All, I have been working on an ultrasonic sensor since 1994. About two years ago I decided to package the sensor for everyone. It is avaible now. Data sheet is avaiable at the web site.
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The MaxSonar-EZ1: is very low cost, uses just one trasnducer, detects to zero (yes even pressing against the front face), detects to 254 inches (6.45 meters), is the smallest size (smallest PCB & includes mounting holes), is the lowest power (just 2 mA typical at 5V), has a controlled narrow long-range beam,
has a very easy user interface including RS232C, pulse width, and analog votlage.
I posted this because this really is a break through product and I would have wanted one in 1997.