54 Robotics: Sonar Sensors
Description
This article is from the Robotics FAQ, by Kevin Dowling nivek@cs.cmu.edu with numerous contributions by others.
54 Robotics: Sonar Sensors
The time it takes for an acoustic pulse to propagate through air or
water, reflect from the environment and return to a detector is
porportional to the distance.
Acoustic time-of-flight devices have been around for awhile now. The
ubiquitous Polaroid device is cheap and easily integrated and has has
found wide use in robotic devices. Other companies have developed nice
complete turnkey sonar devices though and Polaroid is no longer the
only choice.
"Polaroid Corporation "
119 Windsor St,
Cambridge, MA 02139
tel: 617.386.3961
fax: 617.386.3966
tel: 800.225.1000 ordering
tel: 800.225.1618 technical assistance
Polaroid Ultrasonic Components Group offers two ultrasonic ranging
kits:
Specs:
Distance range: 0.26 to 10.7 meters
Resolution: Nominal +- 3mm to 3m, +-1% over entire range
Sonar acceptance angle: approx. 20 degrees
Power Requirement: 6VDC, 2.5 Amps (1 ms pulse), 150mA quiescent
Weight: Transducer, 8.2gm, Ranging module, 18.4 gm
Designer's Kit:
1 transducer, 1 ranging module, electronics display accurate to
1/10th meter. Cost is $169
OEM kit:
2 transducers, 2 ranging modules. $99.
Piezotransducer kit
2.5cm-1500cm +/- 1%, RS-232 port and analog output, extra real
estate, $299
Polaroid has several new products as well: K-series piezo transducers
and 9000 Series Environmental Transducer.
Modifying the drive circuitry:
This section describes a simple addition to the drive circuitry, the
Polaroid ranging system can detect objects as close as 10cm.
The board has two extra signals: BLNK and BINH. Asserting BLNK
(driving it HIGH) resets the ECHO RS-latch, and asserting BINH
shortens the internal blanking interval (which is 2.38 ms by default).
Thus, the solution would seem to lie in asserting BINH after a
reasonable amount of time (less than 2.38 ms after asserting INIT) to
detect objects closer than 1.3 feet. This doesn't work very well
because BINH is very susceptable to noise, and attaching a driver to
it wreaks havoc possibly because of the anomalous current sink during
the transmit phase. This can be fixed by asserting BLNK during the
blanking period (ie the new blanking period) while negating BINH and
asserting BIHN after the blanking period while negating BLNK. This can
be done easily with a one-shot or some other timing device (eg
computer timer, etc).
A computer timer can be used. The timer goes HIGH tblank ms after INIT
is asserted, where tblank=0.15*dist and dist is the threshold distance
in inches). The timer output goes to BINH and the inverted timer
output goes to BLNK. The timer output should be inverted with an
LS/TTL inverter to delay the negation of BLNK, otherwise the RS latch
may do weird things. [From Richard LeGrand]
"Siemans"
Nice complete sensor package, 5 degree cone angle
"Massa "
Components
"Texas Instruments "
At one point TI made a Type SN28827 Sonar Ranging Module. See TI
Applications Notes D2780. Under $50, needs only 5VDC Not sure if these
units are still manufactured but they are often in surplus catalogs.
However some other products include these: See data sheets at:
[40]http://www.ti.com/sc/docs/psheets/SPECIALF.HTM Data sheets
available in several formats. 1. TL851, SONAR RANGING CONTROL 2.
TL852, SONAR RANGING RECEIVER
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