I Can Haz Rezonance! [Caution: May contain grandiosity]

[tcepsa]

I spent far more time than may have been prudent playing with electronics last night.

I now have a square wave generator in the form of an astable 555 timer circuit (I've wanted one of those for years!) If I remember right, I could also use that in combination with the proper op-amp arrangement to make a triangle-wave generator (square wave + integrator = triangle wave).

This is, however, merely the means to a larger end. I then went on to try to get that to drive a resonant LC circuit. This consumed the majority of the time, and while I am not sure I have come out all that much wiser for the experience, I think I finally got to the point where I understand enough about what it's doing to actually attempt to create a receiver for it. Yes my friends, I have taken up my electronic lance and am heading full tilt at the windmills of wireless power transfer.

The irony of all of this is that it, in turn, is merely a cog in my greater scheme for an advanced human-computer interface device, which would be much more convenient if it were entirely wireless and did not need a battery (or could run off rechargeable battery and run or charge off of wireless power).

I was actually inspired to look into this by adularia's ongoing project, as I am hoping to do an implementation of that concept, but wireless and probably with a different sensing mechanism.

It was a good night ^_^

~does rough time estimates in head~ Yeah, at least 5 hours, pretty much straight. It wouldn't have been too bad, but there are other things around the house that also need doing. I was reasonably good about most of them; I mowed the lawn until it got too dark to do so, and I did cat and dog maintenance, but I really probably should have had more for dinner than a few handfuls of corn chips and a bunch of water kefir. Then again, I had a pretty big lunch, so it probably balanced out reasonably well. Still, the kitchen is a frightful mess, and it's more the principle of the thing. I told myself that I'd stop and work on the kitchen at 10. And then I moved it back to 11. I revised that to be that I'd get the dishwasher emptied before I went to sleep. The dishwasher finally got emptied this morning. I'm not sure whether to be annoyed or concerned about my apparent lack of willpower, or pleased with how absorbed I got in the tinkering and how much progress it feels like I've made. Unfortunately it seems to require more mental dexterity than I possess in order to do both.

Comments

[adularia.livejournal.com]

O hai, speaking of my ongoing project -- those diodes, yes! I sent you mail, let me know what you think.

I remain terribly confused by everything I read about wireless power transfer. Beyond, y'know, inductance, which in ITSELF is still kind of goofy.

An attempt at illumination

[tcepsa.livejournal.com]

You shall get a reply e-mail as soon as I finish writing this assuming I don't get distracted by something shiny while attempting to switch tabs ^_^

This is an attempt to unconfuse you a little bit. Feel free to disregard if you're not interested just now ^_^

From what I can tell (and I'm surprised that none of the material I've read on the matter actually uses this phrase, as it helps me a lot to think about it this way) wireless power transfer is simply an application of sympathetic resonance. To steal Wikipedia's example, imagine you have two tuning forks and each resonates at a frequency that is equal to or harmonic to the other. Stand one up on its end so it's not being damped by anything, then strike the other and hold it near the first, then damp the one you struck and you'll be able to hear that the first has started resonating. This is because the sound waves from the first will impinge upon the second and cause it to vibrate at its frequency.

Now, to completely switch imagery, consider a single oscillating system: a swing at a playground. If you push the swing and it's just sitting there, it will start to swing (oscillate). If you don't push on it again, it'll eventually come to rest. If you push it again, but at the wrong point in its swing, you'll slow it down or stop it. Finally, if you then keep pushing it with the same amount of force at just the right moment in its swing, the amplitude of its oscillation will increase to some maximum (it will go higher and higher until it can't anymore, and then it'll keep going that high as long as you keep pushing it when it swings back to you).

So now think about the oscillating system that is a simple resonant circuit: an inductor and a capacitor. If you apply an impulse (quick spike of energy, analogous to pushing the swing), then the voltage across the inductor will oscillate for a time and eventually fall to zero, damped by the inherent resistance of the circuit (just like giving the swing a single push). If you apply an impulse at just the right time each oscillation, then the circuit will continue oscillating indefinitely (just like when you continue to push on the swing when it comes back to you).

So now we have a resonant circuit hooked up to a square wave generator, which isn't actually providing impulses but it's close enough for now I think because each time the wave goes from low to high or back down it is very similar to providing an impulse (think of it like two people pushing a swing, one on each side. The first person pushes it, then the second pushes it back--it's not quite analogous, but it's close enough for this I think)

Now imagine a second resonant circuit that resonates at the same frequency (for simplicity, we'll say it has the same L and C values as the first). We now take advantage of Faraday's discovery that when magnetic flux lines cross a conductor, an EMF is induced in that conductor. Since the first resonant circuit contains an inductor, and because of the nature of inductors, the first resonant circuit is causing the fluctuation of magnetic flux lines back and forth in its vicinity, and they are fluctuating at the same frequency that the circuit is resonating at. If you put the second circuit nearby (like with the tuning forks) with the right orientation, then the magnetic flux lines will cut across the wires of the inductor and generate an EMF in the second inductor having the same frequency as the oscillations of the first circuit (the second swing is being pushed by... an invisible person? The analogy breaks down a little here ^_^; ) Better yet, since the second circuit has the same resonant frequency at the first, and the induced EMF is at that frequency, then the second circuit will have its own set of oscillations induced in it as well.

Clear as mud, eh? ~grin~

[nminusone.livejournal.com]

If you only need a *crappy* triangle wave you can tap one off the capacitor itself, then buffer it if needed. Or (by some weird coincidence) I was thinking the other day that you could add a constant current pump to the basic 555 circuit and it'd generate *good* triangle waves right off the capacitor.

I read that people who live near/under power lines sometimes lay big loops of wire on the ground to steal electricity. Of course you have to get the voltage right. ;)

[adularia.livejournal.com]

Wasn't there a Mythbusters about that?

[nminusone.livejournal.com]

I have no idea... I read about it in a book about security in various types of engineered systems. At least I think that was it.

[wetdryvac.livejournal.com]

Sounds like fun... and to annoyed/concerned/pleased...

YesNo?