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What's the best way to receive ultrasonic signals?
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yannick_33:
Hello Mark03,

what is this "daughter-board for the STM32L476 "Discovery" kit" ?

Thank's, Yannick.
mark03:
Hi Yannick,

The daughterboard was my own custom design (see attached PDF schematic).  It is slightly more complicated than necessary because I was trying to make a generic front-end not only for bats but also a VLF software-defined radio and anything else that could use a 1 to 2 MSPS ADC.  This is not a viable approach unless you have plenty of electronics (and surface-mount soldering) experience and are prepared to dig in and customize the HW/SW to your own liking.

There are much simpler circuits which can do a good job; I designed this one last year for some high-school kids:
https://www.eevblog.com/forum/projects/critique-my-ultrasonic-translator-circuit/
coppercone2:
If you go SMD I noticed that the ultrasonic microphones (one of which is no longer produced) seem to have a larger mesh-covered opening, while the audio ones have a pinhole.

https://www.digikey.com/products/en/audio-products/microphones/158?k=microphone&k=&pkeyword=microphone&pv41=98&sf=1&FV=ffe0009e%2Cyr100Hz+%7E+100kHz%7C2145%2Cyr100Hz+%7E+80kHz%7C2145%2Cyr50Hz+%7E+40kHz%7C2145&quantity=&ColumnSort=0&page=1&pageSize=25
mark03:

--- Quote from: coppercone2 on October 22, 2018, 07:16:44 pm ---If you go SMD I noticed that the ultrasonic microphones (one of which is no longer produced) seem to have a larger mesh-covered opening, while the audio ones have a pinhole.

--- End quote ---

It was after seeing only a handful of Knowles MEMS mics rated for ultrasound that I inquired with technical support.  I was told that the difference is mainly in characterization; the engineer claimed that all bottom-port analog MEMS devices have a similar ultrasonic response.  I've used Invensense ICS-40720 with success.

It would be a useful project to come up with a test apparatus for ultrasonic sensitivity characterization.  Only relative, not absolute.  A short spark discharge at close range might work, but you'd need a $$$ microphone with known ultrasonic response to test it first, and I'm too cheap for that!
coppercone2:
Well a problem you will get is that the microphone may couple electrical fields through its wiring rather then just the acoustic signal if you use something like a spark.

I shielded the crap out of one of those microphones on a stick to make a pockey probe rod (its some where in the coppercone posts I think).

Also with those mics, some vendors sell the standard ones rated till 40KHz (rather then the 20 on digikey)

I have yet to buy the broadband ones.. but I do have some 'ultrasonic transducers' from ebay, the standard type that look like a little dish under a mesh screen. I think if you connect them to a function generator they produce some noise, and they can receive noise too.
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