I resisted the suggestion to use Twinkies for insulation (and ate them!), plus tossed out all the other 'good' suggestion for modifications like using a robotic arm to move a magnet to trim the frequency, and used a very simple modification that I just completed a few minutes ago; and it seems to be working well. On the inside of the case where the DB-9 pins go through the circuit board, I mounted a 7805 fixed regulator. I cut a piece out of pin 4 and connected the output of the 7805 to the board side of the pin with a tantalum cap for bypass. I decided not to use a 78L05 because at the elevated temperature I felt it would be cutting it too close to the 100MA current limit. I then soldered a wire to the connector side of pin 4 and ran it through the center heatsink to pin 5 of the IC next to the ribbon connector (in series with a 100K ohm resistor) as described by Bill Riches on Thu Dec 22 22:00:40 UTC 2011. Pin 4 now 'floats' at 2.5V and can be connected to an external 10-turn pot adjustable from 0-5V to trim the frequency, or to a DAC for EFC.
So the 5680 I have can now be adjusted externally by a 0-5V signal and it requires just the single 15V supply. And for the penny-pinchers, the added parts cost well under $3. ;-) A photo of the regulator before I connected the wire to pin 4 on the connector is at the link below. http://farm8.staticflickr.com/7013/6668466093_90782cf7e9_b.jpg -Arthur _______________________________________________ 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.