# [time-nuts] EFC tracking

WB6BNQ wb6bnq at cox.net
Sat Jun 26 13:21:42 UTC 2010

```Steve,

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.

Just set it for a 1KHz start point or maybe 10KHz.

Bill....WB6BNQ

Steve Rooke wrote:

> 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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```