Ultrasonic noise generator circuit

[DaveInDurban]

I need to make something to annoy monkeys - I'm in Durban, South Africa - and I understand that they do not like ultrasonic noise. If I take a basic noise generating circuit (e.g. reverse biased base-emitter of an npn transistor, or zener diode, amplified with a single transistor amplifier), and simply feed it thru an RC high pass filter to a cheap 8 ohm tweeter, will it generate enough noise between say 20kHz and 40kHz? I don't know the frequency range of the reverse-biased junction.

I can go ahead and try it, but I don't have an oscilloscope, so I can't check that it is producing a signal, and I won't be able to hear it if it does. I think there are commercial noise makers to chase away dogs, so hopefully there is a circuit that is known to work.

This is meant to be part of an automated garden watering/monitoring system: I am adding motion detectors and the monkey deterrent to keep monkeys out of the garden.

 

[atferrari]

I know this is not answer to your question but keep in mind that with US you could eventually affect kids and babies (who maybe could not express how bad they feel). Dogs also.

 

[Tony Stewart]

You may be interested in Steve Gibson's forum for dog lovers that dislike nuicance sounds.

https://www.grc.com/tqc/thequietcanine.htm

I think steady white noise will sound like rain, but random pulsed burst of ultrasound noise may spook them.

Also look up digital white noise at any frequency using simple PRSG circuits on google images.

 

[DaveInDurban]

The monkey repellent, if it works, will work like a burglar alarm: turned off when people are around & on when away, so babies and people shouldn't be an issue. Dogs shouldn't be in the garden, but if they are, and they don't like the sound, presumably they'll also move away. But I would monitor it to see if it is having a bad effect. I already have CCTV on the garden to check on the monkeys.

The pulsed noise suggestion makes sense; it shouldn't be difficult to add.

I'm going to give it a shot and see if the monkeys react. My other concern is blowing out the tweeter - I have no idea how far I should drive it, but I'll start small and work my way up.

 

[audioguru]

A cheap tweeter has trouble producing high audible frequencies. It will not produce ultrasonic frequencies.
Your circuit has nothing to cut low frequencies so its noise will be wideband which will blow out a tweeter.

 

[dr pepper]

Motorola ksn series piezo tweeters are good for making an ultrasonic racket, power rating is tricky as they are rated for music program material.
Like you say start low check to see if the piezo is warming up and increase, you'll probably find the piezo will take a lot.

 

[audioguru]

The specs for the piezo tweeter are here:

 

[AnalogKid]

Your two schematics both are low-cost white noise generators. These make some energy at ultrasonic frequencies, but you will get better results with a simple oscillator operating above 25 kHz, or a swept oscillator in the 25 to 50 kHz range. This can be done with two 555's. Also, nothing puts out the watts like a piezo tweeter. But confirming that this is operating will be difficult without a scope.

ak

 

[Dick Cappels]

I found that an NE555 set to oscillate at about 20 kHz and fed into a tweeter with a 30 watt driver is enough to keep my wife out of this part of the house. No need to use a random noise generator when square waves (or whatever they are after passing through the tweeter) can induce plenty of distress. Using a square wave also frees the circuit and transducer from having to handle frequencies below that in which you are interested -making the high pass filter un-necessary.

 

[dr pepper]

The other thing is piezo tweeters act as a filter, they have high impedance at lower frq's, thats why they dont need an xover, chucking white noise in will still mainly produce high freq sound waves.

Glad to see you frequent this forum mr cappels.