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BallBot/Part3

This website contains an archive of files for the Acorn Electron, BBC Micro, Acorn Archimedes, Commodore 16 and Commodore 64 computers, which Dominic Ford has rescued from his private collection of floppy disks and cassettes.

Some of these files were originally commercial releases in the 1980s and 1990s, but they are now widely available online. I assume that copyright over them is no longer being asserted. If you own the copyright and would like files to be removed, please contact me.

Tape/disk: Home » Personal collection » Acorn ADFS disks » Electron » EUG_submission.ADF
Filename: BallBot/Part3
Read OK: ✔
File size: 1DC6 bytes
Load address: 50206576
Exec address: 33747261
Duplicates

There is 1 duplicate copy of this file in the archive:

File contents
Ultrasonic Sonar System

By far the largest area of development in BallBot has been the work in
developing the sonar system which the robot uses to navigate. This sonar
system must be able to determine what objects are present around the
robot, how far away they are, and whether they are interesting or not.

The system essentially consists of two units: a transmitter, which is
essentially a loudspeaker, and a reciever, which is a microphone. Both
have a very fine resonant frequency of 40kHz. The system works as follows:

On a regular basis (eight times a second), BallBot emits a loud ultrasonic
pulse from the loudspeaker. As this pulse moves away at the speed of sound
(330m/s), some of this energy is reflected back at the robot in the form
of echoes. If there is an object such as a tennis ball present, the echoes
are much stronger, as shown by the diagram. These strong echoes are
recieved by very sensative microphones on board the robot. The distance of
the object from the robot can be calculated because we know that the time
taken for the sound wave to travel out to the object and then return back
to BallBot is equal to the time delay between the signal being
transmitted, and its echo being recieved. Therefore the following formula
can be applied:

The type of object present can also be determined. Different objects
produce different amplitudes of echo depending upon their size and how
absorbant they are to sound waves. As soon as the first signal from the
object is recieved, BallBot's computer begins sampling the sound being
recieved. The hardware converts the peaks in amplitude of the ultrasound
being recieved into binary 1s, and the troffs into binary 0s. Thus a form
of code is formed which is passed to the computer's input circuitry. The
computer then processes the binary code to search for patterns, which it
recognises as objects such as tennis balls.

Systems such as this are only effective, however, when the echoes are
being reflected off objects which are thicker than the wavelength of the
waves being transmitted. In our case, this can be found to be
approximately 8mm using the formula V=fl. Therefore some objects such as
the net and the fence surrounding the court may not be reliably detected.
Othere objects such as the balls and players will, however, still be
visable when this is allowed for. The pattern recognition system must,
therefore, be programmed to ignore any traces which are recieved from
these items if reliable consistent results are to be obtained, and the AI
code must be programmed to work without traces from these surfaces. It is
important that such traces are either picked up reliably every time, or
ignored completely. If they are necessary for the efficient running of the
AI, infra-red sensory systems may be added to detect the net, the fence,
and anything else of interest.

The Transmitter

The circuitry for this sonar system is still very much under development.
The transmitting system has now been designed, built and tested, and seems
to be working satisfactoraly. This part of the circuitry takes one output
line from the computer, and transmits 40kHz from the speakers when it is
high, and turns off the speaker when it is low. Essentially it consists of
a wave generator circuit, producing 40kHz sine waves, and a transistor to
switch the output to the speaker on and off. The circuit diagram for this
is shown below:

It is at first surprising that this circuit works. The collector ->
emitter connection of a transistor acts as a diode, and yet the voltage
across this negative in the lower half of the 40kHz sine wave. Therefore
we would expect half-wave rectified output from the speaker. I suspect
that the reason why this circuit works is that induction or resonance in
the transmitter fills in the lower-half of the wave.

Having built this circuit, and shown that it worked by monitoring the
output using a microphone and an oscilloscope, I decided to test the
response rate of the circuit to see how long it took the transmitter to
reach maximum amplitude after the output line from the computer goes high,
switching on the transmitter. By programming the computer to switch the
transmitter on and off at high frequency, and monitoring the sound output
on an oscilloscope, I found that it takes about 1ms to reach maximum
amplitude from the "blip" control signal being sent, and 1ms to return to
complete silence after being turned off. Therefore I decided that the
computer should send the "blip" signal to this circuit for a minimum of
1ms for it to be sure to have the effect of producing a sound of maximal
amplitude, but not too long that the recieved waveforms from different
objects become blurred in any way.

