i need info about obstacle detection

i actually want to use the ultrasonic sound waves to detect obstacles at a range of 30cm , i have no idea how to make the circuit and i havent found suitable circuits on the internet :cry: could any one give me an idea to start!!

Here is an idea and something I have been doing. Depending if your application is for your use alone, then you would not mind the "looks" of it so much.

If you get an old Polaroid Camera with auto-focus, you can use the ultasound sensor that comes in it. I have got from used stores cameras for like U$3 to $5. And make some mods, to have it working just fine.
Here is a good link for this:

You can always buy the SRF04 for U$34.50
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Or the Polaroid Ranger for U$57
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