SparkFun Forums

[sryabinin]

Hi everyone, I am working on a project trying to make whats is basically an ultrasonic wave detector. I have bought several ultrasonic transducers (similar to ones used in robots for distance measurement) and was hoping to use those as a microphone for the ultrasonic waves.

Here's my idea. Once the transducer picks up ultrasonic waves the circuit can output some kind of signal, preferably just a change in voltage. This signal I can pick up with LabView via a data acquisition board or a sound card.

The idea is pretty simple, and I think it can work pretty well. But I cant seem to find a good circuit diagram anywhere for what I intend to do. Can anyone help me out? Again, I have no interest in actually processing the ultrasonic waves or anything like that, just simply sending a signal to a computer the moment they are detected.

Thanks a lot for any help or input.

[Philba]

try this http://lmgtfy.com/?q=ultrasonic+circuits

[MichaelN]

I'm not sure what your application is, but if you're looking to use the ultrasonic sensor as a "microphone", bear in mind that most of them have a very limited bandwidth. Most of the time they are used on a fixed frequency.

I assume some manufacturers make "wide" bandwidth types, but they would be harder to find.

[sryabinin]

I actually did a bit of research before I posted this. Main problem is I'm probably not as knowledgeable on circuits as I should be (Mechanical engineering background) and am definitely rusty with this stuff.

I did notice that some of the ultrasonic transducers basically operate on a frequency of 40 kHz. I need something that works on a 25-100 kHz range. According to various papers I found the Knowles FG-3329 has a relatively wide frequency range. This sounds like what I need.

Yes, there are various circuits online, I have seen them. But I have some trouble judging which ones will work for my application. It seems to me they are mostly built for range finding and such, or recording of ultrasonic vocalizations. Neither of which is necessary for me.

[Philba]

look for "bat receivers" or some such name. They are used to down convert bat ultrasonics to something that we humans can hear. I would think they use wideband ultrasonic receivers.

It would help to say what you've already looked at.

[riden]

You haven't described your application, so it is hard to provide specific guidance. More details would help.

Hetrodyne bat detectors use a mixer that takes the microphone input and mixes with a local oscillator operating in the 40 - 60 KHz range. This results in the ultrasonic sound being down converted into the human audio range. Another technology uses a high speed analog to digital converter to sample the ultrasonic input. These devices digitize the ultrasonic signals (sometimes up to 100KHz or more) and then stores it in memory. Once in memory, the play back rate can be adjusted to bring it into the range of human hearing. These are very cool devices and the output is very clean. The noise introduced by hetrodyne detectors is non-existent with these types of receivers.

A hetrodyne detector isn't hard to build, I built one years ago and still use it to detect sources of ultrasonic sound. Here is a page that explains the diffeent types of bat detectors. You can also find sites that have recordings of bats using hetrodyne and down sampling methods.