cheap ultrasonic microphone.

[BeBuLamar]

I want to check the frequency of the ultrasonic pet repeller. It's supposed to generate ultrasonic sound up to 65kHz. What kind of cheap mic/transducer I can use? I will be using a scope to look at the waveform.

[BradC]

I know cheap electrets used to go to 40ish KHz, but never went higher. If I were testing a pet repeller I’d probably use my Labrador.

Edit : I should, have said *I* never went higher. They may.

[CatalinaWOW]

If you don't care about amplitude you can probably is one the ubiquitous piezo discs.  They typically resonate in the neighborhood of 40 kHz and these response above that will fall off at about 40 dB per decade.  That should leave something to see at your nominal frequency.

[CaptDon]

Those Motorola piezo tweeters have a natural resonance around 25KHz and I am sure will produce usable detected output at 65KHz. There are transducers designed for 40KHz that were designed for remote controls. They were available through Radio Shack, Lafayette and Philmore. Probably easily found on Ebay.

[BrianHG]

Even the cheapest electret mic will go beyond 40Khz, even up to 75Khz.

You will need to keep your preamp right up at the mic.
Use a slightly higher drive current, though test as it may not be needed.
Use a transistor or mosfet wideband first stage amp before your opamp.
Remove the black fluff covering the front of the mic.  (Remember, in the outdoors like this, wind will wreak havoc..)
Remember, ultrasonic sound is more directional than lower frequencies.
The mic will not be completely flat at the high end due to it's internal design.

[Zero999]

I want to check the frequency of the ultrasonic pet repeller. It's supposed to generate ultrasonic sound up to 65kHz. What kind of cheap mic/transducer I can use? I will be using a scope to look at the waveform.

If you're talking about a rodent repeller, then they don't work anyway. Shawn Wood's channel on YouTube shows they're all bunk.




https://mousetrapmonday.com/videos/proof-that-ultrasonic-pest-repellers-are-a-scam-class-action-lawsuit-for-fraud/



If it's for mosquitoes then may be.

[Kleinstein]

Many of the small (e.g. < 6 mm) electret mictorphone will go to rather high frequencies.  The performance can however vary as some have an extra capacitor to limit the bandwidth. Chances are the cheap ones will skip the capacitor for cost reasons.  For just the frequency one could also tolerate a reduced sensitivity.

[CaptDon]

It is sad to see the shit knock-off of a once trusted name!! Bell+Howell IS NOT Bell & Howell. Just like Zenith with the plain Z is not the former Zenith with the lightning bolt Z. Just more off-shore garbage headed to our landfills. Need I set more examples?

[BeBuLamar]

My wife wanted to get them. I don't think they work but curious as to what kind of sound they output. Yeah I can connect the scope directly to the signal wires but I don't want to take the thing apart because my wife would say I made them not working.

[CatalinaWOW]

Finding out they put something out is a start.  But who knows how much it takes to repel rats, or how it propagates through your house.

Two anecdotal examples to illustrate the problem.

1.  When I was young I could still hear very high frequencies, 22 kHz or more.  Including the sound from the ultrasonic motion detectors in a major department store.  Probably used only at night, but left on 24-7 because most people couldn't hear them.  But they were very annoying to me and I would avoid that store.  Moral: The device may work on a small subset of rats.

2.  I worked once in a large building that had regular fire drills.  The alarm was a piercing, pulsing braap with a dominant frequency probably in the 8-10 kHz range.  But particularly at one location near the exit was of incredibly high intensity.  Rock concert loud or louder.  It was physically painful to leave the building even with ears covered.  Moral: maybe these devices work on many or most rats at a high enough power level.  Lots of experimenting to find out if your devices are noisy enough to do the job.

[BeBuLamar]

I am just curious at what kind of frequency they put out not so much for intensity.