Birds provide many benefits to our planet's ecosystem. But birds can also cause a lot of harm to the plants that we grow in the garden and fields. This bioacoustic repeller is capable of repelling feathered pests. I used a compilation of recordings of birds of prey sounds, mainly against starlings. The audio recording is recorded on an SD card and repeated at a certain time interval during daylight hours. The device has a built-in lithium-ion battery that can be recharged from a solar panel. You can also supply separate power from external batteries or a power supply with a voltage of 5 to 50 volts. Additionally, you can connect or build in a sound amplifier to the device to impact a larger area.

I came up with and assembled a simple device that will effectively keep birds away. I also developed a photo relay circuit that turns off the repeller at night. Everyone knows that birds roost early and wake up with the first rays of the sun. Exceptions include nocturnal predators. It is the birds of prey that starlings are afraid of, which destroys the harvest.

After a cherry tree appeared on my property, my attitude towards feathered dinosaurs changed radically. Over the course of several years, these winged creatures feasted on the fruits of my labour. Every spring, I watched my early cherry tree as it was purposefully destroyed by flocks of starlings. As a result, every day there were fewer and fewer cherries. This also applies to farmers and agricultural landowners, for whom birds cause many problems.

This device can be used for other purposes as well. For example, you can record an audio recording to scare cats or dogs away. Based on a twilight photo relay, you can assemble a circuit to control lighting or other devices. It is also capable of playing music when the lights are turned on or off. Everything depends on your imagination and specific tasks.

Supplies

Materials:

Electrical box (plastic container) 75×75 mm IP55, 65, & above
Ribbon or elastic band with a key-lock
Optional for the external photosensor: plastic capsule (translucent body)
PET bottle (optional)
Adhesive tape
Heat-shrink tubing
Plastic nylon straps (screeds)

Electronics:

VT1: 2N3906 (bipolar PNP transistor); (BD234, BC307)
VT2: AOD436 (MOSFET N-channel transistor); (IRFZ44N, IRF630/640)
VD1: LED red (640 nm) L-53SRD-E (optional)
PH: SK-KE-10720 (Light Dependent Resistor, 650 nm, 5 mm)
R1: 1k variable resistor
R2: 10 Ω
R3: 10k
R4: 680 (1-1.5k)
MP3 format decoder board module amplifier decoding audio player (FQ#59)
Micro SD card (1-32 GB)
Li-Ion battery 18650, 3.7V, 2000 mAh x 2ps.
Charging/power supply 5V (5–60V), current from 1A & above
solar panel 5–18V current from 250 mA and above (1A)
speaker or horn: 4 Ohm/3–10 Watt
DC-DC Adjustable Step Down Buck Converter Power Module 4.5-50V to 3-35V/2A:LM2596HVS/LM2596HV (or XL4015E1)
lithium-ion battery charging board with protection Type-C/Micro/Mini USB 5V 1A: TP4056
DC Connector 5.5×2.1/2.5 mm 3.5×1.3 mm DC Power Plug Female Jack Socket
(optional) Audio Amplifier Board Module TDA2030A 6-12V
electrical wires and connectors
and other consumables (thermal shrinkage, etc.).

Tools:

Drill machine & drill d = 4-6 mm
soldering iron and consumables
Hot glue gun & glue
assembly knife
Multimeter
(optional) heat gun (building hair dryer)
(optional) electric burner
Wire cutters, screwdrivers, scissors, tape measures, markers, and other tools.

The minimum set of parts in this circuit makes it simpler and more reliable, and it also allows you to solder all components with a simple hinged installation. These radio components can be found on old circuit boards from computers and other electronics. And the MP3 player can be replaced with another storage medium, say an old phone, by adding a small standard amplifier (TDA2030) that can be connected to the phone's speaker output.

Step 1: How Does It Work?

