LC_Tuning-Outside_the_Box

Button batteries are a bad idea, IMO. AA or LiIon, please.

The distortion is good but unnecessary. I'm looking for a set of bluetooth around-the-ear[*] headsets (no mic needed) for a reasonable price. Bluetooth is a requirement, since that's that MP3 players, cell phones, and laptops have. Can't find them. We don't need yet another standard.

Just for you, we'll use AA and you'll get much longer time-of-use. Just one thing. Do you have at least one large, husky ear to hang the device on? The button battery works for most people and doesn't seem to 'tear' their ear off, since inserted into the ear opening itself.

On Sat, 23 Nov 2013 08:20:12 -0800 (PST), Greegor Gave us:

Wouldn't that be a Philbrookabuster?

On Sat, 23 Nov 2013 11:29:46 -0500, snipped-for-privacy@attt.bizz Gave us:

Consumption should be down low enough to use a supercap and simply recharge it more often. But look at the longevity gain over limited life cells. If such a cap can be made in an appropriate form factor for the task. Make it inductive recharge and we could use proximity re-fueling and reduce needs for hard charging station rest/charge period requisites.

I just broke a lens. A pie-piece shaped quarter of the lens broke off. The point left on each piece was more than sharp enough to slice an eyeball. Don't believe the "safety" propaganda. The optician said "that can't happen". Well...

I guess I don't see the math behind it, particularly with a lens in the equation (been too long since college optics - blech!),

But you're getting two imperfect images, right? A null that's not zero is sometimes difficult to measure. An optometrist will correct both at the same time, then fiddle with both until the best null can be found.

Sure. That was JL's point about them being in control vs. you.

You still need their Rx to order glasses in most places.

Zenni wants an Rx, but you can lie in most jurisdictions.

Seems reasonable. The tools aren't set up for that but it shouldn't be all that difficult to do. Perhaps they'd be out of a job, then.

What? They never used to. You just put in the specs for your specs. I just bought a few different pairs to try out.

Cheers

Phil Hobbs

surprised me too, here I've bought glasses online here and you just put in the numbers, when I tried an American website they required a prescription or details to get it from the optometrist

-Lasse

I just type in the numbers... haven't seen any reference to a prescription. I can make up my own formulas and try them.

Yes. There's hundreds of years of tradition and turf in the eyeglass business, and a lot of ass-covering. For example, optimetrists obviously know your inter-pupillary distance but usually refuse outright to tell you. The internet is breaking that up.

"Inserted into the ear opening" doesn't sound like "around the ear". ;-)

The point is that 40hrs isn't enough and batteries get expensive. Add to that a nonstandard RF scheme and you have a non-starter.

They've always asked me for the Rx and the date, which I fudge. I get a checkup once a year, now, but usually only half the prescriptions I use (to pairs of glasses - normal and computer-use).

I have to have bifocals and progressives are much better than "lined". They're not all that cheap, though much less than the optician's.

IIRC, Zenni explains the differences.

Here's half of the full H-bridge amplifiers that I built for my 1977

I pulled out the stock AM/FM radio, replaced it with a nice Panasonic tuner and built full H's for each side, front and rear... probably why my hearing is so bad now... Rossini's "La gazza ladra" (my favorite of his overtures), and a lot Dixieland, at full power ;-)

Wonder if anyone can decipher the gimmicks in this amplifier? ...Jim Thompson

On Sunday, 24 November 2013 01:19:39 UTC+11, Maynard A. Philbrook Jr. wrot e:

gative resistor circuit onto a LC and let it self oscillate. This would be instead of sweeping it.

simply turn this into a VCO... but I haven't gotten that far yet.

the 17th November 2013 at 05:06:39 and 05:47:53 UTC+11, in the original "T uning an LC" thread.

mulation, but not yet in real life, because I haven't get soldered the bits together). It needs a 90 degree phase shift network (which Jim doesn't see m to have noticed yet) and a high-output-impedance - current source - drive to push the artificial reactive current into the tank circuit where it loo ks like either a parallel inductance or a parallel capacitance, either posi tive or negative depending on your point of view and the sign of gain.

t to obtain oscillator for decades, what makes your so special?

That aspect of it isn't particularly special. What I am doing is using an L C tank circuit to set the nominal oscillation frequency, a NatSemi/TI LME49

I was bit surprised that I could shift the frequency up or down by a factor of ten before I ran out of output in the quadrature path - you'd need a si ngle-side-band style phase shifter to make that work well, and the artifici al reactive current would start degrading the harmonic content for any sign ificant frequency shift.

To lock the frequency to a crystal reference one wouldn't need to inject ve ry much current at all - the real inductor is a very heavily gapped ferrite core, and the real capacitors good quality film, so the natural frequency won't shift much with temperature

ase shift circuit and obtain very clean sinusoidal waves.

