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          ARRoGANT                CoURiERS      WiTH     ESSaYS

Grade Level:       Type of Work           Subject/Topic is on:
 [ ]6-8                 [ ]Class Notes    [Essay on hooking up     ]
 [x]9-10                [ ]Cliff Notes    [Radar for the Home      ]
 [ ]11-12               [x]Essay/Report   [PC System               ]
 [ ]College             [ ]Misc           [                        ]

 Dizzed: 10/94  # of Words:2119  School: ?              State: ?
ФФФФФФФФФ>ФФФФФФФФФ>ФФФФФФФФФ>Chop Here>ФФФФФФФФФ>ФФФФФФФФФ>ФФФФФФФФФ>ФФФФФФФФФ
                   Ultrasonic Radar for a Home PC System

     One of the fastest changing and most expensive fields, is that of
technology. Our computers, printers, modems, and much more is being
outdated faster than anything else in the world. Just as we buy a new
computer that does what we want, the industry comes out with a new option
on a smaller and better computer. There seems to be so much changing that
unless we invest our life savings into technology, we are considered
obsolete like our computers.

     What used to fill an entire room, is so small now that it can be
swallowed with a glass of milk. A computer used to be a mechanical engine
that had many moving parts and was very slow. Now computers design
computers that are tenfold their own power and a tenth the size, with less
parts and using less power.

     An airport or an army base used to have huge structures that could
send out signals to find out if any aircraft were approaching. This
technology is now offered to people who have a computer with microsoft's
quick basic, or a Macintosh, and space (equivalent to that of a coffee-pot)
to spare. Ultrasonic radar is now a small component for your computer,
giving computer operators a chance to see low flying objects, household
furniture, and even themselves on their PC screen. Just to impress a
neighbour or friend is reason enough to build your own ultrasonic radar
station.

     Similar to that of a Polaroid, ultrasonic transducers are used in this
type of radar. A rangefinder emits a brief pulse of high frequency sound
that produces an echo when it hits an object. This echo returns to the
emitter where the time delay is measured and thus the result is displayed.
The Polaroid rangefinder is composed of two different parts. The transducer
(Fig. 1) acts as a microphone and a speaker. It emits an ultrasonic pulse
then waits for the echo to return. The ranging board is the second part
(Fig. 2). This board provides the high voltages required for the
transducer, sensitive amplifiers, and control logic. Since R1 is variable
it controls the sensitivity of the echo detector. A stepper motor rotates
the transducer to get a 360o field of view. For entire assembly see Figure
3.

     An Experimenter is hooked up to the ranging board to control the
ranging board and to measure the round trip time of pulses. It also
controls the stepper motor and communicates with the control computer. The
connections between the Experimenter, ranging board, and transducer are
shown in Figure 4.

     The ranging board's power requirements are usually under a 100 mA, but
at peak transmission the circuit can draw up to 2 Amps of current. Power
passes from GND (pin 1) and V+ (pin 9). To avoid malfunction a 300mF or
greater should be connected between pin 1 and pin 9 (or alternately pin 16
and pin 5). Another 300mF resistor should be added to the Experimenter end
of the cable.

     Figure 5 shows the timing diagram of the ranging boards's signals. It
takes about 360 microseconds to transmit the pulses. The transmitter waits
1 millisecond for the pulse transmission and transducer to complete it's
task. Then the experimenter waits for the pulse echo to return. If a pulse
is detected the board sets ECHO at high. The Experimenter times the
difference between BINH going high to ECHO going high. The experimenter
sets INIT to low, waits 0.5 seconds for the echo, if no echo is heard the
experimenter cancels the measurement.

     The measured time is sent to the computer which then calculates, at
thousands of calculations per second, the distance based on the speed of
sound (1100 feet per second). With a program called DISTANCE.BAS the exact
speed of sound can be calculated according to the local weather conditions.

     The stepper motor is used to rotate the radar so it can scan 360o
around the room. An ordinary DC motor would not do for such a project. The
rotation must coincide with the emissions and the receptions of the echoes.
In a DC motor the armature rotates and the brushes connect successive
commuter bars to windings to provide the torque. The speed of this motor
depends heavily on how much load there is and how much voltage is applied.

     A stepper motor has different wires to each winding. By energizing a
winding the armature rotates slightly, usually a few degrees. By
sequentially charging one winding after another the armature can rotate
completely around. By controlling the windings energized, the operator (in
this case the Experimenter board) can control exactly how many degrees the
motor turns and at a precisely controlled speed.

     In this case a stepper motor is used because it gives a precise
motor-shaft location for the Experimenter board to follow. In a DC motor
the board wouldn't know shaft position and it would not be possible for the
computer to take the distance readings at evenly spaced intervals. With the
control of the stepper we can control the number of steps and the step rate
required between each transmission. The Experimenter will control all this.

     There are many types of stepper motors available. These motors have
either two coils, three coils, two coils with center taps, or four separate
coils. These are low-cost, light- duty motors that the Experimenter can
drive. The Experimenter board can control any stepper motor with drive
voltages from 4.5 - 36 volts and currents up to one Amp. The Experimenter
has different hook-ups for different motors. Refer to Table 1 for the
different connections of the stepper motors.

