The device contains two oscillator is enabled by a signal successively. The first of them assembled on the logical elements of DD1.1-DD1.3 (see the scheme in Fig. 1). It generates rectangular pulses with a duration of high level of 0.45 s, and low - 0,55 S.
The output signal of this oscillator controls the operation of the second generator, performed on the elements of DD1.4 - DD1.6. At a high level at the output of the first the second generator is inhibited, while changing levels of the second generator starts forming a sequence of rectangular pulses with a frequency of about 400 Hz.
Transistor VT1 assembled the current amplifier loaded by a dynamic head BF1.
In the vehicle the device is connected in parallel to the lamp, signaling reverse gear. Immediately after power-on the detector begins to play the sound pulses.
All the parts except the speaker drivers are mounted on a printed circuit Board from foiled fiberglass with a thickness of 1 mm the Drawing Board shown in Fig. 2. She, along with the head placed in a sturdy metal or plastic box, mounted in the trunk of a car.
Ready is desirable to cover cost with a waterproof varnish - this will reduce the dependence of the motion detector function from dust and moisture.
Author: I. Zabelin, Moscow