Phil Hobbs wrote:> > "Michael A. Terrell" wrote: > > > > Have you ever tried the foam in insulation, like 'Great Stuff', or > > would the chemicals it releases cause problems? > > I haven't used it for insulation except around pipes. My present house > had the main heating feed pipe to the bedroom end of the house cemented > into a concrete block wall for 20 feet, so I had to chisel it out and > add a combination of neoprene wrap and Great Stuff. (Now the inside of > the house gets warm instead of the outside.) ;) > > My main worries would be (a) it's ugly, (b) it's hard to control, and > (c) it's slow. I suppose you could squirt a bit into the bottom of a > greased tube, stick the whole works over the reference or XO, and clamp > it down to the board so the foam couldn't leak out the bottom. After a > day, remove the tube and trim the foam to size. > > I'd much sooner use styrofoam attached with RTV or hot melt.I was thinking about using it inside a shield, with a small hole in the lid to let the excess escape as it swells up. I am working on a GPS derived frequency standard, and looking into building a 10 MHz TCXO from scratch. I do have a couple open VCXO modules, without crystals that I could use as a starting point. http://www.ebay.com/itm/110892995725
LED reference current source
Started by ●September 9, 2012
Reply by ●September 12, 20122012-09-12
Reply by ●September 12, 20122012-09-12
On Wed, 12 Sep 2012 16:24:24 -0400, "Michael A. Terrell" <mike.terrell@earthlink.net> wrote:> >Phil Hobbs wrote: >> >> "Michael A. Terrell" wrote: >> > >> > Have you ever tried the foam in insulation, like 'Great Stuff', or >> > would the chemicals it releases cause problems? >> >> I haven't used it for insulation except around pipes. My present house >> had the main heating feed pipe to the bedroom end of the house cemented >> into a concrete block wall for 20 feet, so I had to chisel it out and >> add a combination of neoprene wrap and Great Stuff. (Now the inside of >> the house gets warm instead of the outside.) ;) >> >> My main worries would be (a) it's ugly, (b) it's hard to control, and >> (c) it's slow. I suppose you could squirt a bit into the bottom of a >> greased tube, stick the whole works over the reference or XO, and clamp >> it down to the board so the foam couldn't leak out the bottom. After a >> day, remove the tube and trim the foam to size. >> >> I'd much sooner use styrofoam attached with RTV or hot melt. > > > I was thinking about using it inside a shield, with a small hole in >the lid to let the excess escape as it swells up. I am working on a GPS >derived frequency standard, and looking into building a 10 MHz TCXO from >scratch. I do have a couple open VCXO modules, without crystals that I >could use as a starting point. http://www.ebay.com/itm/110892995725We made our own OCXO once. It was a thin PCB stuck to the top of an anodized aluminum block, with a mosfet heating the block. The crystal was embedded in the block. We cover it with a deep-drawn aluminum cover, 1.75" square and .625 high. We buy glass-packaged, vacuum-sealed crystals for this. They have a specified turning-point temperature of 60C, so the TC is almost zero there. https://dl.dropbox.com/u/53724080/Parts/Lap-Tech.JPG We tried putting foam inside the cover and it was no better than, maybe worse than, still air. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●September 12, 20122012-09-12
On Wed, 12 Sep 2012 14:19:40 -0700, John Larkin <jlarkin@highlandtechnology.com> wrote:>We tried putting foam inside the cover and it was no better than, >maybe worse than, still air.Want to try some really nice foam? It's about 5x better than urethane.
