On Sun, 5 Apr 2020 17:54:54 -0700 (PDT), whit3rd <whit3rd@gmail.com> wrote:>On Sunday, April 5, 2020 at 5:12:12 PM UTC-7, jla...@highlandsniptechnology.com wrote: >> On Sun, 5 Apr 2020 12:43:27 -0700 (PDT), plastcontrol.ru@gmail.com >> wrote: >> >> >NXP 74aup2g07 - analog switch >> >https://assets.nexperia.com/documents/data-sheet/74AUP2G07.pdf >> >> Those are great. I use them to discharge the cap in precision >> linear-ramp timing circuits. > >The traditional way to discharge the cap would be a controlled current source, and >you take the zero-crossing time to indicate the state of charge instead of using >a fast ADC. That way, all cycles discharge the capacitor to the exact same level.I don't design from tradition. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Favourite parts with off-label uses?
Started by ●April 4, 2020
Reply by ●April 6, 20202020-04-06
Reply by ●April 6, 20202020-04-06
On Mon, 6 Apr 2020 11:13:48 +1000, Clifford Heath <no.spam@please.net> wrote:>On 6/4/20 10:12 am, jlarkin@highlandsniptechnology.com wrote: >> On Sun, 5 Apr 2020 12:43:27 -0700 (PDT), plastcontrol.ru@gmail.com >> wrote: >> >>> NXP 74aup2g07 - analog switch >>> https://assets.nexperia.com/documents/data-sheet/74AUP2G07.pdf >> >> Those are great. I use them to discharge the cap in precision >> linear-ramp timing circuits. > >I know you're concerned about the C-V curve with your fast ramps. How >does this device stack up (against your fave pHEMTs for example)> > >Clifford HeathA timing ramp doesn't need to be especially linear. Polynomial calibration is easy. It does need low jitter and low tempco and not ring much. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●April 6, 20202020-04-06
On Saturday, April 4, 2020 at 8:49:22 PM UTC-4, pcdh...@gmail.com wrote:> Following up on blocher's sterling work,(*) > > Many of us use parts off-label, often very successfully. A few examples: > > SAV-551+ pHEMTs make very good wideband bootstraps. Their f_max is around 12 GHz, but they're amazingly stable. > > 74HC4352s make good flying-capacitor diff amp front ends. > > TMUX1511s make very nice analogue lock-ins--their Coff*Ron FOM is almost in a class with relays, but 1E5 times faster. > > Zero-ohm jumpers have about the right resistance to stabilize LDO regulators with ceramic output caps. (It's good to be able to disconnect the supplies during bring-up, and putting the jumper between the reg and the output cap has this additional benefit. > > Your faves? > > Cheers > > Phil Hobbs > (*) who may be bulegoge's good twin, given the similarity of their emails ;)o CMOS gates for power supplies, precision voltage switching, class-C r.f. power amps. o Various semiconductor junctions as varicaps. o I'm still searching for a way to use crappy ceramic caps as varactors. Tuning a WWVB loop antenna might finally be that chance. o LEDs as detectors. Cheers, James Arthur
Reply by ●April 6, 20202020-04-06
On 2020-04-05 13:39, jlarkin@highlandsniptechnology.com wrote:> On Sun, 5 Apr 2020 12:17:03 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 2020-04-05 11:42, jlarkin@highlandsniptechnology.com wrote: >>> On Sun, 5 Apr 2020 10:52:29 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 2020-04-05 00:09, jlarkin@highlandsniptechnology.com wrote: >>>>> On Sat, 4 Apr 2020 17:49:18 -0700 (PDT), pcdhobbs@gmail.com wrote: >>>>> >>>>>> Following up on blocher's sterling work,(*) >>>>>> >>>>>> Many of us use parts off-label, often very successfully. A few >>>>>> examples: >>>>>> >>>>>> SAV-551+ pHEMTs make very good wideband bootstraps. Their f_max is >>>>>> around 12 GHz, but they're amazingly stable. >>>>> >>>>> They make excellent switches too. Rds-on is never specified for RF >>>>> parts, but it's about 2 ohms for the 551. >>>>> >>>>>> >>>>>> 74HC4352s make good flying-capacitor diff amp front ends. >>>>>> >>>>>> TMUX1511s make very nice analogue lock-ins--their Coff*Ron FOM is >>>>>> almost in a class with relays, but 1E5 times faster. >>>>>> >>>>>> Zero-ohm jumpers have about the right resistance to stabilize LDO >>>>>> regulators with ceramic output caps. (It's good to be able to >>>>>> disconnect the supplies during bring-up, and putting