It's usually done with a Wein bridge, and you've got to use feedback to set the gain exactly right to stabilise the amplitude without clipping.

It's a low Q circuit, so you've got to be a bit careful if you want really low harmonic content. That approach can yield very low harmonic content, wi th the third harmonic more than 120dB below the fundamental - the people th at did that used an LME49710 to provide the bulk of the gain.

It's not a flexible circuit, and you'd have fun trying to phase-lock it.

If you think that you are generating a "very clean sine wave", it is probab ly because you haven't looked at the harmonic content. You might find a bri dged differentiator handy if you wanted to do that.

The write-up in "The Art of Electronics" is better - page 280, Figure 5.23.

most of us have seen that thing of beauty, as you keep pointing out.

I've never posted it. My long term plan is to try and publish it, once I've got the real circuit assembled and tested and have some confidence that it will work more or less as well as the LTSpice simulations. Academic journa ls don't like publishing stuff that has been published elsewhere, even in a rubbish venue like this one.

I'd be happy to e-mail the circuit diagram to anybody I trusted - which doe sn't include you, Jim or John Larkin.

depending on your point of view and the sign of gain.

the frequency.

Ok, yes I read the complete pile of what ever. So I guess I should give credit to the LME49710, since it's obvious you'd be lost with it.

All of the accuracy you boosted was due to that component? Hooray for the semiconductor engineers making your task a no-brainer, and I say that lightly. Have a hell of a day.. Jamie

I'm getting two pair from the VA. Computer, and a pair for close-up work for reading, and working on equipment. My old bifocals are still OK for driving.

On Sunday, 24 November 2013 09:16:46 UTC+11, Maynard A. Philbrook Jr. wrot e:

a negative resistor circuit onto a LC and let it self oscillate. This would be instead of sweeping it.

ibly simply turn this into a VCO... but I haven't gotten that far yet.

g on the 17th November 2013 at 05:06:39 and 05:47:53 UTC+11, in the origina l "Tuning an LC" thread.

e simulation, but not yet in real life, because I haven't get soldered the bits together). It needs a 90 degree phase shift network (which Jim doesn't seem to have noticed yet) and a high-output-impedance - current source - d rive to push the artificial reactive current into the tank circuit where it looks like either a parallel inductance or a parallel capacitance, either positive or negative depending on your point of view and the sign of gain.

shift to obtain oscillator for decades, what makes your so special?

an LC tank circuit to set the nominal oscillation frequency, a NatSemi/TI L ME49710 - which is a very low distortion op amp - to do the bulk of the wor k of sustaining the oscillation, and programmable gain parts to adjust the (more or less) in-phase loop gain to maintain exactly the desired amplitude without injecting too much in the way of higher harmonics, and in the quad rature loop gain to adjust the frequency.

ctor of ten before I ran out of output in the quadrature path - you'd need a single-side-band style phase shifter to make that work well, and the arti ficial reactive current would start degrading the harmonic content for any significant frequency shift.

t very much current at all - the real inductor is a very heavily gapped fer rite core, and the real capacitors good quality film, so the natural freque ncy won't shift much with temperature

phase shift circuit and obtain very clean sinusoidal waves.

set the gain exactly right to stabilise the amplitude without clipping.

lly low harmonic content. That approach can yield very low harmonic content , with the third harmonic more than 120dB below the fundamental - the peopl e that did that used an LME49710 to provide the bulk of the gain.

obably because you haven't looked at the harmonic content. You might find a bridged differentiator handy if you wanted to do that.

.23.

ce most of us have seen that thing of beauty, as you keep pointing out.

I've got the real circuit assembled and tested and have some confidence tha t it will work more or less as well as the LTSpice simulations. Academic jo urnals don't like publishing stuff that has been published elsewhere, even in a rubbish venue like this one.

doesn't include you, Jim or John Larkin.

credit to the LME49710, since it's obvious you'd be lost without it.

No. the major source of harmonic distortion in the circuit is the hysterisi s of the ferrite core, even when heavily gapped. LTSpice and the John Chan model put the third harmonic content some 104 dB below the fundamental.

The top-up current is about 43dB below the circulating current in the tank, so the LME49710 is definitely an over-kill.

he semiconductor engineers making your task a no-brainer, and I say that l ightly.

I'm sorry to see that your reading comprehension is as defective as ever.

Well the button was so small the assembly fit comfortably inside the ear and did not have to wrap around the ear. I guess we could have stuck the AA cell into the ear, but that would look a bit like a stick of dynamite pprotruding.

Hardly the subject.

Useless. Even the early ones I saw were rechargeable. Who needs audiophile quality on telephone gear? That's the ultimate in audiophoolery.