Reply by ●September 12, 20122012-09-12
On Wed, 12 Sep 2012 17:27:27 -0400, Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:>On Wed, 12 Sep 2012 14:19:40 -0700, John Larkin ><jlarkin@highlandtechnology.com> wrote: > > >>We tried putting foam inside the cover and it was no better than, >>maybe worse than, still air. > >Want to try some really nice foam? It's about 5x better than urethane.We tried a slab of styrafoam. Is your stuff better? -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●September 12, 20122012-09-12
On Sep 12, 7:16=A0pm, John Larkin <jlar...@highlandtechnology.com> wrote:> On Wed, 12 Sep 2012 09:30:27 -0700 (PDT),BillSloman > > > > > > > > > > <bill.slo...@ieee.org> wrote: > >On Sep 12, 5:40=A0pm, John Larkin > ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> On Wed, 12 Sep 2012 08:34:03 -0700 (PDT),BillSloman > > >> <bill.slo...@ieee.org> wrote: > >> >On Sep 12, 5:19=A0pm, John Larkin > >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> >> On Wed, 12 Sep 2012 08:43:28 -0400, Phil Hobbs > > >> >> <pcdhSpamMeSensel...@electrooptical.net> wrote: > >> >> >John Larkin wrote: > > >> >> >> On Wed, 12 Sep 2012 07:18:17 -0400, JW <n...@dev.null> wrote: > > >> >> >> >On Wed, 12 Sep 2012 03:46:57 -0700 (PDT)BillSloman > >> >> >> ><bill.slo...@ieee.org> wrote in Message id: > >> >> >> ><6bfd4cca-9e85-4ee8-990b-5c0049bce...@u15g2000yql.googlegroups.=com>:> > >> >> >> >>On Sep 12, 6:20 am, John Larkin > >> >> >> >><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: > >> >> >> >>> On Tue, 11 Sep 2012 20:30:47 -0700, josephkk > > >> >> >> >>> <joseph_barr...@sbcglobal.net> wrote: > >> >> >> >>> >On Tue, 11 Sep 2012 11:31:58 -0700, John Larkin > >> >> >> >>> ><jlar...@highlandtechnology.com> wrote: > > >> >> >> >>> >>>>>> When I put a light chopper on a laser and detect a we=ak> >> >> >> >>> >>>>>> response signal with a lock-in amplifier, the sensiti=vity will be> >> >> >> >>> >>>>>> much more clear. =A0Pay the extra nickel, use a REAL > >> >> >> >>> >>>>>> reference. =A0LM4140adj =A0is suitable, just add two > >> >> >> >>> >>>>>> resistors (the op amp is built in). > > >> >> >> >>> >>>>> I don't want a voltage reference, I want a low-capacit=ance current> >> >> >> >>> >>>>> source. > > >> >> >> >>> >>>> You are being disingenuous. > > >> >> >> >>> >>>> But you want a more or less stable current source, and =the> >> >> >> >>> >>>> compensating drifts of the LED and the transistor gives=the stable> >> >> >> >>> >>>> voltage that controls the current output. The transisto=r makes for a> >> >> >> >>> >>>> simpler, cheaper and more compact output than anything =fast enough/low> >> >> >> >>> >>>> capacitance enough for you that you could wrap around a=n LM4140.> > >> >> >> >>> >>>> If you needed something more accurate, you'd need a bet=ter reference> >> >> >> >>> >>>> voltage, but it seems that here you can get away with b=eing a> >> >> >> >>> >>>> cheapskate. > > >> >> >> >>> >>>Congratulations! You've just won this months SED Snarkies=t Way Of> >> >> >> >>> >>>Agreeing With Somebody Award. =A0This prestigious honour =is hotly> >> >> >> >>> >>>contested--it's almost as sought after as the Stupidest F=lame War Award.> > >> >> >> >>> >>>Cheers > > >> >> >> >>> >>>Phil Hobbs > > >> >> >> >>> >>Hey, it's only September 11. Give some other guys a chance=.> > >> >> >> >>> >You obviously think you can do better then. =A0Go for it of=you want.> > >> >> >> >>> >?