Thanks Arthur. Thats the thread I was referring to. On Tue, Jan 31, 2012 at 10:25 AM, Arthur Dent <[email protected]>wrote:
> >Tue Jan 31 14:15:57 UTC 2012 > >I did the mod and getting to pin 5 was tough. However Doug mentioned that > >there is another point to the left of the chip thats easier to get to. > >Don't recall the point. But if the lead ever comes off of 5 I can assure > >you I will find it. :-) > >My unit zeroed about at about 2 V. So I am using a 10 T 10 K bourns pot > >with 1000 counter. Then a 3.3V reg directly attached with bypass caps > >driven by 8 V from the regulated supply in the RB. > >Very clean, 3 leads into the RB. Using shielded cable through the pot hole > >that actually does nothing. > >Regards > >Paul. > +++++++++++++++++++++++++++++++ > > In case you missed it I had posted the information and a photo of the spot > to more easily solder the 100K resistor to give you EFC. I'd go with Bill > Riches' > suggestion to have the 100K in series with the EFC line. I connected the > lead > from the 100K to a pin on the DB-9 connector that was freed up when I put > the > 5V regulator inside so I could run off a single supply. Here's what I did. > > +++++++++++++++++++++++++++++++ > >Sun Jan 15 18:31:39 UTC 2012 > >I didn't solder the resistor directly to pin 5 of the IC. I found that > pin 5 > >was connected to a nearby SMD capacitor that was a little easier to > >solder to. Attached is a photo of the correct location if you want to try > >bringing the EFC out for analog control. > > http://farm8.staticflickr.com/7170/6702435071_f684967719_b.jpg > > > >Mon Jan 16 04:16:53 UTC 2012 > >I'm not sure what HEX number was loaded into my 5680A but the frequency > >was just slightly off from 10Mhz. Pin 5 on my 27M4BI quad opamp 'floats" > at > >2.599V and to get 10Mhz out it needs to be at 2.445V. I guess I could > correct > >the frequency digitally so it is at 10Mhz with pin 5 floating but I don't > feel it is > >necessary. The output frequency I measured with zero volts on pin 5 > (through > >the 100K resistor) was 10,000,000.028Hz and with 5V it was pretty close > to > >9,999,999.969Hz or .031Hz low so it's close to centered. I tried using a > 2K > >10-turn pot with about 10K on each side to restrict the tuning range > further and > >give me finer control. After the 5680A had been on for a while I tried > setting > >the frequency as close to 10Mhz as I could and watch the drift on my > scope > >using the 10Mhz Rb from my Datum 9390 GPS receiver as the reference. > >The 5680A seemed to stay within 5ns for 45 minutes so the resolution on > the pot > >is quite good and the 5680A seems quite stable. > > > >The pin 5 IC connection is the non-inverting input to the opamp and I'm > not > >sure if connecting the 100K resistor to the inverting input, pin 6, would > give > >you a positive change in frequency for a positive change in voltage or > not. > >If you're using a pot for adjustment or if the controller can be > programmed > >to change the polarity, it doesn't really make any difference and pin 5 > works > >just great. I'm glad Bill Riches found this input and posted the > information. > > -Arthur > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
