The theory of insect repellent circuit is quite complex though it is possible to give a rough outline of what happens.
It seems that mosquitoes and other nasty insects only mate at certain times and except for these times the two sexes are most unfriendly, in fact they stay well away from each other.
It has also been reliably established that it is only the female oi the species that actually bites;
I have never closely examined a bug that has bitten me but I take the word of experts who know about such things!
The third fact that we need to know is that the male mosquito (and this applies to other bugs as well) beats its wings at a slightly different rate than the female this is one way that they identify each other.
Simulating Male Bug Sound
From these gems of information it will be seen that if one electronically simulates the sound of a male mosquito, the females will steer well clear. We are mentioning mosquitoes here but the same factors also apply to other bugs.
It is a very simple matter to simulate the noise of a male mosquito, all that is needed is a simple audio oscillator feeding an earpiece, the frequency has to be adjusted fairly accurately (you don‘t after all want to sound like a female and attract them!) and so a preset control is necessary.
Using Earphone as the Transducer
The sound level required is very low and a small earpiece is quite sufficient. In any case there would be strong dis- advantages in producing the sound too loudly - it may even be more objectionable than the bugs.
The circuit of the proposed insect repellent shown is a simple audio oscillator whose frequency of operation can be varied over a wide range, in fact from about 500Hz to 10KHz and this will take in the range of all the common bugs. The circuit is a straightforward multivibrator with VR1 altering the audio frequency.
This produces a square wave which is applied across the small crystal earpiece connected between the collector of Tr2 and the negative line.
Crystal earpieces have a very high impedance and it will in no way affect the operation of the circuit. Pretty well any transistors can be used in this simple circuit but if PNP types are used the battery supply should be reversed.
Selecting the Right Components
The values of the capacitors are not too critical either and if others are used and it is found that the frequency range is not adequate, R1 can be altered to bring it back to the right sort of range.
The current consumption is low at 2-3mA, this varies slightly with the frequency, but a PP3 battery will last quite a while; after all the unit will have to be left on for long periods.
None of the components need be large and the unit can be built in a small box to fit into a jacket pocket with the components arranged so that the earpiece is external. The preset VR1 should be a small skeleton preset with a facility for adjusting from outside.
As to adjusting for the right frequency this is a matter of trial and error. I have had some success by adjusting the note to that of a bug in the hope that it was male, I must have been lucky for the circuit does seem to work.
I have not yet found out what happens if you try to use the unit during the bug mating season but leave that up to the reader .
- Components List
- R1 = 120K
- R2 = 2k2
- R3 = 4k7
- R4 = 2k2
- C1 = 0.003uF
- C2 = 0.003uF
- VR1 = 100k preset
- TR1, TR2 = 2N2926
- SW1 = SPDT switch
- B1 = PP3 9V battery
- Crystal Earpiece
Another Insect Repellent Circuit
The heading about insect repellent circuit may possibly in the beginning belong a lot more in the pages of a biology or a chemistry book, however we are not really kidding.
You can actually try to make life unpleasant beyond doubt with kinds of bugs using electronics.
The concept is pretty difficult even though you are able to provide a tough description of what comes about. It would appear that mosquitoes only mate at peak times and apart from these times both sexes are usually most unfriendly, the truth is they reside very well far from one another.
They have also been dependably founded that it must be simply the female of the species that really bites.
The third proven fact that we have to find out could be that the male mosquito (and this also is applicable to other bugs also) beats its wings at a somewhat different rate compared to female this can be one of the ways which they recognize one another.
Through these gems of knowledge it will likely be observed that when one electronically resembles the noise of a male mosquito, the females will certainly steer well clear.
We have been talking about mosquitoes in this article however the similar aspects furthermore employ for some other bugs.
The insect repellent circuit demonstrated above is an easy audio oscillator whose frequency of operation could be varied over a wide range, in reality via around 500Hz to 10kHz and this will require within the range of all the typical insects.
The circuit is an easy multivibrator using RV1 modifying the audio frequency. This constitutes a square wave which can be employed along the small crystal earpiece linked amongst the collector of Q2 and the negative line.
Crystal earpieces possess a higher impedance and it will hardly impact the functioning of the insect repellent circuit.
Fairly good any kind of transistors works extremely well within this easy circuit however PNP sorts are employed, the battery supply needs to be corrected.
The values of the capacitors aren't too essential either and if others are used which is identified that this frequency range is not really sufficient, R1 could be modified to deliver it back to the right sort of range.
The current usage is minimal at 2-3mA. This can vary somewhat using the frequency, but a 9V transistor battery can last a long time; in the end the unit must be left on for very long periods.
Probably none of the elements required large and the unit could be constructed in a small box to install into a jacket pocket using the components outlined in order that the earpiece is external.
The preset RV1 can be quite a small skeleton preset along with a feature for modifying from outside. As to fine-tuning for the right frequency this can be a matter of learning from mistakes.