-) > > >> >> >> >>> That wasn't very good;Slomanremains in the lead. > > >> >> >> >>John Larkin modestly - if incorrectly - underestimates his own > >> >> >> >>contributions. > > >> >> >> >"You are in a maze of twisty little IKYABWAIs, all alike" > > >> >> >> At least the current source seems to be very stable. > > >> >> >> LEDs do degrade in brightness over time. I wonder if their forwa=rd> >> >> >> voltage changes in any systematic way. > > >> >> >LED degradation is strongly associated with bad 1/f noise. (Lots o=f> >> >> >degradation mechanisms show 1/f behaviour, e.g. electromigration o=f> >> >> >interstitials and defect propagation.) =A0If you run the LEDs gent=ly, and> >> >> >check a few from the reel for bad 1/f, you should be okay for quit=e> >> >> >awhile. > > >> >> >Assuming the noise power predicts the aging rate, you could do an > >> >> >accelerated aging test and find out what Vf does with degradation.==A0It> >> >> >would be interesting to know whether the increased series resistan=ce or> >> >> >the enhanced nonradiative recombination dominates. > > >> >> >Cheers > > >> >> >Phil Hobbs > > >> >> Compound semiconductors, like gaasfets, have lots of crystal defect=s> >> >> and charge trapping sites. A gaasfet gate bias can jump by many > >> >> millivolts overnight. I'd suspect that forward voltage is less > >> >> sensitive to defects than gate bias. > > >> >The temperature sensitivity of forward bias does seem to be sensitive > >> >to the defect level > > >> >http://lib.semi.ac.cn:8080/tsh/dzzy/wsqk/SPIE/vol4776/4776-105.pdf > > >> >> But again, this application isn't > >> >> very critical. I'm charging a ramp capacitor that's feeding two > >> >> comparators, then a flipflop. It's sort of a 200 picosecond 555 tim=er.> > >> >I can see the current source driving a capacitor and two comparators, > >> >but I doubt if there's a direct connection to the flip-flop. Flip- > >> >flops don't like slow edges. > > >> The comparators feed the flop, of course. As I said, it's sort of like > >> a 555. > > >from Hamlet > > >"Hamlet: Do you see yonder cloud that's almost in shape of a camel? > >Polonius: By th' Mass, and 'tis like a camel, indeed. > >Hamlet: Methinks it is like a weasel. > >Polonius: It is backed like a weasel. > >Hamlet: Or like a whale. > >Polonius: Very like a whale. " > > >It's a pity that Shakespeare couldn't anticipate the 555. > > I mostly only like the comedies. We just saw "Two Gentlemen" at the > Tahoe Shakespeare Festival, on the Nevada side of Lake Tahoe, on a > peninsula jutting out into the lake, at dusk. Stunning, recommended to > anyone who can make it. We had Adirondack chairs (and blankets!) near > the stage and our own waiter for food and drinks. Things like that are > fun, now and then. > > We sort of adopted the single guy sitting next to us, bought him wine > and loaned him a blanket. Turns out he teaches English and Shakespeare > at UofN in Reno and knows the cast and the touring gossip. Fun. > > I think my favourite movie of all time is 12th Night, the one with > Imogen Stubbs and Ben Kingsley and Helena Bonham Carter.When we lived in England I was signed up for the Royal Shakespeare Company's subscription list. We'd see a couple of plays a year, mostly at the Barbican, though we went to Stratford at least once. It's more comfortable indoors. -- Bill Sloman, Nijmegen
Reply by ●September 12, 20122012-09-12
