# Ultrasonic Repeller

#### hazim

Joined Jan 3, 2008
419
Hi all.

I know many sources says that these devices are not practical and so... I have an electronics store and I sell some of them. I've tried on model of a mosquito repeller and it really worked well, this model doesn't cover a big room but only about 3m x 4m maximum. You can see this device on my website, see it in the bottom at the right in this page: http://www.etcenter.co/animal-repellant.html
This one costs about 10$while the one in the first picture in the page should be better as it's much expensive (about 25$).

Now, I'm looking forward making an ultrasonic repeller for very very annoying and tiny flying insects comes in summer at hot weather here in Lebanon. I don't know their name in English. I may let the frequency variable a little like that of the mosquito repeller I tried, and I may put a trimmer potentiometer to vary the center frequency in the experimental circuit.

I reverse-engineered the circuit of that mosquito repeller to benefit from it, and put it in this thread for you to see.

To help you understand the circuit well, when the switch is switched to the other way, the device gives a low frequency sound that can be heard, it's as they say the sound of the dragonfly that makes the mosquito go away when it hear it. The current position of the switch gives the ultrasonic sound, sme sources says that ultrasonic sound is the sound of the mosquito male where mosquito females goes away when they here it (except once a year )

Regards,
Hazim

So I want to hear your opinion, ideas and suggestions, hoping to build a practical ultrasonic repeller for those flying insects that come every summer.

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Joined Jul 7, 2009
1,583
very very annoying and tiny flying insects comes in summer at hot weather here in Lebanon. I don't know their name in English.
We call them politicians here in the US, Hazim.

#### SgtWookie

Joined Jul 17, 2007
22,210
There are LOTS of different types of small flying biting insects. "Sand fleas" were quite troublesome when I was stationed in South Carolina, USA.
This Wiki disambiguation page links to many varieties of such insects: http://en.wikipedia.org/wiki/Sand_flea

I actually built an ultrasonic mosquito repeller many years ago (mid 1960's) from a schematic that was in Popular Electronics (I believe); the article was discarded many years ago. It used a crystal earphone as both the resonator and sound emitter.

Several years ago I picked up a 3-pack of ultrasonic mosquito repellers at a Harbor Freight tool store for a couple of dollars; these devices were about the size of a human thumb, and did seem to keep the mosquitoes away from me when I had one of them turned on.

Mosquitoes don't seem to have been much of a problem for the last several years, so I discontinued using them.

#### hazim

Joined Jan 3, 2008
419
I don't know their name and it's not any of those ones in the link you posted. They are very tiny flying insects, maybe 1/10 the size of a mosquito!! They come around ones head in tens or hundreds and they are really very very annoying..

Mosquitoes are a real problem here in Lebanon. Several ways are used to kill them... but the flying insects that I want to build an ultrasonic repeller for, have no solution since they are outside and need a solution that works outside not like those of mosquito that are used inside

Anyway, where to start? just try that of mosquitoes and adding to trimmer pots to vary the frequencies a little and try.. this is what I think where should I start. That flying insects didn't come yet.. but soon!

I'm thinking how nice and useful this device would be if it worked, especially because it will be small and compact in a plastic box.. light in weight and I may put a rechargeable battery inside the plastic box and so it could be powered or recharged using a wall adapter...

For such an ultrasonic repeller that covers about 2x2m for example, how much do you think its power consumption will be approximately? 0.25~0.5W?

#### hazim

Joined Jan 3, 2008
419
Hi.

I build the circuit without the 555 timer part (the upper part in the circuit diagram in post #1). It's working fine. The first timer of the 556 outputs a signal with frequency about 600Hz, the output is connected to the control pin of the second timer in the 556. The second timer outputs a signal with frequency between 20KHz and up to 40KHz, this frequency is set to a certain value using a potentiometer I've connected in series with R6 where I've changed R6 to 10KOhm. At low frequency I can here the sound from the piezo disk and as I increase the frequency I become unable to hear the sound...

Now there is something that I'm not understanding. The first output signal that is connected to the control pin, won't this make the second output frequency varies (or "waves") like if freq1=0.6KHz and freq2=25KHz the the second output frequency should vary between 24.7KHz and 25.3KHz? isn't this how it works? or the second signal waves at a frequency of 600Hz? Anyway both didn't happened in my case. I measured the second output frequency and it was constant, and on the oscilloscope the signal wasn't waving. I increased the first frequency to several KHz to notice what will happen but only it changes the second output frequency as if I changed it using the potentiometer.

