Solar Insect Repellent for Protecting Crops in fields

The post explains a simple to build ultrasonic insect repellent circuit which can be installed in farms and used by the farmers for driving away all sorts of insects, bugs, grasshoppers etc in order to protect the crops from these potentially harmful pests. The idea was requested by Mr. Cia Brisat.

Technical Specifications

I am a farmer, and need a simple repelling device for use in agricultural equipment, so i can reduces insecticide use.

device features;
a. solar powered with rechargeable battery.
b. a multi pulse repeller, keeps changing the ultrasonic pulse it emits. prevent pests from getting used to the sound.
c. effective range: up to 5000sf.
d. ultrasonic frequency: from 13.5khz to 95khz.
e. dual speaker or more.

could you please help me with a circuit diagram?

thank you.
cia brisat

The Design

The proposed solar insect repellent is based on an ultrasonic wave generator circuit which works by influencing the normal behavior of insects, ultimately driving them away from the area.

The device functions by generating a high frequency at ultrasonic level (above 20kHz), with short pulses. The frequency of the pulses range from 5kHz to 40kHz, selected randomly and transmitted in the environment through special piezo transducers or high power tweeter speakers.

Referring to the above diagram, the design depicts an ultrasonic frequency generator circuit which features a random  frequency selector stage. The idea may be understood with the help of the following explanation:

The IC 555 stages on the left and on the right side are both configured as astable multivibrators for generating the respective frequencies across their output pin#3.

How the IC 555 Operates

The left side IC 555 actually generates the ultrasonic pulses whose frequency is determined by the instantaneous high available across one of the associated sequencing pinouts of the IC 4017.

The shifting or sequencing high logic produced across the 10 outputs of the IC 4017 connects the particular resistor in the array such that this resistor allows the calculated amount of voltage to pin#7 of the IC, and becomes responsible for determining a particular ultrasonic frequency for the left IC 555 stage.

Why IC 4017 is Used

This enables the production of a randomly changing ultrasonic output at the pin#3 of the left IC 555. These randomly changing frequency ranges can be appropriately fixed by assigning calculated resistors across the indicated outputs of the IC 4017.

The speed at which the random selection is implemented depends on the frequency of the clocks applied at pin#14 of the IC 4017 via the right side IC 555 astable stage.

This speed can be altered by either changing the pin#7 upper resistor or the value of the 10uF capacitor of the right IC 555.

The 22k pot associated with the left IC 555 is used for adjusting the pulse width of the ultrasonic waves, the best response may be achieved by some experimentation and by some trial and error.

Since the generated ultrasonic waves needs to powerful enough to reach the entire field, the emission impact needs to be extremely powerful.

This is ensured by feeding the pin#3 output from the left IC 555 to the input of a 100 watt amplifier. This amplifier may be built at home by using a suitable circuit design such as a TDA7294 IC or by procuring a readymade unit from the market.

Once all the above procedures are executed, a high power transducer or a tweeter may be connected with the output of the amplifier for initiating the intended ultrasonic insect repelling actions.

An example of a 100 watt tweeter can be witnessed in the following image:

Power Supply Specs for the Circuit

The circuit is specified to work with any voltage within 6 to 15V, therefore a 12V battery becomes just sufficient for powering the entire unit, although for delivering 100 watts, the AH rating of the battery will need to be at least 50 AH.

In order to make the circuit independent of an external power source, a solar panel may be incorporated for charging the specified battery at an optimal rate which could be around 10amps for a 50 AH lead acid battery.

This implies that the solar panel must be rated to produce 20amps at 15V in order to charge the battery,  as well as enable the circuit to be driven in the day time while the battery is also being charged simultaneously.

Using a 10 Amp Battery Charger

A suitable 10 amp solar battery charger circuit for keeping the battery optimally charged may be seen in the following diagram and used accordingly: