"Good old" parking sonar
This was one of my first designs: it is an ultrasonic
It works on the sonar principle, sending an ultrasound burst and listening for first echo. 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.
When the monostable expires, scanning is resumed and restarting the send-and-listen sequence. If no echo is received, the scanning never stops and all the leds are slightly lit.
To set up:
Set TR2 for maximum sensitivity
(usually 40 kHz for most commercially available ultrasonic transducer
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.
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 plenty of sound-absorbing material, otherwise the receiver
will reveal the direct sound instead of the reflected one. The same
applies if the sound travels through a rigid fixture, so it is a good
idea to fix them with separated supports.
Here are a few improvements
and tips I received from readers. Add a 470 kiloohm resistor from the
base of Q8 to the negative pole (ground). Use a BC109C for Q8 and Q9
too. Do NOT use BC109B or BC109A transistors: the gain is not enough.
Some readers have reduced the capacitor C12 to 3.3 nF or even 330 pF.
And by the way, yes, the polarity of D3 is correct as shown and the
LEDs have only one resistor because only one LED is active at any time.
Download full schematics below (SONAR_SC.GIF, 18kB)
Don't forget to check the F.A.Q. page for additional information.
You might want to take a look to the original magazine article ("Sperimentare", april '82) that inspired the project, kindly digitized and posted online by PiEffe (look into the "SONAR" folder).
Links from the web:
A modern alternative schematic, microprocessor based (National COP) ultrasonic range finder
An even more modern one, based on Cypress PSoC, parts, with LCD display. By Fabio Piana.
A low power microcontroller
with LED display