Dogs, mice, bats and other animals can hear sounds with frequencies up to
4O,O0O Hz. There are several kinds of insects that can also hear or reacto
these sounds. The circuit we propose here produces a continuous sound
emission in frequencies above the human limit, or a range between 18,000
and 40,000 Hz. These sounds are called ultrasounds and can be used in
several experimental and practical applications.
The device we describe here can be used to scare dogs and other animals, in
biological experiments, and many other interesting applications.
The recommended piezoelectric transducer has its maximum output power
between 700 and 3,000 Hz, but it also will operate at higher frequencies
emitting less power.
The recommended power supply is four M cells or a 9-volt battery.
Our project runs between approximately 18,000 and 40,000 Hz, but you can
easily alter this range by changing C1, in a range between 470 pF and 0.001
uF. Frequency can be set by P1 in the range determined by C1.
Remember that the 40938 lC will oscillate in frequencies up to 500 kHz.
The complete circuit of the Ultrasonic Generator, using the four gates of a
40938 integrated circuit, is shown in Figute 1.
Components placement on a printed-circuit board is shown in Figurc 2.
The circuit can be housed in a small plastic box and the transducer will be
fixed in the front panel.
Take care with the position of the polarized parts, such as the transistor,
electrolytic capacitor and power supply.
For continuous operation, Q1 should be mounted on a heatsink'
The transformer is not a critical part. Any transformer with a secondary coil
ranging from 100 to 500 mA can be used in this project.
Parts List - Ultrasonic Generator
lC1 - 40938 CMOS Integrated circuit
Ql - 8D135 medium-power NPN silicon transistor
BZ - Piezoelectric transducer
Radio Shack 273-090 or equivalent
Tl - Transformer: primary 1 17 VAC; secondary 6Vx100 mA
R1 - 10,000 ohm, 114W,5% resistor
R2 - 1,000 ohm, 114W,5% resistor
Pl - 100,000 ohm trimmer potentiometer
C1 - 4,700 pF ceramic or metal film capacitor
C2 - 100 uF, 12 \M/DC electrolytic capacitor
S1 - SPST toggle or slide switch
B1 - 6V or 9V - AA cells or batter
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