Project Description

The following product is intended to be a property – or hornc-protection device. It consists of a field of acoustical, ultrasonic, high sound pressure energy that is triggered when unauthorized intrusion is detected.

Detection consists of the following functions:

• A “trip wire” or closed system such as taped glass windows and doors where a break or open triggers the unit. This function is viaJ3.

• A “switch” input where a closure to ground such as a pressure switch, door, or entrance switch triggers the unit. This function is via J2.

• A "■+ level” input where a voltage pulse or level from other detection equipment such as an infrared intrusion, motion, or sound detec­tion system triggers the unit. This function is via JL

Test and Reset buttons enable total system con­trol.

Upon activation via the above, a moderately pow­ered sourcc of acoustical, ultrasonic energy is pro­duced. causing certain adverse effects to the intruder. These may be paranoia, severe headaches, disorienta­tion, nausea, cranial pain, an upset stomach, or just plain irritating discomfort. Most people are affected in one way or the other, with young women unfortu­nately being the most sensitive. External adjustments enable the user to select clearly audible sounds that serve as an alarm, high-frequency energy that pro­duces the physiological effects, or a combination of both.

The sound pressure level is less than 130 db and will not produce permanent damage if exposure is kept to a minimum. Obvious prolonged exposure is not encouraged for these reasons. A rule of thumb is to keep exposure to less than I hour with a frequency less than 20 kHz at a sound pressure of 105 db or over.

The system consists of the central power and con­trol unit that powers up to six remotely located trans­ducers. These are now positioned to take advantage of potential entrance and intrusion areas, considering that each transducer can produce up to 118 db meas­ured at 1 meter. Since the sound pressure level is log­arithmic. an attenuation factor of -3 db must be factored in every time the distance is doubled from one of the transducer stations.

□river Circuit Description

A timer (IC2) is connected as a stable, free-running multivibrator whose frequency is externally con­trolled by pot R9. The trimmer resistor (RIO) selects the range limit of R9. Capacitor C5, along with the resistors, determines the frequency range of the device (see Figure 28-2).

The square wave output of 1C2 is via pin 3 and is connected to metal-oxide-semiconductor fieid effect transistor (MOSFET) Q2.The drain of Q2 is DC biased through Ll. The amplified square waves are fed to the transducer via resonating coil LI and capacitor C8, along with Q spoiling resistors. R13 through R16. Resonating coils (L2A and L2B) are selected to tune out the inherent capacity of the transducer at their upper-frequency limit, usually around 25 kHz. A sinusoidal wave is generated and allows the transducers to operate at a higher peak power level than the equivalent voltage square wave would. Resonant peaking of the voltage is also obtained. These transducers, unlike their electromag­netic counterparts, have a tendency to draw high cur­rent at higher frequencies. This effect is compensated to an extent by power resistors R17A and R17B. Note the wave shapes shown are at a fixed frequency of 20 kHz.

Timer IC1 is similarly connected as a stable, run­ning multivibrator and is used to produce the sweep­ing voltage necessary for modulating the frequency of lC2.The switch section of R2/S2 activates it, and this sweep repetition rate is controlled by the pot sec­tion R2. Resistor R3 limits the lower range of this repetition time. Capacitor C2 sets the sweep time range. Output from IC1 is via pins 6 and 2 where the signal ramp function voltage is resistively coupled to inverter transistor Ql via resistor R4.The output of Ql is fed to pin 5 of 1C2 and provides the modula­tion voltage necessary to generate the sweeping fre­quency action required. Note that this signal is easily
disabled via the switch section of R2/S2.This is a con­venience when initially setting or checking the range of 1C2 as it eliminates the constant varying fre­quency.

Project Description

Figure 28-2 Phaser pain field property guard schematic

Power is supplied to the system via a conventional step-down converter wall transformer,!!, which con­nects to the system via the DC JACK chassis mount connector. Power is controlled by switch SI that is part of the frequency control pot R9. A light-emitting diode (LED) indicator lamp and an associated cur – rent-limit resistor (R11) tell when the system is ener­gized.

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