Mosquito Repeller

Thread Starter

iliev986

Joined Oct 29, 2020
19
Repeller.PNG
Hello,
This should be a multivibrator circuit that I tried to download directly from a PCB board (it is very likely to have been downloaded incorrectly ). The reason i think so is that in transient mode there are no generated impulses-only constant value of DC voltage is displayed on the output of the electrical circuit, which is the collector ot the NPN transistor. On the load,there must be a piezoelectric crystal, but since I'm just testing whether it will switch the output, I haven't put a similar one. Also I am asking myself why is there a positive voltage of 700 mV at the base of the PNP transistor (where does it come from?) and a next question follows: from where the capacitor gets these 700 mV, i mean how does it charge, and discharge? This capacitor cannot form a positive feedback to switch these two transistors. I can also add that the PNP transistor cannot turn on with positive voltage..i am so confused :(
 

Thread Starter

iliev986

Joined Oct 29, 2020
19
hi 986,
Welcome to AAC.
The PNP Emitter Base is forward biased, current flows thru E > B junction to 0V via 82K
E
I guess it's just that the circuit connects differently to work as a generator, because apparently it works now, but it's just like a simple circuit with a "learning purpose" . I think this is an astable multivibrator,but i dont know how to connect it properly. I also guess I will need a larger value for the capacitor.
 

Hymie

Joined Mar 30, 2018
991
There have been a number of studies showing that these supposed mosquito repellers (using a high frequency sound) have no beneficial effects (they do not discourage mosquitoes from biting you).

If you live in or are planning to visit a known malaria area (or where other disease is spread by mosquitoes), then you should take appropriate precautions to minimise being bitten (including the use of spray, covering up, using a mosquito net etc.).
 

Dodgydave

Joined Jun 22, 2012
10,050
I used to holiday in Gambia, and it's rife with mossy's, and I made a repellent using a 40Hz frequency which imitates the dragonfly , which is the Enemy of the Mossy, and to my surprise it worked, downside is you here the low humming noise at night, unless you're hearing is poor .
 

Thread Starter

iliev986

Joined Oct 29, 2020
19
There have been a number of studies showing that these supposed mosquito repellers (using a high frequency sound) have no beneficial effects (they do not discourage mosquitoes from biting you).

If you live in or are planning to visit a known malaria area (or where other disease is spread by mosquitoes), then you should take appropriate precautions to minimise being bitten (including the use of spray, covering up, using a mosquito net etc.).
I had read that once female mosquitoes reproduced, their hearing threshold drops, so it is recommended that these generators run at a lower frequency. But otherwise, taking precautions is also a very important factor!
 
This popular two-transistor oscillator circuit is missing a resistor or two. It needs one to limit base-drive (between the two transistors; C of NPN to B of PNP) to prevent damaging them, and a second across the NPN E-B junction for speed.
Mosquito repellers are ultrasonic, as I remember building them in the 1970's using a unijunction transistor with crystal earplug/headphone. Not 40Hz.
 

Audioguru again

Joined Oct 21, 2019
3,505
Why don't simulators like LTspice read the datasheet? It can severely overload a transistor with a massive current but the circuit works fine in simulation but would probably be destroyed in a real circuit.
 

WBahn

Joined Mar 31, 2012
26,398
Why don't simulators like LTspice read the datasheet? It can severely overload a transistor with a massive current but the circuit works fine in simulation but would probably be destroyed in a real circuit.
Because simulators can't read.

I understand what you are complaining about, but trying to incorporate limiting behaviors like this in every component model would bring the simulator to its knees very quickly. Furthermore, to properly utilize much of the information would require additional information, such as heat sinking or thermal coupling, that the person writing the schematic would have to supply on an instance-by-instance basis.

This is one of the reasons why simulation results need to be reviewed with an eye toward applicable real life issues. The simulation usually can be made to look at parameters that are of particular concern and produce some kind of flag if something is amiss.

I remember when IC models made no effort to accurately model power consumption; they only cared about I/O pin behavior. So it was not uncommon at all to get a model for a particular opamp and get your circuit working in simulation just the way you wanted it to and then measure the power supply pin only to discover that it was drawing kiloamps or more. The games they played to get the model to simulate fast enough to be useful while being reasonable faithful to the I/O characteristics precluded faithful power behavior. Now computers are fast enough to deal with higher fidelity models, so most newer device models do a pretty good job of modeling power behavior.

Another issue is what should the simulator do if your 1/4 W resistor is dissipating 1 kW? How should that information be conveyed? Unless the simulation itself crashes, the sad reality is that most people will just ignore it.
 

Thread Starter

iliev986

Joined Oct 29, 2020
19
Because simulators can't read.

I understand what you are complaining about, but trying to incorporate limiting behaviors like this in every component model would bring the simulator to its knees very quickly. Furthermore, to properly utilize much of the information would require additional information, such as heat sinking or thermal coupling, that the person writing the schematic would have to supply on an instance-by-instance basis.

This is one of the reasons why simulation results need to be reviewed with an eye toward applicable real life issues. The simulation usually can be made to look at parameters that are of particular concern and produce some kind of flag if something is amiss.

I remember when IC models made no effort to accurately model power consumption; they only cared about I/O pin behavior. So it was not uncommon at all to get a model for a particular opamp and get your circuit working in simulation just the way you wanted it to and then measure the power supply pin only to discover that it was drawing kiloamps or more. The games they played to get the model to simulate fast enough to be useful while being reasonable faithful to the I/O characteristics precluded faithful power behavior. Now computers are fast enough to deal with higher fidelity models, so most newer device models do a pretty good job of modeling power behavior.

Another issue is what should the simulator do if your 1/4 W resistor is dissipating 1 kW? How should that information be conveyed? Unless the simulation itself crashes, the sad reality is that most people will just ignore it.
The simulation program that I use (EveryCirciut) is relatively good, compared to the previous software products that have been offered to me and that I have worked with. Especially for this type of circuits and after spending hours on something "simple" (because I thought the circuit didn't work) I realized that the program itself reacts differently when it comes to generators that dont involve IC's. There is no way to set a simulation of time analysis in it, unless a source with a certain period of signal repeatability is set in order to achieve some modulation. Indeed, it is much more convenient for the program itself to set values of the basic parameters of the passive and active elements than to work with a database, which must be set to the respective element each time.
 
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