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.
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).
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).
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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