I'm not sure I want to devote the time to if it's it's been
>> done.
>> >
>> > Bob
>> >
>> >
>> >
>> >
>> >> ________________________________
>> >> From: Tom Van Baak (lab) <tvb at leapsecond.com>
>> >> To: Robert Atkinson <robert8rpi at yahoo.co.uk>; Discussion of precise
>> time and frequency measurement <time-nuts at febo.com>
>> >> Sent: Wednesday, January 22, 2014 7:39 PM
>> >> Subject: Re: [time-nuts] Affordable (cheap) COTS / eBay kit for TIE /
>> 1PPS phase comparison
>> >>
>> >>
>> >> As much as I'm fond of my picPET it has 400 ns resolution and not
>> intended to replace a 5 or 10 or 50 ns TIC (which is what the OP asked for).
>> >>
>> >> /tvb (i5s)
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