the jumper >>>>>> between the reg and the output cap has this additional benefit. >>>>>> >>>>>> Your faves? >>>>> >>>>> Some digital bus and USB switches are cheap and are excellent, >>>>> super-fast analog multiplexers. >>>>> >>>>> Some chips are useful just for their ESD diodes. >>>>> >>>>> LVDS line receivers are super-fast, dirt cheap RRIO comparators. >>>> >>>> I've used them like that at your suggestion. Snazzy if you don't need >>>> super low offset voltage. (And if you do, every comparator slows way down.) >>>> >>>>> >>>>> An LED can be used as the voltage reference for an NPN current >>>>> source. The tempcos can be made to almost cancel. >>>>> >>>>> High value AlN resistors can be used as thermal bridges. >>>> >>>> That's interesting. I recall discussing some very expensive parts sold >>>> specifically for DC isolating thermal pours. >>>> >>>>> >>>>> Surface-mount platinum RTDs can be used in experiments, as both >>>>> heater and sensor, to quantify resistor heat sinking and thermal >>>>> transients. >>>>> >>>>> Surface-mount resistors can be last-resort fuses. >>>>> >>>>> Low-barrier schottky diodes can be used in reverse as >>>>> constant-current things. Tempcos are not great. The same diode can >>>>> charge and discharge a capacitor. >>>> >>>> Interesting. Are they reasonably repeatable unit-to-unit? >>> >>> For modest values of reasonable. It's Is, which is huge for >>> schottkies, hundred nA sorts of numbers. I've posted my RF detector >>> which is a diode and a capacitor. It's in production. >>> >>>> >>>>> >>>>> Some self-protecting SSRs can be used as electronic fuses. As can a >>>>> 3t regulator with the adj pin open. >>>>> >>>>> Depletion fets are nice capacitor bleeders. Ditto 3t reg as a >>>>> current sink. >>>> >>>> >>>>> >>>>> A bit of open-load transmission line can be a high-frequency peaker. >>>>> I have that option in my GHz o/e layout. >>>> >>>> Interesting. How does that work? Normally I think of O/C tlines as a >>>> series resonance to ground. >>> >>> Stick a drooling-rise step into one end of a transmission line and it >>> will overshoot and snap up the waveform at the other end. Adjust the >>> source impedance, or terminate a little, to trim the step response. >>> It's sharper than RC peaking, so compensates things like Ft rolloff or >>> skin effect. >> >> Okay, so not really open-circuited. I'll try it out. That could >> potentially have helped that single-diode sampler gizmo--its speed was >> limited by the rise time of the line receiver driving the pHEMT switch. >> That one used a capacitor plus a short, mismatched shunt stub to make >> the sampling pulse from a falling edge. > > The soft peaking helps when a step has a soft corner on the rise, > which is very common. That's why people who do fast stuff cheat and > measure risetime 20/80. > >> >>> >>> I had a profound, life-changing revelation recently. If you don't poke >>> a fast rise into a passive transmission line, you won't get a fast >>> reflection. I wasted all those years designing absorptive lowpass >>> filters. >> >> Gasp! ;) >> >>> >>>> >>>> >>>>> >>>>> Someone said never use an opamp as a comparator. They were wrong. >>>> >>>> Gotta watch for the antiparallel diodes on the inputs, though. For slow >>>> stuff, LM358s work great as comparators--the inputs survive going way >>>> above the supply. >>>> >>>>> >>>>> An rro opamp can also be used as a current limiter/fuse. >>>>> >>>>> You can do all sorts of things with ribbon cable. >>>>> >>>>> Some HV diodes and the c-b junctions of some transistors make >>>>> awesome drift step-recovery (Grehkov) diodes. >>>>> >>>>> BFT25s can be used as fA-leakage diodes. >>>>> >>>>> Dual-winding inductors, like DRQ127, can do all kinds of tricks. >>>> >>>> Annoying that they don't tell you k in the datasheet, and you can't even >>>> back it out from the series-connected inductance, which is quoted as >>>> exactly four times the parallel-connected value. >>> >>> The k's are really high. Easy to measure. >> >> That's unusual for a 'coupled inductor'. I normally expect it to be >> around 0.85. > > The DRQs are bifilar. Two or three 9's. > > And a lot of capacitance. They make nice