Awesome project! I’m happy the author figured it out! I feel vindicated :)
:)
> that works in the air, using off-the-shelf components (< $100).
I can try to find that papers if you would like.
Would really like to see papers on the subject, because I don't really understand how you can use lasers in opaque materials. Will also look at my test to see if it's really about that.
I get it, it's a hobby project, but I feel the knowledge of analog electronics is getting lost in a way (and yes the analog people are the worse at explaining things - I think I saw YT videos more informative than whole university courses)
There were definitely well-known circuits for driving transducers, but I had to improvise to make a circuit small and simple enough to build 100 of them.
Building new circuits requires tinkering and many tries, regardless of the builder's knowledge.
Yes, maybe an Opamp that works at 40V could have worked (with an appropriate feedback config), but your end result looks ok. I'm just saying that putting the transducer in the emitter was a non-starter (as you correctly pointed out)
> Building new circuits requires tinkering and many tries, regardless of the builder's knowledge.
Absolutely, I'm not denying it :) It's a great job nonetheless
Medical 3D ultrasounds are a thing:
https://en.wikipedia.org/wiki/3D_ultrasound
That doesn't take away anything from how cool this project is though!
Cool. For which school was it? And Which year? (I'd like to get the subject and read it actually)
The subjects have not been officially published. But here's a scanned copy:
https://www.cpge-paradise.com/Concours2021/PhysPSI.pdf
It's in French though!
The first option isn't the good one. Ultrasounds are already used in car parking assists and people trying to improve them would have gone the same route as I did.
I don't get it. What do you mean by that?
[didn't read your article, your claim has put me off, sorry]
-- use an electric spark gap as the wideband acoustic source
-- use 3 simple electret mikes on 3 axes. Mikes don't need to be high quality (spark intensity can always be raised as necessary), so they were hand-assembled using metallised mylar film (used nowadays to pack some food, or ESD-sensitive electronics components).
The rest was data processing.
But another reason (which would be valid for a resistive load as well) is that anything plugged into the emitter will have its impedance "reflected" to the base.
Even if you're talking about a digital circuit you need to think about transistor biasing. A pure capacitive load on the emitter means no biasing.
One of the ways you could work around this is to have an inductor in parallel with the transducer so it would resonate at the frequency you want https://en.wikipedia.org/wiki/LC_circuit (though not very practical to your case) - but ideally this would go on the collector, not on the emitter
Your 3 transistor solution is ok for the most part. Maybe it's doable with only one transistor but probably would need an inductor and/or wouldn't be too efficient.
(Not the best explanation, but this would require some trial and error and actually thinking a bit about the analog aspects of the circuit)
There are a few limits on what you can scan with only 3 mics. I detail everything in my article. Really suggest you read it.
Though, the emitter is pulsed and I also rely on the fact that it stops resonating after I cut out the power. Unless my LC oscillator has a low Q, it will keep oscillating after I cut out the supply, which is something I'd prefer to avoid.
Correct! You can add a resistor in parallel to reduce Q (but it will naturally "not be perfect" since the transducer is putting energy out as sound waves and it's not really a capacitor.
https://rusneb.ru/catalog/000224_000128_0000488231_19751015_...
-- click on "Skachat' PDF" (second from the top on the left). Unfortunately it is in Russian, not sure whether English translation exists.
This patent seems only for (X,Y) coordinate capture, but the same authors later worked on 3D setups as well.
EDIT: let me know if you need help with translation
https://en.m.wikipedia.org/wiki/Phased_array
Radar is at its simplistic sensing a pulse out and listening for a return. But then the engineers wanted more.. of course home radar would not be really safe.
Cool project by the way.
So it's not properly able to scan an object like I did?
Apart from that, how have you found that untranslated 1975 Russian patent? Google Scholar?
It's impressive what they were able to build with such low-tech.
They exist, except they are more pricey.
they definitely aren’t as cheap as Chinese offers but I always found them to be reasonably priced. They manufacture in Germany.
This seems even lower level, since I was basically using off the shelf components, and you built the whole thing yourself!
Really cool.
[0] https://en.wikipedia.org/wiki/Phased_array_ultrasonics