Demo ideas

On a sunny day (Sat, 9 Feb 2019 13:28:27 -0500) it happened Phil Hobbs wrote in :

Use your sensor or whatever it is to change the VCO input of a 4046 that runs in the audio range? Offset voltage from sensor subtracted by opamp, some gain,

Or digtal output from sensor to Linux PC running sgen, any math you line in between.

Or sensor voltage -> PIC ADC -> any math you like in asm -> PIC PWM -> audio amp.. or PIC PWM into small speaker:

Or NTC in 1 MHz oscillator, beat against medium wave broadcast station :-)

Well the list of ways to do that is endless...

What supports the isolated object?

I guess the oscillator could be battery powered and output its signal magnetically or optically. Otherwise there would have to be lead wires which would conduct heat. Or just suspend an LC tank that has a very bad capacitor. I have some N4700s, but you can do much worse.

Hey, you're an optics guy: do something optical! Interference fringes maybe.

Send us a link to the patent application after it's filed. Sounds interesting.

I'm expecting it to be battery powered and just sit there on a table. The thermal conduction isn't a serious limitation as long as there's enough power available.

I'm thinking about just using a ceramic cell phone speaker. Doesn't have to be too loud. Making it super temperature sensitive would be good--like some audible shift when you pass your hand over it without touching.

That's an interesting idea, but it would have to be self-contained. Stabilized lasers, PCR reactors, sensors for road icing, and stuff like that are among the potential applications.

Yeah, it's pretty fun. I'll show you the demo sometime. (It has an analogue square-rooter in the loop.)

Cheers

Phil Hobbs

For a demo, I was thinking about parallel mirrors at the ends of a little tube made out of something with a terrible expansion tempco, plastic even. Shine a laser at it and change the temp and watch the fringes squirm. Make a movie.

That might be too intellectual for some of your prospects.

I'm busy Spicing a new pin driver; that circuit is sort of my lifetime hobby. Just when I had a wonderful circuit, two critical parts (RF PNP and big PHEMT) went EOL.

I've made servos with square-root functions included. In one case I was servoing both a supply voltage and a PWM signal, that made the result go by the square of the servo output, so I added a square-root. It worked very well, over three decades of linear output range. (I didn't try removing the square root, to see how badly it'd do.) BTW, analog multiplier ICs, to make the square root, are pretty scarce, and none work at the low voltages we like to use now.

Yah, I know. Broadcom and NXP have a lot to answer for.

Fortunately Mini-Circuits is trying to help, and Infineon still makes fast PNP arrays.

Cheers

Phil Hobbs

This one uses a power device, a dual BJT and a few resistors. In the SPICE spherical-cow universe, it's +-5% of a real square root in the region of interest.

As long as the BJTs are at reasonably similar temperatures, the errors are mainly offsets, so the overall FB loop can compensate.

Cheers

Phil Hobbs

On Feb 9, 2019, Phil Hobbs wrote (in article ):

Sounds ideal for controlling the temperature of the crystal in a reference oscillator. Such things are offered commercially, called an oven controlled crystal oscillator (OCXO). ppb frequency stability is obtainable.

The theory of such ovens was laid out by Richard Karlquist of HP, back in the day.

"THE THEORY OF ZERO-GRADIENT CRYSTAL OVENS", Richard Karlquist et al, and Cutler, Karlquist, et. al, "High Thermal Gain Oven with Reduced Probability of Temperature Gradient Formation for the Operation of a Thermally Stable Oscillator," U. S. Patent 5,729,181.

Joe Gwinn

Huh, well my first thought for thermal control was a diode laser. As for a demo maybe an unequal arm Michelson, as the wavelength changes you can watch the nice fringe pattern change.

Then lock your gizmo in and it stops changing... (except for the thermal expansion of the optic table holding the interferometer.)

George H.

I've moved on with my life, to GaN and SiC. I wonder how long they will last.

The Thaler THAT 2181 is a possible alternative to the Analog Devices AD734, and could be used at lower supply voltages - down to +/-4V

It's not touted as a multiplier but does seem to depend on a Gilbert cell.

There's a second source for them now via "CoolAudio" electronics in China, $3 each in small quantity:

Yeah needs to be more dramatic.

Put some kind of thermally-activated triggering device in the volume that fires a huge volume of pink glitter and fart-scent spray around the conference room if it hits a certain temperature and put the whole apparatus on a hot plate with a dramatic RED 7-segment display like the show "24" showing the temperature rising to the critical temperature.

The attendees have to agree to sign off on a purchase order if their activating your device saves the day/their suits. Tell them it's a really nasty-smelling fart-spray, too, the worst there is. Lock the doors.

There are likely ways to tone this idea down a bit if fear of being arrested and/or deported but something in that vein would be good. Just brain-storming here.

If 'twere me, I'd say keep it simple: a hair dryer and a CO2 jet will make hot and cold winds, and a thermistor (with a bridge to null and amplifier to gain-control) can be made to swing a thermometer needle impressively.

Just apply heat for a second and watch the needle move. Then apply cold. Power the regulator and repeat. It'd be best if the regulator activation was graphically illustrated (big neon sign saying 'THERMOSTAT ENGAGED' would be nice).

Extra points for blue and red blower activator buttons, for icewater-based coldside option, where everyone can see the ice.

Most people are visual rather than auditory, so the suggestions using a v isual display are good (the digital "24" display is a bit over the top, may be).

You can play to your audience- what are they interested in protecting? If electronics, one of their products would be good with whatever display or readout or other indication of out-of-range failure is appropriate. Keep th e circuitry as obvious and transparent as possible to eliminate suspicions of fakery of course.

Speaking of that you could demonstrate on something pretty much anyone ca n look at and recognize, something not electronics-related.

You could go with protecting raw egg white from denaturing if you can get past the obvious spoilage and potential health risks of such a demonstrati on (in other words have someplace to dispose of the unprotected mess), but cracking and egg and separating out the whites while delivering your spiel is a great convincer of geniuneness.

If you do that they will naturally ask about the potential range of opera tion- what is that range, anyway? Can you use gallium alloys or other "exot ic" materials to demonstrate the high/low ends without suspicion of fakery either accidental of intentional?

I mention fakery not because I suspect you, but because something like yo ur idea will be a hard sell and people not intimately familiar with the kin d of electronic stuff we are will see it as "magic" and need some more basi c convincing.

Mark L. Fergerson

How about a tiny battery-powered device with LEDs that change color dramatically over a small temp range? That would be fun.

Sort of AC couple it.

Oh c'mon can't we have a stink-bomb demo pleeeaseee...