autotransformer flybacks. > Does that have a better name? > > > >>>>> A toroidal inductor can be a liquid level sensor. >>>> >>>> That one I haven't heard about. Are you looking for the NMR signal? ;) >>> >>> A conductive liquid is a shorted turn. >> >> At sufficiently low frequency, anyway. >> >> We've started putting little Sensirion T/H sensors in a lot of things. >> When using TECs, it's awfully nice to be able to compute the dew point, >> for instance, and in outdoor applications (e.g. our fire sensors for >> harvesters) it's good to be able to predict when the window is liable to >> fog up on the inside. >> >> We use IP67+ enclosures with bags of 5A molecular sieve inside, which is >> super cheap and will absorb 50% of its own mass in water. Simon has had >> to learn a whole lot about enclosures and mechanical design generally. >> Turns out that you have to put an air vent on the enclosure to prevent >> pumping water inside due to atmospheric pressure differences. That >> leads to working of the O-ring seals, which wears them out. >> >> We considered using a bellows, but atmospheric pressure varies +-7% or >> so, which makes for a pretty big, floppy bellows. Hermetic construction >> is possible but very expensive, and relies on glass or ceramic insulated >> connectors. The glass would have had to be brazed or indium-soldered to >> the lid, which leads to CTE mismatch problems. > > A balloon inside?Doesn't help--you need something to reduce the pressure drop across the seals. An aluminized rubber diaphragm inside the box, with one side vented, might work. I made a calculation that 50 grams of 5A molecular sieve would keep the inside dry for about 10 years. The board has a T/H sensor on it, so it can complain if the sieve gets saturated. We're conformal-coating the boards, and the sensors are running at zero bias. Doing the latter is unusual for me, but the bandwidth only needs to be 200 Hz or so. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●April 6, 20202020-04-06
While not a component... Early in my career, it was demonstrated to me that you could make a reasonably accurate RF millivoltmeter out of an analog Simpson 260 voltmeter. (Without modifying it, of course.)
Reply by ●April 6, 20202020-04-06
On 6/4/20 5:04 am, George Herold wrote:> On Saturday, April 4, 2020 at 8:49:22 PM UTC-4, pcdh...@gmail.com wrote: >> Following up on blocher's sterling work,(*) >> >> Many of us use parts off-label, often very successfully. A few examples: >> >> SAV-551+ pHEMTs make very good wideband bootstraps. Their f_max is around 12 GHz, but they're amazingly stable. >> >> 74HC4352s make good flying-capacitor diff amp front ends. >> >> TMUX1511s make very nice analogue lock-ins--their Coff*Ron FOM is almost in a class with relays, but 1E5 times faster. >> >> Zero-ohm jumpers have about the right resistance to stabilize LDO regulators with ceramic output caps. (It's good to be able to disconnect the supplies during bring-up, and putting the jumper between the reg and the output cap has this additional benefit. >> >> Your faves? > Wow nice list! > I'd like to take a 'part' off the alt. use list. > I use to tout the use of 20 zeners rev biased at ~10-100 uA > as audio noise sources. When I went to replace the pack I had > it turned out I had a 'golden string'. I had to order a bunch > from different suppliers to find noisy batch. (And that still wasn't as > good(noisy) as the original... but it's obvious that almost no one wants > a noisy zener.)George, I'm trying to understand this. What do you need 20 zeners for? FWIW, I'm currently making a broadband noise source for testing filters up to 1.5GHz. Still scratching around for the best source to put before a string of ERA-3 MMIC amplifiers. The BFR93A data sheet says abs max Vbe is 2V, but it doesn't zener at 5V. Although avalanche zeners produce much more noise, I'd rather not boost my 5V supply (though I might need to). I wonder how much reverse current a microwave Shottky diodes (say HSMS-286) would survive. Abs max peak reverse voltage is 4V, so it might withstand 5V anyway... Any better suggestions for a device I might have in the drawer already? Clifford Heath.
