Reply by John Larkin May 12, 20172017-05-12
On Fri, 12 May 2017 11:23:10 +0200, o pere o <me@somewhere.net> wrote:

><snip> > >> >> DPOTS are slow, too. Trimpots are usable at a GHz or so. > >Hmmm, for pots I recall a thumb rule of f x R < 1E6... I would have >thought that perhaps a small, low R trimpot might be usable at 100MHz. >Did you really got them working as expected at 1 GHz? > >Pere
Yes, we've tested trimpots up there. Most pots have a convoluted geometry inside, that adds capacitance and inductance. Some tiny pots are more sensible. This Bourns pot has the convoluted geometry https://dl.dropboxusercontent.com/u/53724080/Parts/Resistors/Bourns_Pot_2.jpg and this 7-cent Murata part https://dl.dropboxusercontent.com/u/53724080/Parts/Resistors/Tiny_Pot.JPG doesn't. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by o pere o May 12, 20172017-05-12
<snip>

> > DPOTS are slow, too. Trimpots are usable at a GHz or so.
Hmmm, for pots I recall a thumb rule of f x R < 1E6... I would have thought that perhaps a small, low R trimpot might be usable at 100MHz. Did you really got them working as expected at 1 GHz? Pere
Reply by piglet May 12, 20172017-05-12
On 09/05/2017 22:20, Phil Hobbs wrote:
> Trouble is, all the trim pots I can find are ~200 cycles rated > rotational life, or not rated at all. >
If you think their skills are adequate you could use through hole trimpots in TO-5 sockets or whatever suitable socket you find and a bag of spare trimpots with instructions on how to swap trimpots when worn! piglet
Reply by George Herold May 11, 20172017-05-11
On Thursday, May 11, 2017 at 6:52:03 PM UTC-4, Spehro Pefhany wrote:
> On Thu, 11 May 2017 08:24:11 -0700 (PDT), the renowned George Herold > <gherold@teachspin.com> wrote: > > >On Thursday, May 11, 2017 at 3:57:39 AM UTC-4, Spehro Pefhany wrote: > >> On Wed, 10 May 2017 16:40:05 -0700 (PDT), the renowned George Herold > >> <gherold@teachspin.com> wrote: > >> > >> >We use a lot of those too. 1" diameter hole for pot=20 > >> >(trim off plastic tabs on pot) > >> >and ~1/4" hole centered (somewhere) on the 1" circumference=20 > >> >for the solder tabs. > >> > >> Next time get slots! Way stronger and easier to solder. > >> > >> https://i.imgur.com/4DWYbKz.png > >> > >> --sp > >> > >> -- > >> Best regards, > >> Spehro Pefhany > > > >Hi Spehro, not sure what that is. (Maybe I'm misunderstanding.) > >I meant this, > > > >https://www.dropbox.com/s/hir1owa5sjpeb4q/DSCN9663.JPG?dl=0 > > > >Which looks like a used a 3/8" hole on the perimeter. > > > >George H. > > Ah, I thought you were putting a board onto the pot to make > connections to it. Pretty common technique in some quarters- a little > transition board with a connector.
Oh well maybe, I thought Phil was sticking a big ass pot through a pcb. Doesn't matter. I'm mostly an idiot when it comes to mechanical layout. On my first instrument, (for money rather than one-of's in labs.) I used those pots at right angles from front panel to pcb, but didn't mechanically secure the alignment enough... (Forget shake machines, just mail packages to yourself via UPS.) When ~50% (or so.) were broken on arrival we had to change things. George H.
> > --sp > > -- > Best regards, > Spehro Pefhany
Reply by John Larkin May 11, 20172017-05-11
On Thu, 11 May 2017 18:52:08 -0400, Spehro Pefhany
<speffSNIP@interlogDOTyou.knowwhat> wrote:

>On Thu, 11 May 2017 08:24:11 -0700 (PDT), the renowned George Herold ><gherold@teachspin.com> wrote: > >>On Thursday, May 11, 2017 at 3:57:39 AM UTC-4, Spehro Pefhany wrote: >>> On Wed, 10 May 2017 16:40:05 -0700 (PDT), the renowned George Herold >>> <gherold@teachspin.com> wrote: >>> >>> >We use a lot of those too. 1" diameter hole for pot=20 >>> >(trim off plastic tabs on pot) >>> >and ~1/4" hole centered (somewhere) on the 1" circumference=20 >>> >for the solder tabs. >>> >>> Next time get slots! Way stronger and easier to solder. >>> >>> https://i.imgur.com/4DWYbKz.png >>> >>> --sp >>> >>> -- >>> Best regards, >>> Spehro Pefhany >> >>Hi Spehro, not sure what that is. (Maybe I'm misunderstanding.) >>I meant this, >> >>https://www.dropbox.com/s/hir1owa5sjpeb4q/DSCN9663.JPG?dl=0 >> >>Which looks like a used a 3/8" hole on the perimeter. >> >>George H. > >Ah, I thought you were putting a board onto the pot to make >connections to it. Pretty common technique in some quarters- a little >transition board with a connector. > >--sp
Here's an encoder mounted on a baby board. https://dl.dropboxusercontent.com/u/53724080/PCBs/Encoder_Board.jpg The four spacers are also the electrical connections. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by Spehro Pefhany May 11, 20172017-05-11
On Thu, 11 May 2017 08:24:11 -0700 (PDT), the renowned George Herold
<gherold@teachspin.com> wrote:

>On Thursday, May 11, 2017 at 3:57:39 AM UTC-4, Spehro Pefhany wrote: >> On Wed, 10 May 2017 16:40:05 -0700 (PDT), the renowned George Herold >> <gherold@teachspin.com> wrote: >> >> >We use a lot of those too. 1" diameter hole for pot=20 >> >(trim off plastic tabs on pot) >> >and ~1/4" hole centered (somewhere) on the 1" circumference=20 >> >for the solder tabs. >> >> Next time get slots! Way stronger and easier to solder. >> >> https://i.imgur.com/4DWYbKz.png >> >> --sp >> >> -- >> Best regards, >> Spehro Pefhany > >Hi Spehro, not sure what that is. (Maybe I'm misunderstanding.) >I meant this, > >https://www.dropbox.com/s/hir1owa5sjpeb4q/DSCN9663.JPG?dl=0 > >Which looks like a used a 3/8" hole on the perimeter. > >George H.
Ah, I thought you were putting a board onto the pot to make connections to it. Pretty common technique in some quarters- a little transition board with a connector. --sp -- Best regards, Spehro Pefhany
Reply by George Herold May 11, 20172017-05-11
On Thursday, May 11, 2017 at 3:57:39 AM UTC-4, Spehro Pefhany wrote:
> On Wed, 10 May 2017 16:40:05 -0700 (PDT), the renowned George Herold > <gherold@teachspin.com> wrote: > > >We use a lot of those too. 1" diameter hole for pot=20 > >(trim off plastic tabs on pot) > >and ~1/4" hole centered (somewhere) on the 1" circumference=20 > >for the solder tabs. > > Next time get slots! Way stronger and easier to solder. > > https://i.imgur.com/4DWYbKz.png > > --sp > > -- > Best regards, > Spehro Pefhany
Hi Spehro, not sure what that is. (Maybe I'm misunderstanding.) I meant this, https://www.dropbox.com/s/hir1owa5sjpeb4q/DSCN9663.JPG?dl=0 Which looks like a used a 3/8" hole on the perimeter. George H.
Reply by Spehro Pefhany May 11, 20172017-05-11
On Wed, 10 May 2017 16:40:05 -0700 (PDT), the renowned George Herold
<gherold@teachspin.com> wrote:

>We use a lot of those too. 1" diameter hole for pot=20 >(trim off plastic tabs on pot) >and ~1/4" hole centered (somewhere) on the 1" circumference=20 >for the solder tabs.
Next time get slots! Way stronger and easier to solder. https://i.imgur.com/4DWYbKz.png --sp -- Best regards, Spehro Pefhany
Reply by May 11, 20172017-05-11
On Wednesday, May 10, 2017 at 7:17:57 AM UTC+10, Phil Hobbs wrote:
> Hi, all, > > I'm doing a lab special for some folks in the physics department of the > University of Oxford. It's an interesting wrinkle on the laser noise > canceller, which is going to work with some HgCdTe photodiodes at 5 > microns. (*) > > These gizmos are probably significantly less linear than silicon diodes, > so I'm giving them an offset current adjust pot so that they can tweak > the cancellation point a little bit. Thus they're going to be adjusting > that pot quite often. > > Trouble is, all the trim pots I can find are ~200 cycles rated > rotational life, or not rated at all.
http://www.farnell.com/datasheets/1911177.pdf No specified rotational life, but much more settable than cheaper parts. I remember specifying a similar part for the Cambridge Instruments electron beam microfabricator. It was more expensive than the part it replaced, but the fact that you could set it precisely meant that final test saved about half an hour on getting the board set up - everybody ended up pleased about that. -- Bill Sloman, Sydney
Reply by George Herold May 10, 20172017-05-10
On Tuesday, May 9, 2017 at 10:19:08 PM UTC-4, pcdh...@gmail.com wrote:
> >Bourns 3590 ten-turn WW pots are not as expensive as one might fear. > >Rotational life is listed at 10^6 turns, and tempco is 50ppm/&deg;C. > > Nice parts, I agree. I don't have a panel to mount them on, but since I have a 200k resistor between the pot and anything sensitive, I might be able to make a big hole in the board to mount the pot.
We use a lot of those too. 1" diameter hole for pot (trim off plastic tabs on pot) and ~1/4" hole centered (somewhere) on the 1" circumference for the solder tabs. George H.
> > Thanks > > Phil Hobbs