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transducer or piezo or ??

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MrDEB

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want to produce a 2 tone sound (2khz-6khz) (see deer chaser post) but am lost as a piezo will produce set frequency (internal drive) when voltage is applied.Can a piezo produce variable frequencies?
looking at maybe a VCO to produce the 2-6khz frequencies?
at what frequency is ultrasonic?? or is there really a definite frequency?
This device will be outside thus weather proof.
lost in Salmon, Idaho
 

tcmtech

Banned
Most Helpful Member
Ultasonic is sound frequencies over 20,000 hz.
A piezo can make any frequency you drive it with but are more suited to higher frequency use.
The simplest way to make one variable is to take it apart and remove the inner drive circuits. Then run the 2 primary leads out to an external signal source. The third lead if it has one is part of the oscillator circuit and is not needed. Its the smallest connection spot on the piezo disk.

Then drive it with whatever circuit you were planning to use.
 

dknguyen

Well-Known Member
Most Helpful Member
Ultrasonic starts around 20kHz. It basically starts around where most people can no longer hear the sound.

Piezos are crystals and have a resonant frequency so they won't work too well at anything but that. Cheap ultrasonic sensors work this way. You send a square wave into the crystal with the same frequency as the resonsant frequency of the crystal. THe crystal vibrates producing a sinusoid of it's resonsant frequency (and the fundamental of the square wave) because it filters out all the harmonics.

But there are piezo speakers I guess so they probably make them a bit differently than the ultrasonic transducer ones I'm talking so they don't have such narrow bandwidth.
 
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Sceadwian

Banned
2-6khz? You're not going to tick off the dear you're gonna tick off people. Human hearing is very sensitive in that range.

Keep in mind super cheap toys and many 'talking' greeting cards use piezoelectric speakers. Though some of the better ones use small electromagnetic ones. You're gonna need something over 15khz or people are going to hear it. No idea what a dear's hearing range is.
 

MrDEB

Well-Known Member
Deer hearing = 2-6khz

at least thats what I found.
there are Deer control units that use ultrasonic, water, or turn on a radio.
My plan is to annoy the deer so they DON'T want to be anywhere near the device.
could turn down the volume.
any ideas on what to use for sounding device??
 

audioguru

Well-Known Member
Most Helpful Member
A piezo "buzzer" or beeper has a built-in oscillator. It beeps when DC is applied to power the oscillator. The frequency is the loudest resonance of the cavity in the housing.
A piezo "speaker" is a transducer. It has many resonance frequencies that are loud and other frequencies that are not loud.
 

Sceadwian

Banned
Animals don't respond well to static 'annoyances' they might be frighted away at first but if it doesn't physically cause them discomfort or alarm in some manner they'll eventually ignore it. Try training a cat by yelling at it, then by using a squirt gun, tell me which one works =)
 
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