> Holy hellpants. A fire extinguisher just blew up in my basement and the
> whole place looks like a sandstorm just went through. I wasn't around for
> the "BANG" but I'm told it was pretty spectacular. Looks like I won't be
> bringing the phased array to Hive tonight. :( Maybe I can catch MMMM on
> Monday.

> I've partially implemented a couple of things but haven't had time to tie
> them together yet: a new lookup table will make quick work of converting an
> ADC reading from a pot into an element delay. I wired it differently so I
> can use all 10 elements. Minor tweaks but they'll help improve it. I have
> some ideas about how to make it quieter in the off-beam directions, we'll
> see how they go. I also have an SPL meter so I can try and quantify the
> effect at least a bit.

> The directional sound thing is fun but for me the interest is more in
> phased arrays. After all there are other ways to do directional sound
> (parabolic reflectors etc), but it's the phased array that brings the
> flexibility of electrically steering the beam on the receive or the
> transmit side, etc. I'm interested in learning more about the practical
> side of beamforming, and maybe eventually trying to do something cool with
> it like make a 3D ultrasonic ranging sensor (either for air or water) or
> demonstrate some level of seeing inside solid objects. Somebody in the
> hobbyist world needs to get on it, there's no reason we can't. If anybody
> is interested in lending any type of hand, feel free to email me directly.

> -Dave

> On Wednesday, May 9, 2012 11:12:23 AM UTC-4, pezman wrote:

> > Pretty cool

> > For your idea on directional sound, I think that if you amplitude
> > modulate an ultrasonic carrier, it is audible (and highly
> > steerable).

> > On May 7, 7:19 pm, Dave <dgsh...@gmail.com> wrote:
> > > > Whoa, very cool man. I'm definitely interested in watching the
> > evolution of this project.

> > > Don't get your hopes up too high, I'm no expert and I was unable to find
> > a half hour to work on this all weekend!

> > > > As far as the "clicks" - are they actually just single burst like a
> > single wavefront or is it a chirp

> > > I haven't yet recorded one to see it, but my transducers have a resonant
> > frequency around 3.3kHz. So if I drive it with a square wave (5v / 0v /
> >  5v...) at that frequency it will emit a whine. When you apply a voltage to
> > it it acts like a capacitor: charging it up causes it to deform, producing
> > a sound much the same way a speaker would if you energized it. The piezo
> > requires no power to hold that deflected position once charged up so
> > there's no risk of blowing the piezo if you just leave it high (don't try
> > this with a speaker!), no current will flow. You can then discharge it to
> > produce the tail end of the wave, completing a full cycle. The transducer
> > will have some amount of ring to it at its resonant frequency after you
> > stop driving it. Think of it like pushing a swing: one push will get it
> > going at its resonant frequency, and you can theoretically push it back and
> > forth at any rate you want, but anything far from the resonant freq will be
> > lots more work.

> > > > at a certain frequency? I'm not at all familiar with these devices so
> > I may just be talking out my ass, but I wonder at the use of having
> > different transducers chirp at different frequencies - perhaps ones that
> > are distantly harmonically related so their peaks would all combine
> > constructively at some desired distance away so you could have a point of
> > concentrated acoustic energy.

> > > With a phased array you can time the element phase delays such that all
> > the signals hit the same point at once, you basically just use a parabolic
> > phase delay map, focusing it like a sound lens. This only works in the near
> > field, I doubt it's possible to do something like this in the far field.
> > Your transducers have to 'surround' the target to some degree so the waves
> > aren't all parallel. My current code just assumes far field with parallel
> > wavefronts: delay = element spacing * sin(azimuth angle) / speed of sound.

> > > Dunno what I'll have time for, but it's sure fun thinking about the
> > possibilities. Here's one for a cheeseball ultrasound system: you have an
> > array of receivers (let's say 4x4, very crude), pressed against the skin.
> > In the center just have a rubberband that you pull back and snap. That
> > sends a single wavefront into the body in all directions, and you capture a
> > couple of ms of signal from each receiving element. Now in software after
> > the fact you can go through, 'listening' in each direction (azimuth and
> > elevation), maybe even sweep through different focus distances. You can do
> > all the heavy (but dead simple) processing on a PC or Gumstix or whatever.
> > Might be cool. Albeit slightly painful. ;)