Reply by ●April 6, 20202020-04-06
On Mon, 6 Apr 2020 17:43:46 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 2020-04-05 13:39, jlarkin@highlandsniptechnology.com wrote: >> On Sun, 5 Apr 2020 12:17:03 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 2020-04-05 11:42, jlarkin@highlandsniptechnology.com wrote: >>>> On Sun, 5 Apr 2020 10:52:29 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 2020-04-05 00:09, jlarkin@highlandsniptechnology.com wrote: >>>>>> On Sat, 4 Apr 2020 17:49:18 -0700 (PDT), pcdhobbs@gmail.com wrote: >>>>>> >>>>>>> Following up on blocher's sterling work,(*) >>>>>>> >>>>>>> Many of us use parts off-label, often very successfully. A few >>>>>>> examples: >>>>>>> >>>>>>> SAV-551+ pHEMTs make very good wideband bootstraps. Their f_max is >>>>>>> around 12 GHz, but they're amazingly stable. >>>>>> >>>>>> They make excellent switches too. Rds-on is never specified for RF >>>>>> parts, but it's about 2 ohms for the 551. >>>>>> >>>>>>> >>>>>>> 74HC4352s make good flying-capacitor diff amp front ends. >>>>>>> >>>>>>> TMUX1511s make very nice analogue lock-ins--their Coff*Ron FOM is >>>>>>> almost in a class with relays, but 1E5 times faster. >>>>>>> >>>>>>> Zero-ohm jumpers have about the right resistance to stabilize LDO >>>>>>> regulators with ceramic output caps. (It's good to be able to >>>>>>> disconnect the supplies during bring-up, and putting the jumper >>>>>>> between the reg and the output cap has this additional benefit. >>>>>>> >>>>>>> Your faves? >>>>>> >>>>>> Some digital bus and USB switches are cheap and are excellent, >>>>>> super-fast analog multiplexers. >>>>>> >>>>>> Some chips are useful just for their ESD diodes. >>>>>> >>>>>> LVDS line receivers are super-fast, dirt cheap RRIO comparators. >>>>> >>>>> I've used them like that at your suggestion. Snazzy if you don't need >>>>> super low offset voltage. (And if you do, every comparator slows way down.) >>>>> >>>>>> >>>>>> An LED can be used as the voltage reference for an NPN current >>>>>> source. The tempcos can be made to almost cancel. >>>>>> >>>>>> High value AlN resistors can be used as thermal bridges. >>>>> >>>>> That's interesting. I recall discussing some very expensive parts sold >>>>> specifically for DC isolating thermal pours. >>>>> >>>>>> >>>>>> Surface-mount platinum RTDs can be used in experiments, as both >>>>>> heater and sensor, to quantify resistor heat sinking and thermal >>>>>> transients. >>>>>> >>>>>> Surface-mount resistors can be last-resort fuses. >>>>>> >>>>>> Low-barrier schottky diodes can be used in reverse as >>>>>> constant-current things. Tempcos are not great. The same diode can >>>>>> charge and discharge a capacitor. >>>>> >>>>> Interesting. Are they reasonably repeatable unit-to-unit? >>>> >>>> For modest values of reasonable. It's Is, which is huge for >>>> schottkies, hundred nA sorts of numbers. I've posted my RF detector >>>> which is a diode and a capacitor. It's in production. >>>> >>>>> >>>>>> >>>>>> Some self-protecting SSRs can be used as electronic fuses. As can a >>>>>> 3t regulator with the adj pin open. >>>>>> >>>>>> Depletion fets are nice capacitor bleeders. Ditto 3t reg as a >>>>>> current sink. >>>>> >>>>> >>>>>> >>>>>> A bit of open-load transmission line can be a high-frequency peaker. >>>>>> I have that option in my GHz o/e layout. >>>>> >>>>> Interesting. How does that work? Normally I think of O/C tlines as a >>>>> series resonance to ground. >>>> >>>> Stick a drooling-rise step into one end of a transmission line and it >>>> will overshoot and snap up the waveform at the other end. Adjust the >>>> source impedance, or terminate a little, to trim the step response. >>>> It's sharper than RC peaking, so compensates things like Ft rolloff or >>>> skin effect. >>> >>> Okay, so not really open-circuited. I'll try it out. That could >>> potentially have helped that single-diode sampler gizmo--its speed was >>> limited by the rise time