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# Need help with designing a mosquito repeller circuit

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#### denian

##### Newbie level 5
the circuit not working

im trying to build this mosquito repeller circuit, but i can't seem to make it work.

first, i don't hear any sound
second, when i measure the current that flow through the piezo, it is extremely small. only 0.20mA.

pls tell me anything i can change to the circuit to make it work. your help is much appreciated.

the circuit not working

Hi Denian,
Circuit is a simple astable multivibrator.
Piezocrystal is used as a capacitor in the circuit.

1. first 0.2mA current is not small.
0.2m x 10 k ohms is 2V means 1V drop across Vce
2.Check for the oscillator waveform by simply replacing your capacitor with 103 capacitor.
If it oscillates it means you have change the peizo.
3.Any way the oscillator time period is of the order
of 10K ohms x 10 nF = 100 us= 0.1ms
So 555 timer will easily do your job connect the peizo to the output of 555 timer

Lim Chen San

### Lim Chen San

Points: 2
the circuit not working

Hey Denian!
First of all make sure that your piezo has no internal oscillator. Only then you need to give external oscillations else dc would be enough.
Check out this link as well
https://www.flashwebhost.com/circuit/mosquito.php

Hope it helps!

Giri

the circuit not working

you have gotten some good advice so far. I wonder if the piezo is resonant at the frequency you want. If you have an o'scope you would know.

I got currious about this circuit - I've not seen multivibrators for high frequency (10K) applications before so put it on a simulator (switcherCAD). It does not oscillate with a 103 cap for the piezo. I am not sure what the problem is. I can get it to oscillate at a much lower frequency (50 hz or so) by fiddling with the resistors and caps. I'm not sure the simulator is handling it correctly as I get some rather odd results with the values from your circuit.

I agree that a 555 would be good way to drive the piezo. I KNOW that can be made to oscillate at 10kHz.

Phil

Re: the circuit not working

philba said:
you have gotten some good advice so far. I wonder if the piezo is resonant at the frequency you want. If you have an o'scope you would know.

I got currious about this circuit - I've not seen multivibrators for high frequency (10K) applications before so put it on a simulator (switcherCAD). It does not oscillate with a 103 cap for the piezo. I am not sure what the problem is. I can get it to oscillate at a much lower frequency (50 hz or so) by fiddling with the resistors and caps. I'm not sure the simulator is handling it correctly as I get some rather odd results with the values from your circuit.

I agree that a 555 would be good way to drive the piezo. I KNOW that can be made to oscillate at 10kHz.

Phil
Phil, symmetrical astable multivibrators will generally not start in swCAD because both transistors are saturated in the DC operating point solution, which it does first. Try naming a node (a base is good) and setting a .ic v(b)=0. This will force one of the transistors off at the start of the sim.

Ron (he of "Chris, you always cease to amaze me" fame).

Re: the circuit not working

hi ron, 'tis a small world but least here there don't seem to be any social deviants.

thanks for the tip. like I said, the results looked wrong.

Re: the circuit not working

Hi denia,
I think the base resistors are too small that the transistors are not biased properly. Try to increase them to make the base current about 1~2 uA.

Re: the circuit not working

vale said:
Hi denia,
I think the base resistors are too small that the transistors are not biased properly. Try to increase them to make the base current about 1~2 uA.

tried it. still can't work.

one question, how do i know whether the piezo has internal oscillator or not?

the circuit not working

I dont know what those mosquitos are afraid of and even the working freq of circuit (suppose somewhere in high audio freq ), but c2 seems to me very low . Try to increase it starting from 1 nano till you get success . If not , post here .

P.S Dont you think you will be unconfortable with this sound before mosquitos fly away ?)

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