[time-nuts] EFC tracking
didier at cox.net
Sat Jun 26 11:26:02 EDT 2010
I am commenting on my own comment :)
I have been using a similar kit from TI for the MSC1210Y5 processor (originally Burr-Brown, acquired by TI since). It was $50 and worked great. I have since made several projects at work using the chip.
Unfortunately, the MSC1210 kit is no longer available, but the new kit is even cheaper.
> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Didier Juges
> Sent: Saturday, June 26, 2010 10:20 AM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] EFC tracking
> You may want to check the "Analog Devices MiniKit for
> This kit includes a 24 bit ADC and integrated ARM processor
> in a small PWB with all the tools and sample code to do what
> you want with very little code to write (you can probably use
> the sample code as-is).
> The kit is $30 (or $35, depending on where you look...) and
> you will easily spend that much building something that will
> not work as well using your sound card.
> Sound card ADCs are intended for audio, and I'll bet their
> linearity does not come close to that of the ADuC702x series,
> if you can even get the spec for it.
> > -----Original Message-----
> > From: time-nuts-bounces at febo.com
> > [mailto:time-nuts-bounces at febo.com] On Behalf Of Steve Rooke
> > Sent: Saturday, June 26, 2010 7:13 AM
> > To: Discussion of precise time and frequency measurement
> > Subject: [time-nuts] EFC tracking
> > I would like to track the EFC voltage in hardware using something
> > cheap and ready to hand. I was thinking of using a sound card as it
> > has good resolution but it's obviously only AC coupled so
> it would not
> > measure the DC of the EFC. I thought about modifying a
> sound card to
> > make it DC coupled but most of them seem to reference the
> 0V point to
> > some internal reference voltage hence there is a DC shift there. I
> > next thought about turning the DC into AC by chopping it, IE.
> > inverting 50% of the voltage via an oscillator. This way I
> could pass
> > the square wave directly into an unmodified sound card, take
> > measurements and then do an RMS calculation on them (really
> just need
> > to flip the sign on, say, the negative readings).
> > I wonder if anyone has done something like this before and
> could share
> > their experiences. I've attached a diagram image (hope it
> is accepted
> > by the list) which is my first go with Eagle so I'm not
> exactly very
> > familiar with it, sorry. The R's and C's in the astable
> would be set
> > to a clock frequency that enables this to work without bias
> given the
> > sampling frequency. I'm not sure if this clock should be
> slower than
> > the sampling frequency or higher, just haven't got my head
> around that
> > yet. The R's around the op-amp would need to be set in a ratio that
> > transforms the EFC voltage into the range that the sound card can
> > handle (that is yet to be calculated by measuring the
> limits). If you
> > have any suggestions or ways of doing this in a better way, I'd be
> > very grateful for the advice.
> > Thanks,
> > Steve
> > --
> > Steve Rooke - ZL3TUV & G8KVD
> > The only reason for time is so that everything doesn't
> happen at once.
> > - Einstein
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