Initially, I connected the repeller via a simple MP3 player. The device plays an audio recording in advance on the SD card within a few minutes and repeats it every hour. I also used a photo relay that turns on the ripper throughout the day. At night, the device does not operate and thus does not disturb neighbours. Solar energy powers the device. A small solar panel paired with two batteries does the job quite well. In cases of cloudy weather, the battery will have to be additionally charged from a charger or powered from an external source. The repeller can be switched on separately using a switch located on the body. The solar panel produces electricity with a maximum voltage of approximately 18 volts. To step down, I used a DC-DC step-down converter. The converter can accept voltage from 5 to 50 volts at the input and output 5 volts to power the device. The 5-volt output power is connected to the battery charging board. It supplies power to the MP3 player and connects the battery separately. The charge management board (BMS) also protects the 3.7 V lithium-ion battery from being discharged and overcharged. The battery is connected, through a switch, to a photo relay, which controls the inclusion of the MP3 player board. An external speaker is connected to the audio output of the device. You can use a speaker, such as a siren or speaker. The MP3 player produces approximately 3 watts of audio output power. For more power, you need to additionally install an internal or external audio amplifier.

Step 2: Twilight Photo Relay & Electrical Scheme

In the circuit I developed, the light sensor is a photo resistor PH, which, together with the trimming resistor R1, forms a voltage divider. This allows you to change the level of the controlled voltage at the base of the transistor VT1. As soon as the light level increases, the decrease in the resistance of the photo resistor provides enough voltage to turn on the PNP transistor. It is no coincidence that this type of transistor is used; it opens with a negative voltage. If you use a transistor with a NPN junction structure, the circuit will work in reverse. That is, the transistor will open at dusk to allow the device to operate at night. This circuitry can be used if you need to turn on, for example, an LED lamp. Turn it on when the level of natural light decreases.

Next, the opening of the transistor VT1 causes a change in the threshold of the gate VT2. By using a MOSFET N-channel field-effect transistor to connect the load, the effect of hysteresis is reduced. The properties of a field-effect transistor to open with a small electric field are ideal for its operation as a key transistor. In the harness of this key, I installed a standard protective resistance R2 at 10 ohms, as well as a resistance R3 at 10 k.

The voltage divider created on resistors R2 and R3 can regulate the control voltage between the drain and source to turn on the field-effect transistor VT2. To indicate the operation of the photo sensor, you can install a VD1 LED with a limiting resistor R4 between the emitter and the power supply ground. Thus, when transistor VT1 opens, a current passes between the emitter and collector, which powers this circuit. If this light indication is not needed, then it can be excluded. The MP3 player is connected as a load in this circuit.

When the field-effect transistor is triggered, a current passes between the drain and source, which powers the load. The MP3 player runs on one lithium battery. A voltage of 3.7–4.2 volts is quite enough for the operation of this circuit, and it also simplifies the design as a whole.

Step 3: MOSFET Transistor

I want to talk about the use of a field-effect transistor as a key in this circuit. I used a small-sized TO 252 transistor, which I found in old computer motherboards. Usually, low-voltage radio-electronic components with a switching threshold of about 4 volts are used. If you use other field-effect transistors, you must take into account their operating voltage.

MOSFET transistors (metal-oxide-semiconductor field-effect transistors) have great advantages in such circuits:

They use minimal power management and have high current gain. Also, it is resistant to large voltage surges. In key mode, they have a faster switching speed. Thus, in this circuit, the use of a field-effect transistor simplified the circuit design of its connection and reduced the level of hysteresis during its operation. Initially, I set the task of creating the simplest possible photorelay circuit to control bioacoustic bird scaring.

AOD436_AlphaOmegaSemiconductors.pdf
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Step 4: Solar Panel and Power Supply

As an additional power supply, a 1-2A pulse power supply with an output voltage of 5 volts to 50 volts can be applied. But since this device is autonomous, I used two 3.7V/2A lithium-ion batteries. It is also possible to provide an external power supply by applying car batteries. The most welcome is to provide an autonomous power source that can be recharged from the sun. I used a small 12–18V solar panel, but enough to recharge the device's battery. To correct the voltage, I applied a DC-DC Adjustable Step Down Converter from 4.5–50V to 3-35V/2A (LM2596HVS). But a converter with a lower output voltage, for example, the XL4015E1, would also be sufficient. Since the battery charging current does not exceed 1 ampere, it is better to use a small converter. That's an output voltage that can be adjusted within 5 volts using the on-board potentiometer. For additional recharging, I applied a standard TP4056 Lithium-Ion battery charge and control (BMS) board. For such devices that are meant to be operated in an external environment, the most recommended is a solar battery.