The final signal should varies several hundred hertz to make the device more effective.

Regardsm
Hazim

#### CDRIVE

Joined Jul 1, 2008
2,219
I believe that you're describing 'Gnats'. They're annoying little tormentors that don't bite but can be so thick that you can inhale them. You can also get them stuck in your eyes! Annoying as they may be, I prefer them over 'Flying Teeth' and Skeeters.

#### CDRIVE

Joined Jul 1, 2008
2,219
A piezo is a Hi Z device so I don't think it will do much to dampen the the high voltages developed across the 1mH inductor. I would think that this could destroy components if protection is not used. A reverse biased Diode to GND, on both sides of the inductor, are in order. The Diodes should be placed as close as possible the these nodes.

Edit: I'm not impressed with the parallel drivers either. At least not the way they're currently wired. Even if they were a matched pair, I wouldn't have them share the same base resistor.

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#### hazim

Joined Jan 3, 2008
419
I believe that you're describing 'Gnats'. They're annoying little tormentors that don't bite but can be so thick that you can inhale them. You can also get them stuck in your eyes! Annoying as they may be, I prefer them over 'Flying Teeth' and Skeeters.
No not Gnats. I don't know what are Gnats but googles images for them. I believe you didn't knew what I described because you prefer them over other flying insects

What I described look like the one in the below picture but it's much smaller. I can say that it is about 1 or 1.5mm long only. Very tiny and yes it comes inside eyes sometimes but more frequently inside the ears, and always in hair!

#### hazim

Joined Jan 3, 2008
419
A piezo is a Hi Z device so I don't think it will do much to dampen the the high voltages developed across the 1mH inductor. I would think that this could destroy components if protection is not used. A reverse biased Diode to GND, on both sides of the inductor, are in order. The Diodes should be placed as close as possible the these nodes.
But this is how the mosquito repeller that I reverse-engineered work (the circuit in first post). It doesn't have protection and uses a piezo disk. All the animal/insects repeller devices I have in my store uses piezo.
See the coincidence? I posted my previous reply at the same time you posted

#### CDRIVE

Joined Jul 1, 2008
2,219
I don't have an issue with the Piezo, it's the lack of anti-spike diodes that concerns me. Possibly the Piezo's capacitance and impedance is enough to dampen it. Perhaps, others may have a better handle on this.

#### hazim

Joined Jan 3, 2008
419
Can anybody help me about what I've asked in post # 5? Thanks anyways.

#### hazim

Joined Jan 3, 2008
419
I did this and it is experimental as it has a potentiometer for setting the frequency.

The battery was around 5V and the piezo was giving sound between 18KHz to 31KHz, according to the potentiometer setting. On a new 9V battery, the frequency is between approx. 21KHz and 39KHz, but at 9V source the IC 556 becomes really hot. at the beginning I thought that the circuit works fine with voltage up to 12V or so (without coming into theory and calculation...), but when I connected a 12V adapter to the DC input the inductor and two transistors there burned out quickly and the inductor became very hot. Why the frequency changed at lower voltage? it shouldn't.

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#### CDRIVE

Joined Jul 1, 2008
2,219
I don't calculate the same frequencies as shown on your schematic. As far as I can see your circuit should produce the following approximate time intervals and frequencies.

U2 Output: T=15.5 S F=0.064 Hz
U1A Output: (U2 Ouput Low) T=0.001166 S F=857.6Hz
U1A Output: (U2 Output High) T=0.053000022 S F=18.87Hz
U1B Output: Tc=0.0000242 S Fc=41.322KHz

The values for U1B are center frequency. U1B will ramp above and below this frequency nearly sinusoidally. The rate at which this happens alternates with the output of U2.

BTW, your blown transistors don't surprise me! I'm heading out the door, so this will have to wait until I get back or someone else picks it up.

#### Kingsparks

Joined May 17, 2011
118
Look at post #7 by CDRIVE. The higher voltage probably created spikes the circuit could not take. If the transistor shorted the full current of the power supply shorts to ground through the inductor.

You can't just connect diodes on each side of the inductor as that will chop half your signal out, maybe a couple of the transient filters used in computer power supplies might do the trick. Maybe someone else will know. c

#### CDRIVE

Joined Jul 1, 2008
2,219
Kingsparks, you will note that I didn't say put a Diode across the coil. Placing two them as I described shunts the Vcc and the collectors of the drivers to ground, insuring these two nodes never go negative more than Vj of the diodes. Two diodes connected like this will still permit an AC ring voltage across the coil and Piezo.

Hazim, odds are that your drivers went west, not because of spikes though. You said they were running very hot, which is not surprising. We don't know what the DC resistance of your inductor is but my guess is it's a few Ohms or less. This means that the transistors max current and wattage may have been exceeded. Even if collector currents aren't being exceeded, I know (definitely) that the wattage is! Your driving two bases with a 10K resistor. This value is far too high to fully saturate one transistor, no less two, with a load as low in resistance as your coil is. Furthermore, it's doubtful that those transistors are matched and therefore there's no guarantee that they will share the coil current equally. Are you sure that your drivers are wired exactly the way commercial unit is?

#### CDRIVE

Joined Jul 1, 2008
2,219
I did some searching for various Piezo driver circuits and none of the hits used protection diodes. The few piezo drivers that I've built didn't require ear splitting decibel levels, so I used a simple resistor across the piezo, so I never concerned myself about it.

Here's the electrical equivalent of a piezo resonator which, in my mind, explains why protection isn't required.
http://www.efunda.com/materials/piezo/electronics/elec_equiv_circuit.cfm

Here's a transformer coupled driver.
http://www.discovercircuits.com/DJ-Circuits/beeper4.htm

#### Kingsparks

Joined May 17, 2011
118
Kingsparks, you will note that I didn't say put a Diode across the coil. Placing two them as I described shunts the Vcc and the collectors of the drivers to ground, insuring these two nodes never go negative more than Vj of the diodes. Two diodes connected like this will still permit an AC ring voltage across the coil and Piezo.

CDRIVE. My apologies, never meant to say you did, sorry you took it that way.

#### Audioguru

Joined Dec 20, 2007
11,249
The cities in my area put a larvacide in every rain water drain and pond. It doesn't affect animals or people.
Now all the mosquitoes and the bats that eat them are gone.

#### CDRIVE

Joined Jul 1, 2008
2,219
CDRIVE. My apologies, never meant to say you did, sorry you took it that way.
No need for apologies. I didn't take it that way, or any other way. AAC is a technical discussion forum... It's what we do!

Besides, I have been known to be wrong.

#### hazim

Joined Jan 3, 2008
419
Hazim, odds are that your drivers went west, not because of spikes though. You said they were running very hot, which is not surprising. We don't know what the DC resistance of your inductor is but my guess is it's a few Ohms or less. This means that the transistors max current and wattage may have been exceeded. Even if collector currents aren't being exceeded, I know (definitely) that the wattage is! Your driving two bases with a 10K resistor. This value is far too high to fully saturate one transistor, no less two, with a load as low in resistance as your coil is. Furthermore, it's doubtful that those transistors are matched and therefore there's no guarantee that they will share the coil current equally. Are you sure that your drivers are wired exactly the way commercial unit is?
They went hot at higher voltage, 12V and 9V supply but I was using 2N2222, now I'm using SS8050 which have higher Ic, Ic=1.5A, they are matched and share current equally.... In the commercial unit they use SS8050 but in the software that I'd drawn the circuit with there isn't SS8050 this is why I used in the 2N2222 in the circuit. At 12V, I was using 2N2222 and they burned out, these same transistors became hot when I used a new 9V battery, but using SS8050 they didn't.

So the circuit is working fine now using two SS8050 on 9V battery.

Yes the drivers are wired exactly the way commercial unit is.

The DC resistance of the inductor is 1.5Ω only (I measured it now)

for the frequencies, I said before that I didn't build the 555 part of the circuit, but only the 556 one. I used R5=56KΩ instead of 51KΩ. I also used a 15KΩ in series with a 20KΩ potentiometer in place of R6 to be able to vary the frequency widely as this is still an experimental version.

Calculating the frequencies I got:
U1A Output: 573Hz
U1B Output: 18.4KHz < f < 44.7KHz

Duty cycles ≈ 50%

Now, as the source voltage drops the frequency range decreases, why?

Another question, I can't see neither on the oscilloscope nor on my multimeter (it measures frequency) the second (final) output varies/waves/... at the frequency of the first output, why?

Regards,
Hazim