Every hobby gardener often think some form of bird-scarer (repeller) can be helpful at certain times of the year to protect the crops. Don’t worry — I am not planning to reinvent the traditional scarecrow stuffed with straw, usually found in the middle of a farmer’s field to protect fruits and vegetables.
But then here is an inexpensive circuit which periodically produces a loud creak to scare birds. The design, consumes moderate power, is built around a common integrated circuit and an ordinary electro-acoustic transducer.
The heart of the circuit is a digital counter of the type 4060 (IC1), a so called binary counter with an internal clock oscillator. At first, CT outputs of IC1 are zero and it then runs through all the digital counter values. This happens at a rate set by the RC network (R1-C3-R2) connected to pins 9 to 11. Q7 output (pin 6) of IC1 drives the loud speaker (LS1). For the loud speaker I used an 8-Ohm, mylar-diaphragm version.
Take a note, the part number of driver mosfet T1 (60NF06) is not very critical. The 5mm red eye (LED 1) is used to indicate that the power is switched on and the circuit is running well.
The power supply of the circuit has been kept very simple. The 6V solar panel (SP1) provides a nominal output voltage of 6V. The 6V dc supply voltage available from the solar panel is buffered by the capacitors C1 and C2. The whole circuit can be powered by the solar panel but if the unit is going to be used for night time (not recommended yet) as well it is better to add a powerful rechargeable battery so that it keeps riding on dark shadows. Finally, the push – to – on button switch (S2) allows you to use the bird-repeller as a signalling device. Just push ‘n’ hold the button switch and listen to the sound of electronics.
Lab Note: No matter how closely the poorman’s ‘handed-down’ scarecrow may resemble a figurehead, birds quickly learn that such static structures pose no threat. However, field trials have shown that this circuit is very very effective in my wife’s backyard vegetable garden because we observed repeatedly that most of the feathered-invaders simply flew away when the unit was activated. Thanks to sound energy!
I am not sure, but driving the standard loudpseaker with a 4 Hz square wave may bring up the chances of it being damaged. Although my speaker is still working perfectly, you can try an appropriate electro-acoustic transducer in lieu of the loudpseaker. Another option is to replace the loudpseaker (LS1) with an electro-mechanical sounder. You can use a home-made sounder built around a small dc solenoid and a circular metal plate. You should link the piston of the solenoid to a moving arm (clapper) which rests against the circular metal plate, and sound is generated when clapper hits the metal plate. If you prefer this method, remember to add a 1N4007 diode across (in anti-parallel) the solenoid connected in place of the loudpseaker. Also remove the interconnection between pin 9 of IC1 and the alarm switch (S2), because it is not possible to enable the signalling mode in this setup.
This bird-scarer makes a sound that is audible to the human ear and therefore may cause human disturbance when used in an area of human habitation.