Is this ultrasonic insect repeller actually ultrasonic? - Page 1
Forum section: electronics / beginners

author: John_doe
author_rank: Regular Contributor
timestamp: June 26, 2019, 12:36:39 pm
content: 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.

author: not1xor1
author_rank: Frequent Contributor
timestamp: June 26, 2019, 04:40:44 pm
content: it looks like a quite ill designed capacitive power supplywhile 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 diodein any case ultrasounds don't repel insects and in some cases might even attract themit is a sort of scam going on since several decadesin this case it is likely to be a double scam since I bet there is no ultrasound

author: John_doe
author_rank: Regular Contributor
timestamp: June 26, 2019, 07:58:10 pm
content: 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.

author: John_doe
author_rank: Regular Contributor
timestamp: June 26, 2019, 09:09:02 pm
content: More photos:

author: Zero999
author_rank: Super Contributor
timestamp: June 26, 2019, 10:02:09 pm
content: 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.

author: Marco
author_rank: Super Contributor
timestamp: June 26, 2019, 10:05:14 pm
content: Insects don't give a shit about ultrasonics any way.CO2 baited traps can work, but I don't know any consumer versions and the chemical plug in ones too (bigclive recently took one apart).

author: John_doe
author_rank: Regular Contributor
timestamp: June 27, 2019, 08:55:50 am
content: Thank you Zero999, where is the 2KHz coming from if the frequency is 100Hz?Another question: What is the maximum voltage drop on the speaker? I'd like to connect my DSO138 scope (50Vpp max) directly to the speaker to see the waveform but on devices powered from 220VAC I'm a little nervous (both for my safety and the safety of my DSO138), do I need a voltage divider?

author: Zero999
author_rank: Super Contributor
timestamp: June 27, 2019, 09:10:46 am
content: Quote from: John_doe on June 27, 2019, 08:55:50 amIt'll be the resonant frequency of the piezo transducer, which looks like an ordinary audible one, that typically has a resonant frequency of 2kHz.You'll need to connect this circuit via an isolation transformer or use a differential probe, to safely connect the circuit to an oscilloscope.

author: John_doe
author_rank: Regular Contributor
timestamp: June 27, 2019, 02:42:09 pm
content: Quote from: Zero999 on June 27, 2019, 09:10:46 amI have neither...What will happen if I just connect the DSO138's terminals across the piezoelectric transducer? Of course, I will do it very safely - I will solder leads to it and affix everything with good isolation before I'll connect it to the power.I should also mention that the DSO138 is not a normal scope, it's more like a toy, and mine is powered from a battery and is not connected in any way to the house earth/ground.

author: StillTrying
author_rank: Super Contributor
timestamp: June 27, 2019, 04:17:23 pm
content: There's no need for a scope, it doesn't do anything useful, perhaps the plasticky smell scares the insects away. In winter you might find insects living in it for the warmth."An electronically challenged friend asked me to buy him an ultrasonic insect repeller from Aliexpress."Let him test it.The only interesting bit is how the LED survives the reverse voltages.

author: Zero999
author_rank: Super Contributor
timestamp: June 27, 2019, 08:58:40 pm
content: Quote from: John_doe on June 27, 2019, 02:42:09 pmThat's a bad idea. The oscilloscope will float at the mains voltage and could give you a nasty shock, if you touched it.How about placing a microphone and amplifier near the piezo and looking at the waveform with the oscilloscope? That's much safer and will actually show you the sound wave being produced, rather than the electrical signal to the traducer, which might not match it perfectly.

author: Ysjoelfir
author_rank: Frequent Contributor
timestamp: June 28, 2019, 07:01:59 am
content: Quote from: John_doe on June 26, 2019, 09:09:02 pmHey, that thing is gorgeous! Its Nno toxic, environment-triendly, Sare and dorless!Also it is moisture proof and waterproof, but don't clean it with water or a damp cloth, it may break!And don't forget to not make strong striking on it. Not-so-strong striking is ok.What a pile of crap. Dispose of this thing, the best it will do is light up your friends house.

author: John_doe
author_rank: Regular Contributor
timestamp: July 01, 2019, 02:00:51 pm
content: Quote from: Ysjoelfir on June 28, 2019, 07:01:59 amThat's standardChinglish, I've grown used to it by now so it's barely amusing (Well, except forthis photofrom a hospital in China which had me laughing out loud).Quote from: Ysjoelfir on June 28, 2019, 07:01:59 amUnfortunately, it is not mine to dispose of.Quote from: Zero999 on June 27, 2019, 08:58:40 pmThanks again Zero999, I took your suggestion and tried to connect an electret microphone to my scope but I struggled to get a clean signal. Nevertheless, even with a "dirty" output you make out enough:It looks like the signal is occurring every 5 divisions, so, exactly 100Hz (2ms per division), but the signal isn't clear enough to differentiate 1 cycle of the resonant frequency, even though 0.25 of a division (2KHz) seems about right.