an electronish puzzle

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

So do I, with certain reservations.

What seems to have gotten lost here is pretty simple, so I will state it more succintly:

1. "The" theory says that the 1st order effect is 0, no change in observed collector current.

1. There are 2nd order effects. They are hard to quantify, (especially for people like us who do not live and breath that sort of stuff).

2. You have observed a very small change in collector current, linear to some degree, when performing the experiment with a real part.

Do you see, in that set of statements, any collision between "theory" and your parts?

Ok. But the right experts can avoid the need for some experiments and inform the design of others.

I read in sci.electronics.design that Larry Brasfield wrote (in ) about 'an electronish puzzle', on Mon, 21 Mar 2005:

Back in the good old days, the *standard* low-value ceramic caps were of N750 material. That, in due course, brought the matter of component TCs to the attention of every newbie.

"Pain in the arse" is a good assessment. The current product uses a varicap driven by an LM45 temp sensor, a couple of opamps, and a trimpot. Even without soldering, adjusting the tc is a huge, tedious nuisance. Now I want to make a really tiny version, so an NTC cap would be ideal. There's a huge matrix of possibilities combining fixed caps and NTCs; NTCs are theoretically available from N220 to N5600. Disc NTC caps are still somewhat available, but it's hard to get surface-mounts unless you want to buy a million, which makes experimenting problematical.

If I could get the TC down from -125 to, say, +-40 maybe, it would solve my problem.

John

I plan to do just that, presuming you mean variations on the experiment reported by John Larkin. AC b-e current is sure to separate thermal effects from the other effects.

The "ideal", in his case, is to prove other people stupid in cases where ordinary insults and obscenities aren't enough.

If Fred had a legitimate need, or just intellectual curiosity, about this issue, then that has my respect; so why doesn't he share it with us?

If he did it to prove that someone is an idiot, then he's running true to form.

The "oscilloscope simulators" part doesn't sound familiar to me.

Can't recall that. Got a reference?

Oh, do you mean the cap on the Xilinx pin? That's hardly an oscilloscope simulator! It's zapping some ringing or something. You might note that I shared that observation with the OP in the hopes of helping him with a similar problem, and did *not* insult him or call him an idiot.

Theory is only useful if it's predictive; even the scientists agree on that. I just finished reading Dahl's book, "Flash of the Cathode Rays", which is all about this. Surprisingly good, fun to read book, given that it's about the history of subatomic particles. The parts about N-rays and sub-e charges are especially cool.

I chastise Fred for heaping extended, crude, obscene, and frequent insults on the majority of the posters in this group, including newbies who ask innocent (if often naive) questions. He's not here to learn, or to help, or to have fun, but mostly just to show how smart he is and how stupid everybody else is. I wonder what the real story is of Fred's life; he's silent on that.

For pete's sake, read his posts. He's rude, obscene, and perfectly mean-spirited. If that's the sort of person you admire, well...

John

Because this is a discussion group, not a scientific journal. And besides, somebody who knows a lot about this may have ideas that could help me.

John

The inductor I'm using in this oscillator, a 1008 surface-mount, has (apparently) a strong positive TC. All the aircore inductors I've used had positive TCs; I guess they just expand with temperature, and bigger diameter makes more L. This is only 150 nH, so a temperature-compensating core is probably out of the question.

John

Years ago I designed a scheme that tested an oven-less crystal oscillator over several days.

A DAC was used to adjust the varicap voltage to bring the oscillator frequency dead-on.

Data was stored in a ROM that was addressed dependent on temperature.

Oven performance without oven.

...Jim Thompson

--- Fred Bloggs wrote:

In the case of the OP292 thread, the motivation was to make a dead certain diagnosis of the Nazi Clarence and his problem- and that is what I did- also ordered some OP292's and played around with it some more. ....

John Lark You actually ordered parts and built circuits to prove somebody from a newsgroup to be wrong? That's pushing the top range of the getalifeometer!

....

If you believe what you quoted:, "One experiment is worth a thousand expert opinions.", then buying or building parts to prove a point in the real world isn't something which should be ridiculed, it's something which should be respected. After all, spending discretionary income just to prove a point with no hope of remuneration or, God forbid, gain, rocks. That is, it proves committment to an ideal.

I seem to recall that you said that as a result of experimentation on some of your stuff you're now shipping equipment with "oscilloscope simulators" installed which, without, equipment you're selling won't work properly. You also said that you didn't understand just why it made the equipment work, so that seems to me to be a good example of experiment taking the place of theory.

Anyway, it seems to me that you're unfairly chastising Fred for going for empirical evidence of success since you're doing the same thing and, eventually, it all has to work here, in the real world.

-- John Fields

Well, you are implying that I can't tell a straight line from an exponential. That's not very nice, you know.

John

Right; I think that's how a lot of tcxo's are done nowadays; much nicer than selecting resistors in thermistor networks. The second-order problem with tcxo's of any kind is slow phase noise resulting from the differing thermal time constants of the sensor network and the crystal itself. Only a massive oven can fix that.

There were a few barbarians who selectively digitally *dropped cycles* as a function of temperature! May they rot in Hell.

Our alternative is to measure temp with an LM75 (spi) sensor, crunch the numbers (we have a uP on board) and drive a sot-23 serial dac and a varicap to tweak the tc. The kiddies are advocating for that. I'd like to plop a single 0603 NTC cap on the board to do the same thing, because I'm old-fashioned and also because I have to pay for the parts a few thousand times over. Besides, I'm probably the guy who'd wind up writing the code.

John

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

I was not trying to say that. I'm sure there is a thermal effect, and I intend to see the others (such as you appear to have reported) without the confusion of a superimposed exponential.

"John Larkin" a écrit dans le message de news: snipped-for-privacy@4ax.com...

Maybe you can buy a tin of violet paint?

OK, but you're going to have to resolve nanoamps in milliseconds. Sounds like a project.

John

Oh, right. These things do get tangled sometimes.

John

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Yes. I have a long-record, digitizing o'scope, so I thought to take advantage of the narrowband nature of the expectable response to make that tractable by processing records that are many cycles long. Some external gain is likely needed, but that is not much different from photocurrent amplifiers I have worked on at similar levels and frequencies. Given the signal levels you report, it looks simple enough to do just for fun.

I read in sci.electronics.design that Fred Bartoli wrote (in ) about 'an electronish puzzle', on Tue, 22 Mar 2005:

Violet is N750. OK, making 1/3 of the capacitance N750 and the rest NP0/COG would do. But yellow paint gets you N220. (;-)