of the line receiver driving the pHEMT switch. >>> That one used a capacitor plus a short, mismatched shunt stub to make >>> the sampling pulse from a falling edge. >> >> The soft peaking helps when a step has a soft corner on the rise, >> which is very common. That's why people who do fast stuff cheat and >> measure risetime 20/80. >> >>> >>>> >>>> I had a profound, life-changing revelation recently. If you don't poke >>>> a fast rise into a passive transmission line, you won't get a fast >>>> reflection. I wasted all those years designing absorptive lowpass >>>> filters. >>> >>> Gasp! ;) >>> >>>> >>>>> >>>>> >>>>>> >>>>>> Someone said never use an opamp as a comparator. They were wrong. >>>>> >>>>> Gotta watch for the antiparallel diodes on the inputs, though. For slow >>>>> stuff, LM358s work great as comparators--the inputs survive going way >>>>> above the supply. >>>>> >>>>>> >>>>>> An rro opamp can also be used as a current limiter/fuse. >>>>>> >>>>>> You can do all sorts of things with ribbon cable. >>>>>> >>>>>> Some HV diodes and the c-b junctions of some transistors make >>>>>> awesome drift step-recovery (Grehkov) diodes. >>>>>> >>>>>> BFT25s can be used as fA-leakage diodes. >>>>>> >>>>>> Dual-winding inductors, like DRQ127, can do all kinds of tricks. >>>>> >>>>> Annoying that they don't tell you k in the datasheet, and you can't even >>>>> back it out from the series-connected inductance, which is quoted as >>>>> exactly four times the parallel-connected value. >>>> >>>> The k's are really high. Easy to measure. >>> >>> That's unusual for a 'coupled inductor'. I normally expect it to be >>> around 0.85. >> >> The DRQs are bifilar. Two or three 9's. >> >> And a lot of capacitance. They make nice autotransformer flybacks. >> Does that have a better name? >> >> >> >>>>>> A toroidal inductor can be a liquid level sensor. >>>>> >>>>> That one I haven't heard about. Are you looking for the NMR signal? ;) >>>> >>>> A conductive liquid is a shorted turn. >>> >>> At sufficiently low frequency, anyway. >>> >>> We've started putting little Sensirion T/H sensors in a lot of things. >>> When using TECs, it's awfully nice to be able to compute the dew point, >>> for instance, and in outdoor applications (e.g. our fire sensors for >>> harvesters) it's good to be able to predict when the window is liable to >>> fog up on the inside. >>> >>> We use IP67+ enclosures with bags of 5A molecular sieve inside, which is >>> super cheap and will absorb 50% of its own mass in water. Simon has had >>> to learn a whole lot about enclosures and mechanical design generally. >>> Turns out that you have to put an air vent on the enclosure to prevent >>> pumping water inside due to atmospheric pressure differences. That >>> leads to working of the O-ring seals, which wears them out. >>> >>> We considered using a bellows, but atmospheric pressure varies +-7% or >>> so, which makes for a pretty big, floppy bellows. Hermetic construction >>> is possible but very expensive, and relies on glass or ceramic insulated >>> connectors. The glass would have had to be brazed or indium-soldered to >>> the lid, which leads to CTE mismatch problems. >> >> A balloon inside? > >Doesn't help--you need something to reduce the pressure drop across the >seals. An aluminized rubber diaphragm inside the box, with one side >vented, might work.I meant that it would be vented to the outside. Little plastic tube or something.> >I made a calculation that 50 grams of 5A molecular sieve would keep the >inside dry for about 10 years. > >The board has a T/H sensor on it, so it can complain if the sieve gets >saturated. > >We're conformal-coating the boards, and the sensors are running at zero >bias. Doing the latter is unusual for me, but the bandwidth only needs >to be 200 Hz or so.I guess the seive would soak up humidity and reduce the pressure inside, so a tiny flow through the seals would introduce a little more humidity. Wouldn't that eventually get to zero humidity and zero pressure differential? I guess atmospheric changes would still pump the system slightly. Mothballs?> >Cheers > >Phil Hobbs-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●April 6, 20202020-04-06
