[time-nuts] EFC tracking

Didier Juges 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.
 
Didier 

> -----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
> 
> Steve,
> 
> You may want to check the "Analog Devices MiniKit for 
> ADuC702x-series".
> 
> http://www.google.com/search?q=Analog+Devices+MiniKit+for+ADuC
> 702x-series
> 
> 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.
> 
> Didier 
> 
> > -----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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