Shoo Dog !


We’ve all had occasion
to be annoyed at inconsiderate dog owners whose animals relieve
themselves on the private property of others. This problem can hardly be
solved in a lasting manner using verbal (or even physical) means, so
recourse to an electronic remedy is better and friendlier. The starting
point for this circuit is a ready-made passive infrared sensor (PIR), such as can be found in inexpensive movement detectors. The relay contact of the PIR
energizes the power supply of the circuit shown here. The power supply
generates a voltage of around 15 V after rectification by D1-D4 and
filtering by R1/C3 and R2/C2. This voltage powers a square-wave
oscillator comprising IC1a, R3/C1 and IC1b (acting as a buffer). The two
unnecessary gates are simply connected in series with the buffer, so
that they work with defined levels.

Circuit

Circuit diagram

The R-C network is dimensioned such that frequency of oscillation is
greater than 20 kHz. The amplitude can be set using P1. An IC power
amplifier follows the oscillator to amplify this tone to a level that
will be deafening for dogs (and other small creatures). We use the ST
Microelectronics TDA2030 (http://us.st.com/stonline/books/pdf/docs/1458.pdf),
The peripheral circuitry corresponds to the specifications in the data
sheet. With a supply voltage of 15 V, the TDA2030 can generate around 5W
into a 4Ω speaker. According to the data sheet, the supply voltage of
the TDA2030 can be increased to as much as 30 V, at which level it
generates a hefty 16W into 4Ω (or 11W into 8Ω). However, the 4093 still
must be operated at 15V, which is the maximum allowable supply voltage
for a CMOS IC.

In principle, any inexpensive piezoelectric tweeter whose frequency
response extends past 20kHz can be used for the speaker; it should have
the highest possible sound pressure level (>100dB). A suitable type
is listed on page 626 of the Conrad Electronics catalog. The impedance
of such speakers rises to around 40 to 50 Ω at 20 kHz, so it is
naturally not possible to obtain the power listed in the data sheet
using this circuit. Nevertheless, it should be more than enough to scare
off dog and master.


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