The Reciever

The ultrasonic reciever is rather more complicated than the transmitter,
and work is still at a very early stage. Our first objective was to find
out exactly work kind of signal the ultrasonic microphone produces when
exposed to ultrasound. Using an oscilloscope, I found that the signal
produced is an a.c. signal which oscillates at 40kHz, and has an amplitude
which varies with the intensity of the ultrasound to which it is exposed.
I expected the voltage of this signal to be proportional to the inverse
square of the distance. The sound spreads out from the source in the shape
of a sphere (or part of a sphere). Therefore at any one time the sound
energy is spread over the surface area of a sphere of distance d around
the source, where d is the distance between the source and the
transmitter. This would indicate the following formula:

The data actually collected through tests with the ultrasonic equipment is
shown below:

Both tests strongly suggest that the voltage of the signal from the
microphone is inversely proportional to the distance. Therefore, this
suggests that:

As you can see, the product of the voltage recieved and the distance of
the source from the reciever is constant. This could be very useful.
Graphs for Voltage x Distance should, therefore, be a straight horizontal
line. Such graphs of voltage x distance are plotted below:

So far, all studies have been of a system involving transmission in a
straight line, with the reciever facing the transmitter. In BallBot,
however, the transmitter and the reciever will be together, and facing in
the same direction. Therefore some tests have been performed for the input
recieved when an echo is bounced off a surface. Data for such tests are
shown below:

Once again, it appears that voltage is inversely proportional to distance.
This suggests that surfaces reflect a constant proportion of the sound
energy back at the robot. Once again, the product of distance and voltage
should be a constant value. But because we know that the distance of the
object is proportional to the time taken for the echo to be recieved, we
can convert this to saying that the product of the time elapsed since the
ultrasonic blip was transmitted and the input voltage is a constant value
for particular surfaces. This is more useful than distance with regard to
designing the BallBot hardware. Graphs for voltage x distance for echo
tests are plotted below:

The constant value of the product of voltage and distance can be found for
different surfaces for the given speakers and output amplitude. The unit
of this value is the volt-metre (Vm). Work is currently in progress to try
to find actual values of this for the kind of objects which BallBot will
come across (e.g. tennis balls). The value is equal to the voltage
produced across the reciever when an echo is recieved off that type of
surface at a distance of one metre.