On Wed, 12 Sep 2012 14:55:21 -0700 (PDT), Bill Sloman <bill.sloman@ieee.org> wrote:>On Sep 12, 7:16�pm, John Larkin <jlar...@highlandtechnology.com> >wrote: >> On Wed, 12 Sep 2012 09:30:27 -0700 (PDT),BillSloman >> >> >> >> >> >> >> >> >> >> <bill.slo...@ieee.org> wrote: >> >On Sep 12, 5:40�pm, John Larkin >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> On Wed, 12 Sep 2012 08:34:03 -0700 (PDT),BillSloman >> >> >> <bill.slo...@ieee.org> wrote: >> >> >On Sep 12, 5:19�pm, John Larkin >> >> ><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> >> On Wed, 12 Sep 2012 08:43:28 -0400, Phil Hobbs >> >> >> >> <pcdhSpamMeSensel...@electrooptical.net> wrote: >> >> >> >John Larkin wrote: >> >> >> >> >> On Wed, 12 Sep 2012 07:18:17 -0400, JW <n...@dev.null> wrote: >> >> >> >> >> >On Wed, 12 Sep 2012 03:46:57 -0700 (PDT)BillSloman >> >> >> >> ><bill.slo...@ieee.org> wrote in Message id: >> >> >> >> ><6bfd4cca-9e85-4ee8-990b-5c0049bce...@u15g2000yql.googlegroups.com>: >> >> >> >> >> >>On Sep 12, 6:20 am, John Larkin >> >> >> >> >><jjlar...@highNOTlandTHIStechnologyPART.com> wrote: >> >> >> >> >>> On Tue, 11 Sep 2012 20:30:47 -0700, josephkk >> >> >> >> >> >>> <joseph_barr...@sbcglobal.net> wrote: >> >> >> >> >>> >On Tue, 11 Sep 2012 11:31:58 -0700, John Larkin >> >> >> >> >>> ><jlar...@highlandtechnology.com> wrote: >> >> >> >> >> >>> >>>>>> When I put a light chopper on a laser and detect a weak >> >> >> >> >>> >>>>>> response signal with a lock-in amplifier, the sensitivity will be >> >> >> >> >>> >>>>>> much more clear. �Pay the extra nickel, use a REAL >> >> >> >> >>> >>>>>> reference. �LM4140adj �is suitable, just add two >> >> >> >> >>> >>>>>> resistors (the op amp is built in). >> >> >> >> >> >>> >>>>> I don't want a voltage reference, I want a low-capacitance current >> >> >> >> >>> >>>>> source. >> >> >> >> >> >>> >>>> You are being disingenuous. >> >> >> >> >> >>> >>>> But you want a more or less stable current source, and the >> >> >> >> >>> >>>> compensating drifts of the LED and the transistor gives the stable >> >> >> >> >>> >>>> voltage that controls the current output. The transistor makes for a >> >> >> >> >>> >>>> simpler, cheaper and more compact output than anything fast enough/low >> >> >> >> >>> >>>> capacitance enough for you that you could wrap around an LM4140. >> >> >> >> >> >>> >>>> If you needed something more accurate, you'd need a better reference >> >> >> >> >>> >>>> voltage, but it seems that here you can get away with being a >> >> >> >> >>> >>>> cheapskate. >> >> >> >> >> >>> >>>Congratulations! You've just won this months SED Snarkiest Way Of >> >> >> >> >>> >>>Agreeing With Somebody Award. �This prestigious honour is hotly >> >> >> >> >>> >>>contested--it's almost as sought after as the Stupidest Flame War Award. >> >> >> >> >> >>> >>>Cheers >> >> >> >> >> >>> >>>Phil Hobbs >> >> >> >> >> >>> >>Hey, it's only September 11. Give some other guys a chance. >> >> >> >> >> >>> >You obviously think you can do better then. �Go for it of you want. >> >> >> >> >> >>> >?-) >> >> >> >> >> >>> That wasn't very good;Slomanremains in the lead. >> >> >> >> >> >>John Larkin modestly - if incorrectly - underestimates his own >> >> >> >> >>contributions. >> >> >> >> >> >"You are in a maze of twisty little IKYABWAIs, all alike" >> >> >> >> >> At least the current source seems to be very stable. >> >> >> >> >> LEDs do degrade in brightness over time. I wonder if their forward >> >> >> >> voltage changes in any systematic way. >> >> >> >> >LED degradation is strongly associated with bad 1/f noise. (Lots of >> >> >> >degradation mechanisms show 1/f behaviour, e.g. electromigration of >> >> >> >interstitials and defect