234 lines
14 KiB
Plaintext
234 lines
14 KiB
Plaintext
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ÜÜÜÜÜÜÜÜÜÜÜÜÜ ÜÜÜ ÜÜÜÜ
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ÜÛÛÛÛÛÛÛÛßÛßßßßßÛÛÜ ÜÜßßßßÜÜÜÜ ÜÛÜ ÜÛÛÛÛÛÛÛÛÜÜÜÜÜÛßß ßÛÛ
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ßÛÛÛÛÛÛÛÛÛÛÛÛÛÛÜ ßÛÛ ÜÛÛÛÜÛÛÜÜÜ ßÛÛÛÛÜ ßÛÛÛÛÛÛÛÜÛÛÜÜÜÛÛÝ Ûß
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ßßßÛÛÛÛÛÛÛÛÛÛÜ ÞÝ ÛÛÛÛÛÛÛÛÛÛÛßßÛÜÞÛÛÛ ÛÛÛÛÛÜ ßßÛÛÛÞß
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Mo.iMP ÜÛÛÜ ßÛÛÛÛÛÛÛÝÛ ÞÛÛÛÛÛÛÛÛÛ ÞÛÛÛÛ ÞÛÛÛÛÛÝ ßÛß
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ÜÛÛÛÛÛÛÛ ÛÛÛÛÛÛÛÛÝ ÞÛÛÛÛÛÛÛÛÝ ÛÛÛ ÛÛÛÛÛÛ
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ÜÛÛÛÛÛÛÛÝ ÞÛÛÛÛÛÛÛÛ ÞÛÛÛÛÛÛÛÛ ß ÞÛÛÛÛÛÛÜ ÜÛ
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ÜÛÛÛÛÛÛÛÝ ÛÛÛÛÛÛÛÛ ÛÛÛÛÛÛÛÛÝ ÞÞÛÛÛÛÛÛÛÛÛß
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ÜÛßÛÛÛÛÛÛ ÜÜ ÛÛÛÛÛÛÛÛÝ ÛÛÞÛÛÛÛÛÝ ÞÛÛÛÛÛÛßß
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ÜÛßÛÛÛÛÛÛÜÛÛÛÛÜÞÛÛÛÛÛÛÛÛ ÞÛ ßÛÛÛÛÛ Ü ÛÝÛÛÛÛÛ Ü
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ÜÛ ÞÛÛÛÛÛÛÛÛÛÛß ÛÛÛÛÛÛÛÛÛ ßÛÜ ßÛÛÛÜÜ ÜÜÛÛÛß ÞÛ ÞÛÛÛÝ ÜÜÛÛ
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ÛÛ ÛÛÛÛÛÛÛÛß ÛÛÛÛÛÛÛÛÛÛÜ ßÛÜ ßßÛÛÛÛÛÛÛÛÛß ÜÜÜß ÛÛÛÛÜÜÜÜÜÜÜÛÛÛÛÛß
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ßÛÜ ÜÛÛÛß ßÛÛÛÛÛÛÛÛÛÛÜ ßßÜÜ ßßÜÛÛßß ßÛÛÜ ßßßÛßÛÛÛÛÛÛÛßß
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ßßßßß ßßÛÛß ßßßßß ßßßßßßßßßßßßß
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ARRoGANT CoURiERS WiTH ESSaYS
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Grade Level: Type of Work Subject/Topic is on:
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[ ]6-8 [ ]Class Notes [Essay on hooking up ]
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[x]9-10 [ ]Cliff Notes [Radar for the Home ]
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[ ]11-12 [x]Essay/Report [PC System ]
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[ ]College [ ]Misc [ ]
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Dizzed: 10/94 # of Words:2119 School: ? State: ?
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ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>Chop Here>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ
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Ultrasonic Radar for a Home PC System
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One of the fastest changing and most expensive fields, is that of
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technology. Our computers, printers, modems, and much more is being
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outdated faster than anything else in the world. Just as we buy a new
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computer that does what we want, the industry comes out with a new option
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on a smaller and better computer. There seems to be so much changing that
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unless we invest our life savings into technology, we are considered
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obsolete like our computers.
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What used to fill an entire room, is so small now that it can be
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swallowed with a glass of milk. A computer used to be a mechanical engine
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that had many moving parts and was very slow. Now computers design
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computers that are tenfold their own power and a tenth the size, with less
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parts and using less power.
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An airport or an army base used to have huge structures that could
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send out signals to find out if any aircraft were approaching. This
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technology is now offered to people who have a computer with microsoft's
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quick basic, or a Macintosh, and space (equivalent to that of a coffee-pot)
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to spare. Ultrasonic radar is now a small component for your computer,
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giving computer operators a chance to see low flying objects, household
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furniture, and even themselves on their PC screen. Just to impress a
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neighbour or friend is reason enough to build your own ultrasonic radar
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station.
