Hi This isn't my design originally. The 620 ohm resistor in question sources current into a diode stack. The initial current will vary more from the tolerance of the diodes than it will from the 1 ohm change ( or 6 ohm = 1%).
The other resistor sets the range on two pots. The pot's tolerance is >= 5x the resistor's. The new value will give you slightly more adjustment range in some cases. The simple answer really is that the values for 5% and 1% resistors are different. This being the world that it is, you can get 1%'s in 5% values. I switched systems to find available parts. The other simple answer is that the accuracy of the design comes more from pot twiddling than from initial resistor values. Bob On Aug 13, 2010, at 11:34 PM, "Heathkid" <heath...@heathkid.com> wrote: > Bob, > > Thanks for the update! How critical are the values of the components? If > I'm going to build this (actually six of them)... I'd prefer to do it right > (and best) the first time. Going from a 620ohm 1% to a 619ohm is probably > negligible. But if it's design is *supposed* to require a 620ohm 1% 50ppm > metal film resistor then shouldn't that be what I should get (even if I have > to get it from a different source)? Maybe I'm being *really* picky here... I > do tend to take things to **extremes**. Even the people I work with get > frustrated sometimes with me because when I build things... I tend to match > resistors, caps, inductors, etc. to within 0.001% of what the design > specifies. Yes... I've bought 400 resistors for a headphone amplifier just > to find two that were matched perfectly (even at temperature changes - 0C to > 40C). > > Also, when building... can the standard IC's be socketed - I like it that way > (I'm sure the PIC is okay)? I know that affects some circuits. Do you know > if this will have any effect on the operation or accuracy of the PICTIC II? > If it's okay... standard or machine pin (if it makes a difference). > > And finally... *what* should the input/output connectors be? Thanks again! > > 73 Brice KA8MAV > > > ----- Original Message ----- From: "Bob Camp" <li...@rtty.us> > To: "Discussion of precise time and frequency measurement" > <time-nuts@febo.com> > Sent: Friday, August 13, 2010 5:34 PM > Subject: Re: [time-nuts] What's the latest correct PICTIC II Mouser project?- > Heathkid > > >> Hi >> >> Shortages... what shortages :)......? >> >> The two offending resistors have been "bumped" to 1% standard values from 5% >> standard. Functionally there should be no difference at all. >> >> Sorry for the delay in getting it up dated. >> >> Bob >> >> >> On Aug 13, 2010, at 1:47 AM, Heathkid wrote: >> >>> Hello everyone. I received my six (6) PICTIC II PCBs which are absolutely >>> beautiful (after a couple minutes of standard cleaning with a pencil eraser >>> which I do anyway to *any* PCB* I order) and I was getting ready to place >>> my order for the components tonight but the following (in the "latest >>> project") are now "back ordered" with estimated shipping dates of like >>> October! Any suggestions for equal or superior parts? Please? Does anyone >>> have an updated "Mouser Project" that has all the "correct" or better >>> quality parts in stock (equal to or better quality that spec'd)? >>> >>> Here's what I've been trying to work with thanks to Bob Camp. >>> Unfortunately, two of the components are now not available... help??? >>> >>> https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=8736DCEE10 >>> >>> Mouser #: 271-620-RC >>> Metal Film Resistors - Through Hole 620ohms 1% 50PPM >>> >>> Mouser #: 271-2.4K-RC >>> Metal Film Resistors - Through Hole 2.4Kohms 1% 50PPM >>> >>> I'd like to place the complete order for all the components for my six >>> PICTIC II's as quickly as possiible. >>> >>> Thanks, >>> 73 Brice KA8MAV >>> >>> _______________________________________________ >>> 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. > > > _______________________________________________ > 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.
