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