Newsgroups: comp.robotics
Path: brunix!sgiblab!swrinde!cs.utexas.edu!uunet!ftpbox!mothost!merlin.dev.cdx.mot.com!sgi.dev.cdx.mot.com!johnb
From: johnb@sgi.dev.cdx.mot.com (John Bottoms)
Subject: Polaroid(tm) Sensor Update
Message-ID: <1993Sep7.164326.23820@merlin.dev.cdx.mot.com>
Sender: news@merlin.dev.cdx.mot.com (Merlin News System)
Nntp-Posting-Host: sgi.dev.cdx.mot.com
Organization: Motorola Codex, Canton, MA
Date: Tue, 7 Sep 1993 16:43:26 GMT
Lines: 48


   Update on Polaroid(tm) Sensors

Here's the latest poop on the used Polaroid Sensors. I now have the
sensors and documentation on the Polaroid Designers Kit which is
very similar to the used boards I have taken out of cameras. The
board is even cut into the same configuration and the silkscreen 
is similar but components may differ by one or two items, caps,
diodes or resistors. The IC's appear to be the same but marked
with an inhouse number which contains part of the commercial
number. There are actually 2 different commercial boards
available, 1) Polaroid 6500 Series Sonar Ranging Module
PID #615077 and 2) SN 28827 Sonar Ranging Module, from the
TI Linear Data Handbook Volume #1(?).

I am in the process of testing the boards and will be sending them
out to people who have ordered them later this week. I'll send you
mail individually when your unit(s) is shipped.

How It Works
------------
There are 2 chips on the board and the sonar unit is attached by
a short piece of coax cable. The chips are a transmitter and a
receiver. The transmitter is activated by a signal that goes high
on the INIT line. It then generates the chirp signal of 16 cycles
of a 49.4 Khz (300V) signal. The output signal is immediately blanked 
for 2.38 ms. (There is a way to detect closer than 2.38ms if desired.)

The receiver then detects the reflected signal and outputs a high on
the ECHO line. which stays there until until the INIT line is driven
low. It is possible to run the board in multiple echo mode by driving
the Blanking line low and then high after the first echo is received.

The board detects distances from 6" to 35'. The speed of sound at 70degF
and typical barometric pressure is 1125'/second. I'll leave it as an
exercise to the student on what the distances are for the various 
echo times. You could probably dream up a quick circuit that would
interface this to a serial or parallel port on a PC.

There is a transformer on the board that transmits the pulse
to the sensor. It should be attached to the Vcc which has a low
impedance (Vcc or a battery) and it may be necessary to decouple the 
IC's so the chirp
drain on Vcc does not interfere with their operations. The board
runs on supply of 4.5 to 6.8 volts. Accuracy is 2% of the reading
at >1'. There is an onboard crystal oscillator running at 420Khz.

-johnbottoms
