I have two Beagle dogs
who love to bark. They are especially annoying when we take them for a ride
in my minivan. They get excited and bark, a lot. I saw this ultrasonic
device advertised on TV a while back and then later saw the same device for sale
at a large discount store. I decided to give it a try. In short, it
did nothing for my dogs. I could not tell if the thing produced sound.
There is a slight hiss sound when it is supposed to be producing ultrasound but my
old ears are not sensitive enough to those high frequencies.
Just to be sure, I decided to buy a second unit and got the same results. My
dogs sometimes reacted to the sound, but it sure did not stop them from barking.
The Hi/Lo switch only selects the sensitivity of the microphone switch and does
not change the tone or volume of the sound emitted.
I took the
device apart and gave it a quick inspection. It is powered by a 9v
battery. Snapping a finger in front of the device’s electret microphone
triggers the ultrasound for a few seconds. I measured the sine wave shaped
transducer drive frequency at 28KHz and the Amplitude at 35 volts peak to peak.
That is respectable Amplitude. The ultrasonic piezoelectric transducer is held
inside a sealed plastic case with a cone like speaker. I think the cone is
supposed to help match the piezo wafer acoustic impedance and direct the sound
out through the louvers in the front of the case. Piezoelectric tweeters
are made in much the same way but they are designed for a broad high frequency
response. This device is a single tone producer.
Bark Off Unit
Inside Bark Off Unit
Bark Off Ultrasonic Speaker and Circuit Board
I
measured the current drain at 650ua during standby mode. The current jumps up to
68ma when the ultrasound is activated. That is not too bad. I could see a
555 timer IC on the circuit board and a three pin ferrite core transformer. The
transformer must be used to drive the transducer at a higher voltage than possible
with the 9v battery. The rest of the parts are most likely used to Amplify the
signal from the electret microphone, which triggers a 555 timer one-shot pulse lasting
a few seconds. A transistor oscillator must be used to drive the piezoelectric
wafer at 28KHz, using the ferrite transformer.
I
remember experimenting with sounds some 20 years ago, when I had a neighbor with a
barking dog. I used a 100 watt audio Amp and a signal generator to see if an
ultrasound frequency could be heard by the dog. I used a 50 watt piezoelectric
tweeter with a directional cone on it. The dog could hear the sound alright but
even when cranked up the system to full power; the sound did not stop him from barking
either. I moved the frequency up and down and even tried sweeping tone with the same
results. I got the most attention from the dog when I switched from an
ultrasound frequency to a broadband white noise sound source. A sudden
shissssssss sound made him stop for a few seconds but then he started up again.
Maybe
this product would work on some dogs but it sure didn’t do anything for my dogs.
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