On Mon, 6 Apr 2020 14:50:46 -0700 (PDT), mpm <mpmillard@aol.com> wrote:>While not a component... > >Early in my career, it was demonstrated to me that you could make a reasonably accurate RF millivoltmeter out of an analog Simpson 260 voltmeter. > >(Without modifying it, of course.)Mo found this at some neighborhood junk sale and bought it for me. $3 or something. https://www.dropbox.com/s/tz0panr4f1nlqer/RF_Ammeter.JPG?raw=1 It's probably a thermocouple. How did that Simpson thing work? I have some Spice models of an RF detector using an SMS7621 low-barrier schottly. It works around 50 mV RMS. -- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
Reply by ●April 6, 20202020-04-06
On 2020-04-06 21:35, jlarkin@highlandsniptechnology.com wrote:> On Mon, 6 Apr 2020 17:43:46 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 2020-04-05 13:39, jlarkin@highlandsniptechnology.com wrote: >>> On Sun, 5 Apr 2020 12:17:03 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 2020-04-05 11:42, jlarkin@highlandsniptechnology.com wrote: >>>>> On Sun, 5 Apr 2020 10:52:29 -0400, Phil Hobbs >>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>>> >>>>>> On 2020-04-05 00:09, jlarkin@highlandsniptechnology.com wrote: >>>>>>> On Sat, 4 Apr 2020 17:49:18 -0700 (PDT), pcdhobbs@gmail.com wrote: >>>>>>> >>>>>>>> Following up on blocher's sterling work,(*) >>>>>>>> >>>>>>>> Many of us use parts off-label, often very successfully. A few >>>>>>>> examples: >>>>>>>> >>>>>>>> SAV-551+ pHEMTs make very good wideband bootstraps. Their f_max is >>>>>>>> around 12 GHz, but they're amazingly stable. >>>>>>> >>>>>>> They make excellent switches too. Rds-on is never specified for RF >>>>>>> parts, but it's about 2 ohms for the 551. >>>>>>> >>>>>>>> >>>>>>>> 74HC4352s make good flying-capacitor diff amp front ends. >>>>>>>> >>>>>>>> TMUX1511s make very nice analogue lock-ins--their Coff*Ron FOM is >>>>>>>> almost in a class with relays, but 1E5 times faster. >>>>>>>> >>>>>>>> Zero-ohm jumpers have about the right resistance to stabilize LDO >>>>>>>> regulators with ceramic output caps. (It's good to be able to >>>>>>>> disconnect the supplies during bring-up, and putting the jumper >>>>>>>> between the reg and the output cap has this additional benefit. >>>>>>>> >>>>>>>> Your faves? >>>>>>> >>>>>>> Some digital bus and USB switches are cheap and are excellent, >>>>>>> super-fast analog multiplexers. >>>>>>> >>>>>>> Some chips are useful just for their ESD diodes. >>>>>>> >>>>>>> LVDS line receivers are super-fast, dirt cheap RRIO comparators. >>>>>> >>>>>> I've used them like that at your suggestion. Snazzy if you don't need >>>>>> super low offset voltage. (And if you do, every comparator slows way down.) >>>>>> >>>>>>> >>>>>>> An LED can be used as the voltage reference for an NPN current >>>>>>> source. The tempcos can be made to almost cancel. >>>>>>> >>>>>>> High value AlN resistors can be used as thermal bridges. >>>>>> >>>>>> That's interesting. I recall discussing some very expensive parts sold >>>>>> specifically for DC isolating thermal pours. >>>>>> >>>>>>> >>>>>>> Surface-mount platinum RTDs can be used in experiments, as both >>>>>>> heater and sensor, to quantify resistor heat sinking and thermal >>>>>>> transients. >>>>>>> >>>>>>> Surface-mount resistors can be last-resort fuses. >>>>>>> >>>>>>> Low-barrier schottky diodes can be used in reverse as >>>>>>> constant-current things. Tempcos are not great. The same diode can >>>>>>> charge and discharge a capacitor. >>>>>> >>>>>> Interesting. Are they reasonably repeatable unit-to-unit? >>>>> >>>>> For modest values of reasonable. It's Is, which is huge for >>>>> schottkies, hundred nA sorts of numbers. I've