Need help with designing a ultrasonic reciever for next years science fair project

[Brhodes0627]

Hi, I am new here. My mom used to work in the electronics field, so she agreed to help me with my project. and sent me here

My project is to build a ultrasonic receiver in the 20 to 50khz range to record my pet rats communication, and to then try to catalog the sounds into a virtual rat dictionary. e.g. how they sound when they want food, when they sense danger, when they are playing. I have seen schematics for receivers, but most of them output to LED displays. I am trying to find a way to make it so i can actually hear how they really sound to each other. This is where i got lost. I am not sure how to convert the ultrasound output to audible sound. Any help would be highly appreciated. Also, quite frankly I would like to have a really good schematic for an ultrasonic receiver if someone has one. My mom is capable of etching boards, procuring parts, programming chips....etc. However, she does limit my funding on projects, so I can't really afford to make too many mistakes on the electronics end. My project won't be due until next April, but because the actual cataloging and deciphering of the sounds is the major part of my project I would like to build the electronic part of it this summer so my data pool is huge when I publish my conclusions. TY in advance for any help, ideas, schematics.

Oh, and whatever you send, my mom is not cool with anything that also transmits as we are not trying to scare the pets, or talk to them. She got worried when she saw that ultrasound trancieeirs are used as pest control, because these rats are family pets, and we would NEVER allow anything that would harm or scare them.

 

[BradtheRad]

I once saw a project like you describe. It allows us to listen to bats, crickets, etc., directly.

It uses a 40 kHz transducer as a microphone (even though they're normally intended for something other than that). These are inexpensive at mail order electronics suppliers.

An internet search shows other devices might be better. See 'durhambats.org.uk':



The transducer detects ultrasonic sounds in the range that humans cannot hear. You amplify the signal.

Then you modulate it with a sine wave of an intermediate frequency. The above link says 20 kHz.

The output is sounds that we humans can hear.

The process (as I recall) is similar to a radio carrier being modulated with an intermediate frequency, and then modulated again to bring the signal into the audio spectrum. A method known as heterodyning.

 

[Brhodes0627]

Thank you so much, that clears part of it. My parents had not heard of heterodyning (one of them is an aircraft mechanic, the other one is avionics certified), but by looking that up I found frequency splitting and time division, which they are somewhat familiar with. The bat detector thing helped big time. because I think i found one that would work if I modify the output. My parents said they can identify the output end of the circuit, but are not sure on how much they will help me with constructing the audio part if I don't do some leg work

Basically my mom said we should now buy a already existing bat detector and work on switching the output to audio with frequency division and time expansion circuits as described on

So that leaves me 2 questions. Is it legal for me to modify someone elses design? (in my mind it is like putting a different set of headphones into an MP3 player). My second question is how much the people here can or will help me with the output circuit design, because my mom and dad both said they will, but it is starting to get into heavy engineering, and they have both been out of the field for a while.

Once again, TY, I have some new ideas now. It is just that my science project is not IF I can build this.....it is the data I record after I do, and what I do with it.

 

[BradtheRad]

Is it legal for me to modify someone elses design? (in my mind it is like putting a different set of headphones into an MP3 player).

For experimental purpose it's all right. However I don't know which is easier, to find your way around a commercial unit's circuitry, or to make your own.

An electret mic will be cheap. Its signals are easy to amplify using a transistor or op amp. An electret is mentioned on that webpage as being able to pick up ultrasonic sounds.

For the heterodyning method, there are IC's which can produce a sine wave, at adjustable frequencies.

You may only need to add a headphone jack (or an audio amp and speaker).

The frequency splitting and time division methods are more involved.

My second question is how much the people here can or will help me with the output circuit design, because my mom and dad both said they will, but it is starting to get into heavy engineering, and they have both been out of the field for a while.

There are many knowledgeable folks at this forum who could help. They like it when you post schematic diagrams and photographs.

 

[FvM]

Identifying a suitable microphone and designing the signal processing respectively recording are different topics.

The only wideband ultrasonic microphones I'm aware of are expensive professional types like B&K 4439 **broken link removed**

Usual ultrasonic transducers are resonant types with a maximal bandwidths of a few kHz. Cheap electrete microphones are only specified up to 20 kHz frequency. They possibly have a certain sensitivity in the ultrasonic range, but it will be difficult to get a specification.

For the signal processing, digital acquisition with 192 kHz sampling frequency can provide a flat response up to 85 kHz. The signals can be analyzed, frequency shifted or transposed with digital audio signal processing tools.

P.S.: I see, that the "bat detection" link has some useful information about microphones.