propagation.) �If you run the LEDs gently, and >> >> >> >check a few from the reel for bad 1/f, you should be okay for quite >> >> >> >awhile. >> >> >> >> >Assuming the noise power predicts the aging rate, you could do an >> >> >> >accelerated aging test and find out what Vf does with degradation. �It >> >> >> >would be interesting to know whether the increased series resistance or >> >> >> >the enhanced nonradiative recombination dominates. >> >> >> >> >Cheers >> >> >> >> >Phil Hobbs >> >> >> >> Compound semiconductors, like gaasfets, have lots of crystal defects >> >> >> and charge trapping sites. A gaasfet gate bias can jump by many >> >> >> millivolts overnight. I'd suspect that forward voltage is less >> >> >> sensitive to defects than gate bias. >> >> >> >The temperature sensitivity of forward bias does seem to be sensitive >> >> >to the defect level >> >> >> >http://lib.semi.ac.cn:8080/tsh/dzzy/wsqk/SPIE/vol4776/4776-105.pdf >> >> >> >> But again, this application isn't >> >> >> very critical. I'm charging a ramp capacitor that's feeding two >> >> >> comparators, then a flipflop. It's sort of a 200 picosecond 555 timer. >> >> >> >I can see the current source driving a capacitor and two comparators, >> >> >but I doubt if there's a direct connection to the flip-flop. Flip- >> >> >flops don't like slow edges. >> >> >> The comparators feed the flop, of course. As I said, it's sort of like >> >> a 555. >> >> >from Hamlet >> >> >"Hamlet: Do you see yonder cloud that's almost in shape of a camel? >> >Polonius: By th' Mass, and 'tis like a camel, indeed. >> >Hamlet: Methinks it is like a weasel. >> >Polonius: It is backed like a weasel. >> >Hamlet: Or like a whale. >> >Polonius: Very like a whale. " >> >> >It's a pity that Shakespeare couldn't anticipate the 555. >> >> I mostly only like the comedies. We just saw "Two Gentlemen" at the >> Tahoe Shakespeare Festival, on the Nevada side of Lake Tahoe, on a >> peninsula jutting out into the lake, at dusk. Stunning, recommended to >> anyone who can make it. We had Adirondack chairs (and blankets!) near >> the stage and our own waiter for food and drinks. Things like that are >> fun, now and then. >> >> We sort of adopted the single guy sitting next to us, bought him wine >> and loaned him a blanket. Turns out he teaches English and Shakespeare >> at UofN in Reno and knows the cast and the touring gossip. Fun. >> >> I think my favourite movie of all time is 12th Night, the one with >> Imogen Stubbs and Ben Kingsley and Helena Bonham Carter.Don't edit my text. HBC was OK, but I meant Imelda Staunton.> >When we lived in England I was signed up for the Royal Shakespeare >Company's subscription list. We'd see a couple of plays a year, mostly >at the Barbican, though we went to Stratford at least once. It's more >comfortable indoors.Before I moved to CA, I visited SF and decided to have a look at the UC Berkeley campus. There was a line outside a building, so I got into line. It was the Oxford Shakespeare Company doing Midsummer Night's. The stage was a bare wooden oval, nothing else but a couple of ropes hanging down from above, and the actors were all clad in fetish leathers. They were awfully good. I decided to move here. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●September 12, 20122012-09-12
In article <deu1589j4ca1lm8vudvlfq46v8nmqhl198@4ax.com>, John Larkin <jlarkin@highlandtechnology.com> writes:>We made our own OCXO once.Why? Cheaper? Better? Strange packaging? -- These are my opinions. I hate spam.
