[time-nuts] EFC tracking
jdb at lartmaker.nl
Sat Jun 26 13:15:51 EDT 2010
At 01:43 +1200 27-06-2010, Steve Rooke wrote:
> > I don't know if it qualifies as simple/cheap, but Analog Devices and others
>> have single chip low-rate sigma/delta converters with good to excellent
> > properties; these were meant for strain gauges but should be able to track
> > slow-moving control voltages just fine. [...]
>Do you have any part numbers to hand that I could go and look up
(You didn't specify runtime or resolution; I am assuming that you
plan to monitor an OCXO CV line over several days; this would imply
that you're interested in sub-mV wiggles on a constantish offset of a
few V. Do set me straight if I'm wrong)
I was looking at the Microchip MCP355x-series and Cirrus
CS551x-series. Both are available in DIY-friendly SOIC-packages; if
you can handle SOT-23-6 and TSSOPs your choices widen (ie the AD778x
that Jim Lux mentioned). Both families are S/D converters with
internal digital filtering, offering 20+ bit resolution (although not
all bits are usable, depending on your config).
Most of these parts are available from Farnell and Digi-Key (and if
it were me, I'd order from the latter).
At 10:20 -0500 26-06-2010, Didier Juges wrote:
>You may want to check the "Analog Devices MiniKit for ADuC702x-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
Seconded, but note that according to the datasheet it only offers an
internal 12-bit ADC (although the docs from AD seem to contradict
eachother here). This may be Good Enough. The advantage of the
ADuC7xxx series over most other microcontrollers with built-in ADCs
is that the ADuC7xxx ADC has a differential input mode. For more
cheap boards, have a look at Olimex (http://www.olimex.com/dev/).
At 06:21 -0700 26-06-2010, WB6BNQ wrote:
>I think using a voltage-to-frequency converter would solve that problem. They
>are not too expensive and there are several flavors from Amalog
>devices and some others.
Good idea, but might be hard to keep stable enough if my "sub-mV over
days"-assumption is right.
Years from now, if you are doing something quick and dirty,
you imagine that I am looking over your shoulder and say to
yourself, "Dijkstra would not like this," well that would be
immortality for me. -- Edsger Dijkstra, 1930 - 2002
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