     While all the stepper motors will operate the radar system, it is
imperative that the different advantages and disadvantages of each be
considered. The motor's power consumption, torque, and resolution are all
factors that must be considered when choosing the appropriate motor. A
unipolar stepper motor with its common leads connected to the positive
power supply can be driven in modes 7, 9, 11. In mode 7 (also called the
one-phase drive) the stepper motor minimizes power consumption, because
only one coil is activated at any one time. This mode has very little
torque. Mode 9 (also called the two-phase drive) runs two coils at the same
time. This provides maximum torque, although the power consumption is
doubled. Mode 11 (called the half-step drive) uses one coil, then two
coils, alternating between modes 7 and 9. This doubles the number of steps
per revolution.

     If a stepper motor of twelve volts or less (indicated on the motor,
along with maximum current, coil resistance and step angle) is used it is
possible to run both the stepper and the Experimenter from the same power
supply. It may be more economical to use a rechargeable power supply as an
alternative to a small power supply.

     If the ranging board, Experimenter, and stepper are run off the same
power supply, it is necessary to know that the boards use about 100 mA
each. If a 9 v, 500 mA supply is used the two boards would use about 200 mA
combined. The motor thus has 300 mA for it's own power consumption.
Depending on the stepper it must be calculated how much current is
available per coil. If we were to use a two coil stepper that would be 150
mA per coil. At this low current the voltage drop would be about 0.7 volts
per coil for a total drop of 1.4 volts.

     According to:            RSERIES= ESUPPLY - EDROP
                              ------------------- _ RMOTOR
                                                    ICHOSEN

The new resistance can be calculated and installed in the wiring grid on
the Experimenter. In this hypothetical case the resistance value would be
48 ohms. To be sure of the power rating on the circuit, the equation P =
I2R should be used and the proper wattage value should be placed on the
resistors. On the Experimenter power can be drawn from +A drive on driver
A.

     In building this unit two electrical contacts must be maintained as
the transducer is turning (Fig. 6). This is done using a brass tube three
inches long. This tube will provide the ground connection between the
ranging board and the ultrasonic transducer. One end must be insulted with
electrical tape and covered with a larger 0.5 inch long brass tube (so the
two tubes don't touch). A hole drilled in the upper (longer) tube provides
a space where a wire can be fed through the tube and used as one of the
leads for the transducer. The other end of this wire must be soldered to
the small brass ring over the insulation. The other lead of the transducer
may be connected onto the top of the longer brass tube. The outer ring will
be the positive (+) lead and the inner will be the negative (-) lead of the
transducer (which can be connected immediately).

     The longer tube can be glued to the shaft of the motor. A plastic cap
has been placed on the back of the transducer for appearance in Figure 6.
Automotive alternator brushes can be used as contact leads for the brass
tubes. The negative lead (from E2 on the ranging board) must be connected
with the brush to the upper (inner) brass tube. The positive lead (from E1
on the ranging board) must be connected to the lower (outer) tube. This
assembly can be mounted with the aid of two non-conducting blocks (ie.wood
or rubber).

     To operate this device one company has taken the initiative to create
software programs for the PC despite there being no ready made radar kit on
the market today. "Fascinating Electronics" has written a radar control
program to work with the Experimenter board. The programs are written in
Quickbasic called EXPER1.EXE, to operate the radar and DISTANCE.BAS to
measure distances and the speed of sound. If these programs were not
available, any computer hacker with the knowledge of the Experimenter board
would be able to write a simple version of such a program in several hours.

     The DISTANCE.BAS program pulses the rangefinder several times per
second to measure within 0.01-inch resolution over a range of 6 inches to
thirty five feet. To calibrate the radar system a flat unit like a box can
be placed at a measured distance and picked up on the radar. When you run
the program it will report the distance of the box it has measured. If this
measurement is wrong the program can be calibrated for the weather
conditions. The program assumes the speed of sound is 1100 feet per second.
This can be calibrated by pressing "4" to increase the speed by 10 feet per
second, "3" to increase the speed by 1 foot per second, "2" to decrease the
speed by 10 feet per second, and "1" to decrease the speed by 1 foot per
second. This new speed of sound will be incorporated into your results by a
RADAR.DAT file.

     To achieve color graphical results the computer must have EGA, or VGA
displays. If the computer only has CGA the results will be in black or
white (Fig. 7).

     Each rangefinder distance is plotted in real-time. This provides scale
information with bars of different colors to and lengths drawn along the
axes. Tens of feet are marked by long green bars; five foot marks are red;
the one foot marks are shorter green bars; half- foot markers are black
bars; and green dots indicate quarter-foot measurements. To the left of the
display, the program reports the range values and the number of scanning
points in each rotation of the transducer. The distance and bearing are
updated with each revolution. By pressing "L" the displayed range increases
(up to 35 feet). By pressing "S" the displayed range decreases (down to 5
feet). Pressing "M" will result in scan more points per revolution (up to
the resolution of the stepper motor used). "F" is used to decrease the
points scanned per revolution.

     With any text file RADAR.DAT can be altered to change the parameters.
This screen can be printed in the monochrome mode (CGA) as seen in Figure
7.

     This radar assembly is a very neat project. It can be costly, but for
the enjoyment and learning experiences it can be an asset. This radar
assembly will one day come in a package at one tenth the cost of the parts
(about $250.00 today). Although it's range is restricted, the transducer
can be changed and amplified to increase to range. This radar assembly can
open the gates as monitoring equipment and perhaps one day a property
monitoring alarm system on your own PC at very little cost. This radar
assembly has a great potential.