posted my RF detector >>>>> which is a diode and a capacitor. It's in production. >>>>> >>>>>> >>>>>>> >>>>>>> Some self-protecting SSRs can be used as electronic fuses. As can a >>>>>>> 3t regulator with the adj pin open. >>>>>>> >>>>>>> Depletion fets are nice capacitor bleeders. Ditto 3t reg as a >>>>>>> current sink. >>>>>> >>>>>> >>>>>>> >>>>>>> A bit of open-load transmission line can be a high-frequency peaker. >>>>>>> I have that option in my GHz o/e layout. >>>>>> >>>>>> Interesting. How does that work? Normally I think of O/C tlines as a >>>>>> series resonance to ground. >>>>> >>>>> Stick a drooling-rise step into one end of a transmission line and it >>>>> will overshoot and snap up the waveform at the other end. Adjust the >>>>> source impedance, or terminate a little, to trim the step response. >>>>> It's sharper than RC peaking, so compensates things like Ft rolloff or >>>>> skin effect. >>>> >>>> Okay, so not really open-circuited. I'll try it out. That could >>>> potentially have helped that single-diode sampler gizmo--its speed was >>>> limited by the rise time of the line receiver driving the pHEMT switch. >>>> That one used a capacitor plus a short, mismatched shunt stub to make >>>> the sampling pulse from a falling edge. >>> >>> The soft peaking helps when a step has a soft corner on the rise, >>> which is very common. That's why people who do fast stuff cheat and >>> measure risetime 20/80. >>> >>>> >>>>> >>>>> I had a profound, life-changing revelation recently. If you don't poke >>>>> a fast rise into a passive transmission line, you won't get a fast >>>>> reflection. I wasted all those years designing absorptive lowpass >>>>> filters. >>>> >>>> Gasp! ;) >>>> >>>>> >>>>>> >>>>>> >>>>>>> >>>>>>> Someone said never use an opamp as a comparator. They were wrong. >>>>>> >>>>>> Gotta watch for the antiparallel diodes on the inputs, though. For slow >>>>>> stuff, LM358s work great as comparators--the inputs survive going way >>>>>> above the supply. >>>>>> >>>>>>> >>>>>>> An rro opamp can also be used as a current limiter/fuse. >>>>>>> >>>>>>> You can do all sorts of things with ribbon cable. >>>>>>> >>>>>>> Some HV diodes and the c-b junctions of some transistors make >>>>>>> awesome drift step-recovery (Grehkov) diodes. >>>>>>> >>>>>>> BFT25s can be used as fA-leakage diodes. >>>>>>> >>>>>>> Dual-winding inductors, like DRQ127, can do all kinds of tricks. >>>>>> >>>>>> Annoying that they don't tell you k in the datasheet, and you can't even >>>>>> back it out from the series-connected inductance, which is quoted as >>>>>> exactly four times the parallel-connected value. >>>>> >>>>> The k's are really high. Easy to measure. >>>> >>>> That's unusual for a 'coupled inductor'. I normally expect it to be >>>> around 0.85. >>> >>> The DRQs are bifilar. Two or three 9's. >>> >>> And a lot of capacitance. They make nice autotransformer flybacks. >>> Does that have a better name? >>> >>> >>> >>>>>>> A toroidal inductor can be a liquid level sensor. >>>>>> >>>>>> That one I haven't heard about. Are you looking for the NMR signal? ;) >>>>> >>>>> A conductive liquid is a shorted turn. >>>> >>>> At sufficiently low frequency, anyway. >>>> >>>> We've started putting little Sensirion T/H sensors in a lot of things. >>>> When using TECs, it's awfully nice to be able to compute the dew point, >>>> for instance, and in outdoor applications (e.g. our fire sensors for >>>> harvesters) it's good to be able to predict when the window is liable to >>>> fog up on the inside. >>>> >>>> We use IP67+ enclosures with bags of 5A molecular sieve inside, which is >>>> super cheap and will absorb 50% of its own mass in water. Simon has had >>>> to learn a whole lot about enclosures and mechanical design generally. >>>> Turns out that you have to put an air vent on the enclosure to prevent >>>> pumping water inside due to atmospheric pressure differences. That >>>> leads to working of the O-ring