Re: ultrasonic update

["Daniel L. MacIsaac" <Dan.MacIsaac@NAU.EDU>]

> At 22:08 10/13/99 -0500, Pete wrote:
> > I just finished the O'scope analysis of the Ultra sonic motion detector
> > this afternoon.
> >
> > Here's what I discovered;
> >
> > The Ultrasonic frequency is 50kHz with a 50% duty cycle.
> > Each query consists of 17 of these pulses  (350 uSec) followed by a
> > listen phase.
> > Depending on the number of queries demanded, 10 per sec, 25/sec, or
> > Paul's 120/sec, the pulse will have from 100 mSec (10 Hz)  to 8.33 mSec
> > to receive the echo.
> > This means at 120 Hz, the maximum distance the pulse can travel and
> > still get back before the next pulse is 1.4 m.
Pete:

Check out
http://www.wirz.com/sonar/
where you can order the transducers and drive electronics, or download a
specsheet for the Polaroid SONAR system.  Most school sonar systems are
relics of the Polaroid OneStep camera focus system, and use a gold-sputtered
kapton membrane with an AL backing plate as a transducer, NOT a piezo-ceramic
device.  Way more details at the above URL, also check out the amateur robot
sites, the Polaroid SOANR system is very popular with those people as well:
http://www.acroname.com/robotics/info/articles/sonar/sonar.html

Incidentally the SONAR blind spot is due to the original camera design; the
camera was never intended to focus closer than 4 ft.  No need for close
ranging.

Good hunting,

Dan M



Dan MacIsaac, Assistant Professor of Physics and Astronomy, Northern AZ Univ
danmac@nau.edu          http://purcell.phy.nau.edu         PHYS-L list owner