Reply by ●September 12, 20122012-09-12
On Wed, 12 Sep 2012 14:37:10 -0700, the renowned John Larkin <jlarkin@highlandtechnology.com> wrote:>On Wed, 12 Sep 2012 17:27:27 -0400, Spehro Pefhany ><speffSNIP@interlogDOTyou.knowwhat> wrote: > >>On Wed, 12 Sep 2012 14:19:40 -0700, John Larkin >><jlarkin@highlandtechnology.com> wrote: >> >> >>>We tried putting foam inside the cover and it was no better than, >>>maybe worse than, still air. >> >>Want to try some really nice foam? It's about 5x better than urethane. > >We tried a slab of styrafoam. Is your stuff better?Way better. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Reply by ●September 12, 20122012-09-12
On Sep 12, 11:19=A0pm, John Larkin <jlar...@highlandtechnology.com> wrote:> On Wed, 12 Sep 2012 16:24:24 -0400, "Michael A. Terrell" > > > > > > > > > > <mike.terr...@earthlink.net> wrote: > > >Phil Hobbs wrote: > > >> "Michael A. Terrell" wrote: > > >> > =A0 =A0Have you ever tried the foam in insulation, like 'Great Stuff=', or> >> > would the chemicals it releases cause problems? > > >> I haven't used it for insulation except around pipes. =A0My present ho=use> >> had the main heating feed pipe to the bedroom end of the house cemente=d> >> into a concrete block wall for 20 feet, so I had to chisel it out and > >> add a combination of neoprene wrap and Great Stuff. =A0(Now the inside=of> >> the house gets warm instead of the outside.) ;) > > >> My main worries would be (a) it's ugly, (b) it's hard to control, and > >> (c) it's slow. =A0I suppose you could squirt a bit into the bottom of =a> >> greased tube, stick the whole works over the reference or XO, and clam=p> >> it down to the board so the foam couldn't leak out the bottom. =A0Afte=r a> >> day, remove the tube and trim the foam to size. > > >> I'd much sooner use styrofoam attached with RTV or hot melt. > > > =A0I was thinking about using it inside a shield, with a small hole in > >the lid to let the excess escape as it swells up. =A0I am working on a G=PS> >derived frequency standard, and looking into building a 10 MHz TCXO from > >scratch. =A0I do have a couple open VCXO modules, without crystals that =I> >could use as a starting point.http://www.ebay.com/itm/110892995725 > > We made our own OCXO once. It was a thin PCB stuck to the top of an > anodized aluminum block, with a mosfet heating the block. The crystal > was embedded in the block. We cover it with a deep-drawn aluminum > cover, 1.75" square and .625 high. > > We buy glass-packaged, vacuum-sealed crystals for this. They have a > specified turning-point temperature of 60C, so the TC is almost zero > there. > > https://dl.dropbox.com/u/53724080/Parts/Lap-Tech.JPG > > We tried putting foam inside the cover and it was no better than, > maybe worse than, still air.The point about foam is that it is mostly air, but the cell structure stops the air from moving. Double-glazing works the same way - a 6mm gap between the panes is enough to suppress convection currents. Bigger gaps are better for sound insulation, but degrade thermal insulation because the convection currents can circulate fast enough to shift a significant amount of heat. -- Bill Sloman, Nijmegen
Reply by ●September 12, 20122012-09-12
On Wed, 12 Sep 2012 19:09:28 -0400, Spehro Pefhany <speffSNIP@interlogDOTyou.knowwhat> wrote:>On Wed, 12 Sep 2012 14:37:10 -0700, the renowned John Larkin ><jlarkin@highlandtechnology.com> wrote: > >>On Wed, 12 Sep 2012 17:27:27 -0400, Spehro Pefhany >><speffSNIP@interlogDOTyou.knowwhat> wrote: >> >>>On Wed, 12 Sep 2012 14:19:40 -0700, John Larkin >>><jlarkin@highlandtechnology.com> wrote: >>> >>> >>>>We tried putting foam inside the cover and it was no better than, >>>>maybe worse than, still air. >>> >>>Want to try some really nice foam? It's about 5x better than urethane. >> >>We tried a slab of styrafoam. Is your stuff better? > >Way better. > > >Best regards, >Spehro PefhanyAerogel? Zillion layer mylar superinsulator in vacuum? The real way to do a good OCXO is a double oven. -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