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00000a90  20 6e 65 63 65 73 73 61  72 79 20 66 6f 72 20 74  | necessary for t|
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00000ad0  79 20 73 79 73 74 65 6d  73 20 6d 61 79 20 62 65  |y systems may be|
00000ae0  20 61 64 64 65 64 20 74  6f 20 64 65 74 65 63 74  | added to detect|
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00000b30  74 74 65 72 0d 0d 54 68  65 20 63 69 72 63 75 69  |tter..The circui|
00000b40  74 72 79 20 66 6f 72 20  74 68 69 73 20 73 6f 6e  |try for this son|
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00001950  74 20 61 70 70 65 61 72  73 20 74 68 61 74 20 76  |t appears that v|
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00001a70  73 20 70 72 6f 70 6f 72  74 69 6f 6e 61 6c 20 74  |s proportional t|
00001a80  6f 20 74 68 65 20 74 69  6d 65 20 74 61 6b 65 6e  |o the time taken|
00001a90  20 66 6f 72 20 74 68 65  20 65 63 68 6f 20 74 6f  | for the echo to|
00001aa0  20 62 65 20 72 65 63 69  65 76 65 64 2c 20 77 65  | be recieved, we|
00001ab0  0d 63 61 6e 20 63 6f 6e  76 65 72 74 20 74 68 69  |.can convert thi|
00001ac0  73 20 74 6f 20 73 61 79  69 6e 67 20 74 68 61 74  |s to saying that|
00001ad0  20 74 68 65 20 70 72 6f  64 75 63 74 20 6f 66 20  | the product of |
00001ae0  74 68 65 20 74 69 6d 65  20 65 6c 61 70 73 65 64  |the time elapsed|
00001af0  20 73 69 6e 63 65 20 74  68 65 0d 75 6c 74 72 61  | since the.ultra|
00001b00  73 6f 6e 69 63 20 62 6c  69 70 20 77 61 73 20 74  |sonic blip was t|
00001b10  72 61 6e 73 6d 69 74 74  65 64 20 61 6e 64 20 74  |ransmitted and t|
00001b20  68 65 20 69 6e 70 75 74  20 76 6f 6c 74 61 67 65  |he input voltage|
00001b30  20 69 73 20 61 20 63 6f  6e 73 74 61 6e 74 20 76  | is a constant v|
00001b40  61 6c 75 65 0d 66 6f 72  20 70 61 72 74 69 63 75  |alue.for particu|
00001b50  6c 61 72 20 73 75 72 66  61 63 65 73 2e 20 54 68  |lar surfaces. Th|
00001b60  69 73 20 69 73 20 6d 6f  72 65 20 75 73 65 66 75  |is is more usefu|
00001b70  6c 20 74 68 61 6e 20 64  69 73 74 61 6e 63 65 20  |l than distance |
00001b80  77 69 74 68 20 72 65 67  61 72 64 20 74 6f 0d 64  |with regard to.d|
00001b90  65 73 69 67 6e 69 6e 67  20 74 68 65 20 42 61 6c  |esigning the Bal|
00001ba0  6c 42 6f 74 20 68 61 72  64 77 61 72 65 2e 20 47  |lBot hardware. G|
00001bb0  72 61 70 68 73 20 66 6f  72 20 76 6f 6c 74 61 67  |raphs for voltag|
00001bc0  65 20 78 20 64 69 73 74  61 6e 63 65 20 66 6f 72  |e x distance for|
00001bd0  20 65 63 68 6f 0d 74 65  73 74 73 20 61 72 65 20  | echo.tests are |
00001be0  70 6c 6f 74 74 65 64 20  62 65 6c 6f 77 3a 0d 0d  |plotted below:..|
00001bf0  54 68 65 20 63 6f 6e 73  74 61 6e 74 20 76 61 6c  |The constant val|
00001c00  75 65 20 6f 66 20 74 68  65 20 70 72 6f 64 75 63  |ue of the produc|
00001c10  74 20 6f 66 20 76 6f 6c  74 61 67 65 20 61 6e 64  |t of voltage and|
00001c20  20 64 69 73 74 61 6e 63  65 20 63 61 6e 20 62 65  | distance can be|
00001c30  20 66 6f 75 6e 64 20 66  6f 72 0d 64 69 66 66 65  | found for.diffe|
00001c40  72 65 6e 74 20 73 75 72  66 61 63 65 73 20 66 6f  |rent surfaces fo|
00001c50  72 20 74 68 65 20 67 69  76 65 6e 20 73 70 65 61  |r the given spea|
00001c60  6b 65 72 73 20 61 6e 64  20 6f 75 74 70 75 74 20  |kers and output |
00001c70  61 6d 70 6c 69 74 75 64  65 2e 20 54 68 65 20 75  |amplitude. The u|
00001c80  6e 69 74 0d 6f 66 20 74  68 69 73 20 76 61 6c 75  |nit.of this valu|
00001c90  65 20 69 73 20 74 68 65  20 76 6f 6c 74 2d 6d 65  |e is the volt-me|
00001ca0  74 72 65 20 28 56 6d 29  2e 20 57 6f 72 6b 20 69  |tre (Vm). Work i|
00001cb0  73 20 63 75 72 72 65 6e  74 6c 79 20 69 6e 20 70  |s currently in p|
00001cc0  72 6f 67 72 65 73 73 20  74 6f 20 74 72 79 0d 74  |rogress to try.t|
00001cd0  6f 20 66 69 6e 64 20 61  63 74 75 61 6c 20 76 61  |o find actual va|
00001ce0  6c 75 65 73 20 6f 66 20  74 68 69 73 20 66 6f 72  |lues of this for|
00001cf0  20 74 68 65 20 6b 69 6e  64 20 6f 66 20 6f 62 6a  | the kind of obj|
00001d00  65 63 74 73 20 77 68 69  63 68 20 42 61 6c 6c 42  |ects which BallB|
00001d10  6f 74 20 77 69 6c 6c 0d  63 6f 6d 65 20 61 63 72  |ot will.come acr|
00001d20  6f 73 73 20 28 65 2e 67  2e 20 74 65 6e 6e 69 73  |oss (e.g. tennis|
00001d30  20 62 61 6c 6c 73 29 2e  20 54 68 65 20 76 61 6c  | balls). The val|
00001d40  75 65 20 69 73 20 65 71  75 61 6c 20 74 6f 20 74  |ue is equal to t|
00001d50  68 65 20 76 6f 6c 74 61  67 65 0d 70 72 6f 64 75  |he voltage.produ|
00001d60  63 65 64 20 61 63 72 6f  73 73 20 74 68 65 20 72  |ced across the r|
00001d70  65 63 69 65 76 65 72 20  77 68 65 6e 20 61 6e 20  |eciever when an |
00001d80  65 63 68 6f 20 69 73 20  72 65 63 69 65 76 65 64  |echo is recieved|
00001d90  20 6f 66 66 20 74 68 61  74 20 74 79 70 65 20 6f  | off that type o|
00001da0  66 0d 73 75 72 66 61 63  65 20 61 74 20 61 20 64  |f.surface at a d|
00001db0  69 73 74 61 6e 63 65 20  6f 66 20 6f 6e 65 20 6d  |istance of one m|
00001dc0  65 74 72 65 2e 0d                                 |etre..|
00001dc6
BallBot/Part3.m0
BallBot/Part3.m1
BallBot/Part3.m2
BallBot/Part3.m4
BallBot/Part3.m5

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