Step 5: Test & Experimentation

Before the final solution that you see in the photo on the cover, I tested and experimented with this device for three years during the spring-summer period. Initially, I used a simple MP3 player, which I placed in a plastic box. For the photorelay sensor, I used a semi-transparent plastic capsule so that the external light reaches the photoresistor. Rather, the need to protect my garden made me assemble and improvise in the shortest time possible. Thanks to field experiments, I was able to perfect the device to be as effective as possible against birds. Thus, the tests showed that the diffuser can be placed at a distance of about 20–30 m from the fruit trees. Also, the connection of the device must be adjusted depending on the duration of daylight. Sound power depends on the need and coverage area of the land to be protected. Which means that additionally, a higher power amplifier could be applied. But for a field of 10–20 acres, the internal amplifier is sufficient.

Step 6: Audio Recording & Speaker

I searched for a long time for an audio recording of birds of prey and eventually settled on the predators that starlings are afraid of. You can choose other sounds and varieties of birds of prey to suit your needs. The audio recording is played at intervals of approximately 10 minutes for 1 hour, after which everything starts all over again. If anyone requires an hour-long audio recording to scare off starlings, please write to me.

For this device, you can use speakers that match the device parameters: 4 ohms to 10 watts. Initially, for experiments, I used a Bose speaker. But for the external environment, it is better to pick a diffuser with a horn, for example, from a megaphone or siren. I used a horn-shaped speaker.

To make the speaker sound louder, I added a horn made from a plastic bottle to it. In order for it to fit tightly to the base of the speaker, you need to warm it up a little over a fire or use a hair dryer. All this is secured to the base using tape or glue. On the reverse side, it is also advisable to isolate the speaker from exposure to weather conditions.

Step 7: Assembly and Adjustment

In the photos, you can see the assembly process of the bioacoustic repeller. Assembling and installing the components is not difficult to repeat.

To house the electronic components, I used a suitable-sized electrical enclosure. This case houses two lithium-ion batteries. First, you need to drill a hole for the connectors and switch. In order to widen the hole for the switch, I used an electric burner. I assembled the photo relay using a hinged installation and insulated it with a thermal tube. Separately, the photoresistor is brought out onto the device body by drilling a small hole for it. The photocell must be fixed with hot glue; this will prevent water from penetrating into the device. I installed the battery charging board using a hot glue gun. Having previously made an opening for micro USB, all other electronic modules are installed in the device body and, if necessary, glued with hot-melt adhesive. All wire connections must be insulated with a thermal tube. You can also use electrical tape or tape to better insulate the modules.

Setting up the device comes down to adjusting the substring resistor R1 in the photo relay circuit. You need to find such a position for the substring resistor so that the photo relay turns on at dawn and turns off at sunset (about 8–9 PM). I set the trimmer resistor to about 2 kOhm. On this device, the recording is played back from morning to evening, that is, during daylight hours.

The potentiometer can also be mounted on the body of the device by drilling a separate hole for this purpose.

Step 8: External Fixing

If you place the installation in an open field, you need to take care that the speaker should be installed at a height of about 2–3 m or higher. It could be a tree, a mast, or a wall. You also need to take care of the tightness of the device case. The speaker or horn must be installed so that water does not get into it and condensation does not accumulate. When installing the speaker, its directionality is taken into account!

Step 9: Conclusion

During the testing process, the device confirmed my hopes and proved its effectiveness against birds. Within about one week, I got rid of the starlings that were eating the cherries. After this biotherapy, the birds avoided my area and no longer nest on my property.I think that the radius of my device is approximately 0.3–0.5 hectares. If you need to protect a large area, for example, several hectares (up to 5), for example, by planting watermelons, then you need to add another amplifier to this installation and, accordingly, a larger speaker.The acoustic bird repeller that I created can be effectively used against birds such as starlings, blackbirds, rooks, crows, jackdaws, magpies, and seagulls.For greater impact on birds, you can additionally use models or images of birds of prey. For example, such combinations of visual symbols have been used at airports for a long time. From my own experience, I have become convinced that even just an acoustic repeller can save you from birds eating your crops!