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Similar to that of a Polaroid, ultrasonic transducers are used in this
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type of radar. A rangefinder emits a brief pulse of high frequency sound
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that produces an echo when it hits an object. This echo returns to the
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emitter where the time delay is measured and thus the result is displayed.
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The Polaroid rangefinder is composed of two different parts. The transducer
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(Fig. 1) acts as a microphone and a speaker. It emits an ultrasonic pulse
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then waits for the echo to return. The ranging board is the second part
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(Fig. 2). This board provides the high voltages required for the
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transducer, sensitive amplifiers, and control logic. Since R1 is variable
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it controls the sensitivity of the echo detector. A stepper motor rotates
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the transducer to get a 360o field of view. For entire assembly see Figure
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3.
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An Experimenter is hooked up to the ranging board to control the
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ranging board and to measure the round trip time of pulses. It also
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controls the stepper motor and communicates with the control computer. The
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connections between the Experimenter, ranging board, and transducer are
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shown in Figure 4.
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The ranging board's power requirements are usually under a 100 mA, but
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at peak transmission the circuit can draw up to 2 Amps of current. Power
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passes from GND (pin 1) and V+ (pin 9). To avoid malfunction a 300mF or
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greater should be connected between pin 1 and pin 9 (or alternately pin 16
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and pin 5). Another 300mF resistor should be added to the Experimenter end
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of the cable.
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Figure 5 shows the timing diagram of the ranging boards's signals. It
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takes about 360 microseconds to transmit the pulses. The transmitter waits
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1 millisecond for the pulse transmission and transducer to complete it's
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task. Then the experimenter waits for the pulse echo to return. If a pulse
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is detected the board sets ECHO at high. The Experimenter times the
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difference between BINH going high to ECHO going high. The experimenter
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sets INIT to low, waits 0.5 seconds for the echo, if no echo is heard the
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experimenter cancels the measurement.
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The measured time is sent to the computer which then calculates, at
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thousands of calculations per second, the distance based on the speed of
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sound (1100 feet per second). With a program called DISTANCE.BAS the exact
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speed of sound can be calculated according to the local weather conditions.
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The stepper motor is used to rotate the radar so it can scan 360o
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around the room. An ordinary DC motor would not do for such a project. The
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rotation must coincide with the emissions and the receptions of the echoes.
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In a DC motor the armature rotates and the brushes connect successive
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commuter bars to windings to provide the torque. The speed of this motor
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depends heavily on how much load there is and how much voltage is applied.
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A stepper motor has different wires to each winding. By energizing a
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winding the armature rotates slightly, usually a few degrees. By
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sequentially charging one winding after another the armature can rotate
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completely around. By controlling the windings energized, the operator (in
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this case the Experimenter board) can control exactly how many degrees the
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motor turns and at a precisely controlled speed.
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In this case a stepper motor is used because it gives a precise
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motor-shaft location for the Experimenter board to follow. In a DC motor
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the board wouldn't know shaft position and it would not be possible for the
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computer to take the distance readings at evenly spaced intervals. With the
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control of the stepper we can control the number of steps and the step rate
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required between each transmission. The Experimenter will control all this.
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There are many types of stepper motors available. These motors have
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either two coils, three coils, two coils with center taps, or four separate
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coils. These are low-cost, light- duty motors that the Experimenter can
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drive. The Experimenter board can control any stepper motor with drive
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voltages from 4.5 - 36 volts and currents up to one Amp. The Experimenter
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has different hook-ups for different motors. Refer to Table 1 for the
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different connections of the stepper motors.
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While all the stepper motors will operate the radar system, it is
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imperative that the different advantages and disadvantages of each be
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considered. The motor's power consumption, torque, and resolution are all
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factors that must be considered when choosing the appropriate motor. A
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unipolar stepper motor with its common leads connected to the positive
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power supply can be driven in modes 7, 9, 11. In mode 7 (also called the
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one-phase drive) the stepper motor minimizes power consumption, because
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only one coil is activated at any one time. This mode has very little
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torque. Mode 9 (also called the two-phase drive) runs two coils at the same
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time. This provides maximum torque, although the power consumption is
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doubled. Mode 11 (called the half-step drive) uses one coil, then two
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coils, alternating between modes 7 and 9. This doubles the number of steps
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per revolution.
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If a stepper motor of twelve volts or less (indicated on the motor,
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along with maximum current, coil resistance and step angle) is used it is
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possible to run both the stepper and the Experimenter from the same power
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supply. It may be more economical to use a rechargeable power supply as an
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alternative to a small power supply.
