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hi everybody excuse me Ihave a project about ultrasonic for measurment of distance beetween two cars! its not for avoidance of hit!it for reducing the speed to keep the standard distance between two car somy need is about 30 or 40 meters its very long distance but its two neccessary for me how can I do it I read somthing about horn but its .... you know its in a car! what a horn can be our what a car???? accept my special thanks for your helps

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We did this by useing an Israely IR laser with 10 cm reolution, and a serial RS232 output. We implemented a nice car following experiment with that. (and no, I am not allowed to tell more about it :) :) )

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Put a red laser on a stepper motor so it will rotate left and right. Put this near the right headlight. Put a receiver near the left headlight. Park the car with the laser X feet behind another car. Turn on the laser, step the laser to the left until the reflection hits the receiver. The number steps gives an angle, and the distance between the laser and receiver is known. Should be able to calc distance X.

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sorry may be it's the second choice but my final project is about ultrasonic amplifying to 50 meter!

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Hi, Erfan. The basic principle of ultrasonics is sending out a brief sound, then measuring the time until first echo. Using some quick math (sound travels about 150 microseconds per inch), you can determine the distance of the object that caused the echo.

Simple, and you probably know this. But there's another basic physical fact -- the inverse square law also applies to acoustics. That means you're going to need an awfully loud ultrasonic chirp (more like the chirp of the largest pterodactyl that ever lived) to get a reasonable echo at 80 meters total. Hence the horn, I guess.

In additioon, your sound is going to have to be filtered from the noise of air rushing past the transducer (both cars are moving at a reasonable speed).

I'd guess the best advice someone could give you would be to focus on another method of determining distance.

Good luck Chris

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Does it HAVE to be ultrasonic? Those 3.5" tweeters can take about 25V RMS and probably have peak acoustic output at about 3.5KHz... but if you just beeped it for 10ms every 100ms it might not be too annoying. At least if you can hear it, you can test it with a regular microphone.

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