Car Parking Sonar

Posted on Jun 2, 2012

Tihs circuit has: automatic switch on on rear gear. led-bargraph display. audible bleep on last led. `good old` design style, no microcontrollers! Based on an ultrasonic amplifier from an article seen on a 1982 magazine, it was once installed on the rear bumper of my Volvo Station Wagon. It served very well for many years. Connecting it to the reverse gear lights, it switches on automatically and shows you the distance to the nearest obstacle (according to his beam) on a led scale. When the last led lights, a buzzer is also activated telling you to stop immediately. It works on the sonar principle, sending an ultrasound burst and listening for first echo.

Car Parking Sonar
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The burst generated by the oscillator built around U4D (you must set the frequency using TR2 to have 40 kHz or the maximum sensitivity), U4E buffers the output and U4F boost the signal doubling the voltage span across the TX piezo transducer . A new burst is generated each time the decade counter (4017 in the circuit diagram) is in its reset state, that is output 0 is selected. The other outputs (1 to 9) are scanned sequentially following burst generation, until an echo strikes back the RX receiver. It is then amplified by the transistor input stage, triggering the monostable built around U4A - U4B. The monostable stops temporarly the scanning, and a led corresponding to the obstacle distance appears as continuously lit. The buzzer bleeps when the first led (minimum distance) il lit. First of all, be careful not to exchange the ultrasonic transmitter with the receiver: they look very similar, and I suggest you to mark them very clearly from the moment you buy them. During setup, place the ultrasonic transducers over a soft surface, near the border of a table, 10 cm apart of each other pointing outwards the table. Then adjust TR1 and TR2 using a rigid surface (for example a metal sheet) placed in front of sensors, at a variable distance. I enjoyed the sonar for many years. It was installed below the car's rear bumper in a plastic case. Do not choose an enclosure too small: always separate the transducers by 7-10 cm and...

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