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Is this ultrasonic insect repeller actually ultrasonic?
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John_doe:
Howdy folks.
An electronically challenged friend asked me to buy him an ultrasonic insect repeller from Aliexpress.
When it arrived I opened it out of curiosity.

At first it looked like this thing produces sound with a frequency of the mains input (50Hz in my country).
But when I thought about it I realized I know almost nothing about resonators/oscillators/multivibrators, so here I am asking people who do.





not1xor1:
it looks like a quite ill designed capacitive power supply
while the high frequency oscillator (ultrasound) might be integrated in the loadspeaker it is likely it just does nothing apart switching on (until it prematurely dies) the LED diode

in any case ultrasounds don't repel insects and in some cases might even attract them

it is a sort of scam going on since several decades
in this case it is likely to be a double scam since I bet there is no ultrasound  :-DD
John_doe:
I also believe that ultrasonic sound waves do not repel anything (at least not at these wattages). The reason being that I never found any reputable scientific articles confirming this theory, and that is what I told my friend when he asked me to buy the thing, but he replied that "A work colleague has it and she swears it works!" and I'm not in the habit of pushing my beliefs onto others.

I should mention that when powered on this device makes an audible sound. It sounds low-frequency to me but I'm practically tone-deaf.

As for something being integrated into the buzzer, it didn't look like it but I'll take a few photos later.
John_doe:
More photos:


Zero999:
No, it won't produce much ultrasound. It's just an ordinary piezo transducer which will produce 2kHz clicks at double the mains frequency. The LED will convert the mains to a squarewave and the transducer will produce a click on the rising and falling edges, hence double the mains frequency.
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