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If the ranging board, Experimenter, and stepper are run off the same
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power supply, it is necessary to know that the boards use about 100 mA
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each. If a 9 v, 500 mA supply is used the two boards would use about 200 mA
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combined. The motor thus has 300 mA for it's own power consumption.
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Depending on the stepper it must be calculated how much current is
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available per coil. If we were to use a two coil stepper that would be 150
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mA per coil. At this low current the voltage drop would be about 0.7 volts
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per coil for a total drop of 1.4 volts.
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According to: RSERIES= ESUPPLY - EDROP
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------------------- _ RMOTOR
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ICHOSEN
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The new resistance can be calculated and installed in the wiring grid on
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the Experimenter. In this hypothetical case the resistance value would be
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48 ohms. To be sure of the power rating on the circuit, the equation P =
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I2R should be used and the proper wattage value should be placed on the
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resistors. On the Experimenter power can be drawn from +A drive on driver
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A.
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In building this unit two electrical contacts must be maintained as
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the transducer is turning (Fig. 6). This is done using a brass tube three
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inches long. This tube will provide the ground connection between the
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ranging board and the ultrasonic transducer. One end must be insulted with
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electrical tape and covered with a larger 0.5 inch long brass tube (so the
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two tubes don't touch). A hole drilled in the upper (longer) tube provides
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a space where a wire can be fed through the tube and used as one of the
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leads for the transducer. The other end of this wire must be soldered to
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the small brass ring over the insulation. The other lead of the transducer
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may be connected onto the top of the longer brass tube. The outer ring will
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be the positive (+) lead and the inner will be the negative (-) lead of the
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transducer (which can be connected immediately).
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The longer tube can be glued to the shaft of the motor. A plastic cap
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has been placed on the back of the transducer for appearance in Figure 6.
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Automotive alternator brushes can be used as contact leads for the brass
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tubes. The negative lead (from E2 on the ranging board) must be connected
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with the brush to the upper (inner) brass tube. The positive lead (from E1
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on the ranging board) must be connected to the lower (outer) tube. This
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assembly can be mounted with the aid of two non-conducting blocks (ie.wood
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or rubber).
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To operate this device one company has taken the initiative to create
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software programs for the PC despite there being no ready made radar kit on
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the market today. "Fascinating Electronics" has written a radar control
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program to work with the Experimenter board. The programs are written in
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Quickbasic called EXPER1.EXE, to operate the radar and DISTANCE.BAS to
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measure distances and the speed of sound. If these programs were not
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available, any computer hacker with the knowledge of the Experimenter board
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would be able to write a simple version of such a program in several hours.
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The DISTANCE.BAS program pulses the rangefinder several times per
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second to measure within 0.01-inch resolution over a range of 6 inches to
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thirty five feet. To calibrate the radar system a flat unit like a box can
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be placed at a measured distance and picked up on the radar. When you run
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the program it will report the distance of the box it has measured. If this
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measurement is wrong the program can be calibrated for the weather
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conditions. The program assumes the speed of sound is 1100 feet per second.
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This can be calibrated by pressing "4" to increase the speed by 10 feet per
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second, "3" to increase the speed by 1 foot per second, "2" to decrease the
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speed by 10 feet per second, and "1" to decrease the speed by 1 foot per
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second. This new speed of sound will be incorporated into your results by a
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RADAR.DAT file.
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To achieve color graphical results the computer must have EGA, or VGA
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displays. If the computer only has CGA the results will be in black or
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white (Fig. 7).
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Each rangefinder distance is plotted in real-time. This provides scale
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information with bars of different colors to and lengths drawn along the
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axes. Tens of feet are marked by long green bars; five foot marks are red;
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the one foot marks are shorter green bars; half- foot markers are black
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bars; and green dots indicate quarter-foot measurements. To the left of the
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display, the program reports the range values and the number of scanning
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points in each rotation of the transducer. The distance and bearing are
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updated with each revolution. By pressing "L" the displayed range increases
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(up to 35 feet). By pressing "S" the displayed range decreases (down to 5
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feet). Pressing "M" will result in scan more points per revolution (up to
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the resolution of the stepper motor used). "F" is used to decrease the
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points scanned per revolution.
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With any text file RADAR.DAT can be altered to change the parameters.
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This screen can be printed in the monochrome mode (CGA) as seen in Figure
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7.
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This radar assembly is a very neat project. It can be costly, but for
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the enjoyment and learning experiences it can be an asset. This radar
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assembly will one day come in a package at one tenth the cost of the parts
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(about $250.00 today). Although it's range is restricted, the transducer
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can be changed and amplified to increase to range. This radar assembly can
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open the gates as monitoring equipment and perhaps one day a property
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monitoring alarm system on your own PC at very little cost. This radar
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assembly has a great potential.
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