[time-nuts] EFC tracking

[Steve Rooke]

Bill,

On 27 June 2010 01:21, WB6BNQ <wb6bnq at cox.net> wrote:
> 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.

I just had one of those duh! moments :) It does make the sampling a
little more complicated as I'd have to take a number of samples and do
something like a FFT to get the frequency, I think. My idea seemed
just a simple way to just make a single, or limited number, of
sample(s) and I have the data. Still, this is a good idea and I'll
have a good thunk about it.

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

Thanks for your advice,
Steve

> 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
>>
>>   ------------------------------------------------------------------------
>>                  Name: DCchop.png
>>    DCchop.png    Type: PNG image (image/png)
>>              Encoding: base64
>>
>>   ------------------------------------------------------------------------
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



-- 
Steve Rooke - ZL3TUV & G8KVD
The only reason for time is so that everything doesn't happen at once.
- Einstein