seals, which wears them out. >>>> >>>> We considered using a bellows, but atmospheric pressure varies +-7% or >>>> so, which makes for a pretty big, floppy bellows. Hermetic construction >>>> is possible but very expensive, and relies on glass or ceramic insulated >>>> connectors. The glass would have had to be brazed or indium-soldered to >>>> the lid, which leads to CTE mismatch problems. >>> >>> A balloon inside? >> >> Doesn't help--you need something to reduce the pressure drop across the >> seals. An aluminized rubber diaphragm inside the box, with one side >> vented, might work. > > I meant that it would be vented to the outside. Little plastic tube or > something. > > >> >> I made a calculation that 50 grams of 5A molecular sieve would keep the >> inside dry for about 10 years. >> >> The board has a T/H sensor on it, so it can complain if the sieve gets >> saturated. >> >> We're conformal-coating the boards, and the sensors are running at zero >> bias. Doing the latter is unusual for me, but the bandwidth only needs >> to be 200 Hz or so. > > > > I guess the seive would soak up humidity and reduce the pressure > inside, so a tiny flow through the seals would introduce a little more > humidity. Wouldn't that eventually get to zero humidity and zero > pressure differential? > > I guess atmospheric changes would still pump the system slightly.If we start with a dry atmosphere inside, humidity by itself would not be a first-order forcing function. Air pressure varies +- 7% or thereabouts on time scales of a few days. If you assume that the variations are the same inside the box, you can calculate how much water will get in. Our stuff has to work in medium-extreme conditions. Harvesters are still working in January in some places--I've spent a little January time in West Texas installing and verifying installations, at temperatures well below freezing and with high winds. Simon has done about three times more of that stuff. It's difficult. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●April 7, 20202020-04-07
On Monday, April 6, 2020 at 9:43:33 PM UTC-4, jla...@highlandsniptechnology.com wrote:> On Mon, 6 Apr 2020 14:50:46 -0700 (PDT), mpm wrote: > > >While not a component... > > > >Early in my career, it was demonstrated to me that you could make a reasonably accurate RF millivoltmeter out of an analog Simpson 260 voltmeter. > > > >(Without modifying it, of course.) > > Mo found this at some neighborhood junk sale and bought it for me. $3 > or something. > > https://www.dropbox.com/s/tz0panr4f1nlqer/RF_Ammeter.JPG?raw=1> > It's probably a Thermocouple.Yes, they are Thermocouple meters. Those were used to measure the current to an antenna. Larger ones were used in Broadcasting to log transmitter output in the station's daily engineering logs for the FCC.> How did that Simpson thing work? > > I have some Spice models of an RF detector using an SMS7621 > low-barrier Schottly. It works around 50 mV RMS.Simple RF probes. There are a lot of minor variations. I have a Fluke85RF. The link is for a two page manual, and schematic. It used a Germanium diode, but modern diodes are usable. and have a better frequency response. The ARRL handbook has had a probe design in every issue that I've ever seen. The early ones used a dual diode tube like a 6AL5. If you need better accuarcy at low levels, an old Boonton 92 series is hard to beat. Its sucessor, the 9200 is even better. It is digital and it has IEEE-488 interface as an option. Probes often cost more than the meters, and the cables are as well, but you can find them on Ebay. I've ought 'untested' 92 meters with a probe and cable cheap, because the seller is clueless. I will be building clones of some of their probes, now that I have a lathe. and suitable shielded cable. Wirepro still makes the origin Amphenol two pin microphone connectors, and I have a new, 250 foot spool of the cable. <https://www.schematicsunlimited.com/f/fluke/fluke-85rf>
