Ricochet Technologies
The Homing Disc
Table of Contents
Table of Contents
1
List of Tables
2
List of Figures
3
Abstract
4
1.
Introduction
5
2.
Background Information
6
3.
2.1 Small Size
6
2.2 Ruggedness
6
2.3 Economical
7
2.4 Power Efficient
7
Electrical & Mechanical Design
3.1
Transmitter and Receiver
8
3.2
Antennas
9
3.2.1
Transmitter Antenna
10
3.2.2
Receiver/ Handheld Antenna
12
3.3
4.
8
Data Processing
13
3.3.1 Microcontroller Options
14
3.3.2 The 16F876
15
3.3.3 PIC Programmer
16
3.3.4 The Code
17
3.4
Visual Output
19
3.5
Transmitter and Handheld Casings
20
Project Analysis
23
4.1
Power Analysis
23
4.2
Cost Analysis
24
4.3
Problems Encountered
25
5.
Conclusions
27
6.
Cited References
28
7.
References
29
Appendix A: PIC Code
Matthew Beau Nychka
31
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Niilo Van Steinburg
Ricochet Technologies
The Homing Disc
List of Tables
TABLE 1: MICROCONTROLLER COMPARISONS
14
TABLE 2 : 16F876 RELEVANT PINOUT DESCRIPTIONS
16
TABLE 3 : VOLTAGE RANGES FOR LEDS
19
TABLE 4: CURRENT DRAWS OF PRIMARY COMPONENTS WITHIN HOMING BEACON
23
TABLE 5: COSTS ($CAD) OF PRIMARY COMPONENTS WITHIN HOMING BEACON
24
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Ricochet Technologies
The Homing Disc
List of Figures
FIGURE 1 - VERTICAL DIPOLE AZIMUTH PATTERN
10
FIGURE 2 - TURNSTILE ANTENNA AZIMUTH PATTERN
11
FIGURE 3 : 16F876 PIN DIAGRAM
15
FIGURE 4 - PIC PROGRAMMER CIRCUIT DESIGN
16
FIGURE 5 - HANDHELD DATA FLOW DIAGRAM
17
FIGURE 6 - HAND HELD SIGNAL STRENGTH
19
FIGURE 7 - BASIC TRANSMITTER CIRCUIT DIAGRAM
21
FIGURE 8 - BASIC RECEIVER CIRCUIT DIAGRAM
22
Matthew Beau Nychka
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Niilo Van Steinburg
Ricochet Technologies
The Homing Disc
Abstract
This report details the design process followed in the creation of the Homing Disc, a
transmitter-receiver combination that will help a golfer find his missing disc.
The
transmitter is attached to an existing golf disc and is designed to meet the primary
specifications of being small, power efficient, and to withstand a variety of rugged
environments. The antenna used by the transmitter is a turnstile antenna with folded
dipoles to have an omnidirectional radiation pattern without a vertical dipole antenna.
The receiver is contained within a small hand-held device and measures the signal
surrounding it, displaying the varying power levels to the user in order to pinpoint the
disc's location. The antenna used by the receiver is a half-wave dipole antenna. It reads
the signal strength of the signal and transforms that into a usable analog voltage.
The receiver outputs a measure of the received signal strength and it is taken into the PIC
microcontroller, where it is analyzed. The PIC differentiates between the different signal
levels and outputs them using port B to six LEDs.
This report will provide the reader with information covering the choice in transmitters,
receivers, antennas, power sources, microcontrollers, and other components. It will also
detail the alternatives to these choices.
Finally an overview of the project and discussion regarding power and cost efficiency
will be presented, along with information on any problems encountered, and whether or
not this endeavor is marketable or not.
Matthew Beau Nychka
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Niilo Van Steinburg
Ricochet Technologies
The Homing Disc
1. Introduction
Ricochet Technologies is a university group consisting of Matthew Beau Nychka, an
electrical engineering undergraduate student, and Niilo Van Steinburg, a computer
engineering undergraduate student, supervised by Dr. Peter Dreissen. Our research focus
is in developing a miniature, power efficient homing beacon to be used on a Frisbee golf
disc. The time duration for this work is three months as per University of Victoria’s
ELEC/CENG 499A course guidelines.
Frisbee disc golf is a sport that has been rapidly growing since 1995. A player searching
for a lost disc through bushes on a course is an all too familiar sight. As most courses are
heavily treed and on rugged terrain, a disc that sails off course is often a disc lost.
Nighttime golfing adds its own obvious difficulties. A homing device designed to locate
discs hidden by brush or darkness can save both playing time and money.
Ricochet Technologies set out to solve this problem by designing a small, aerodynamic,
and lightweight transmitter that could be attached to the bottom of a Frisbee golf disc.
The purpose of this transmitter would be to radiate a high frequency radio (RF) signal
during a game so that a user would be able to track down a lost disc during a game. The
user would carry with him a pocket sized receiver that he could use to find his disc. The
receiver reads the signal strength and outputs it to a visual display to indicate to the user
whether or not he is pointing the receiver in the direction of the beacon.
With this in mind, please read on as we dive right into the details.
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Niilo Van Steinburg
Ricochet Technologies
The Homing Disc
2. Background Information
This portion of the report will focus on the goals of the project, both electrical and
mechanical, and will act as a constant base for the design and materials used to create the
homing beacon.
2.1 Small Size
In the sport of disc golf, a modified Frisbee disc is thrown towards a target. The sport is
usually played in a setting with a lot of brush and harsh terrain; consequently, the discs
are made to respond to the thrower very precisely. The typical Frisbee golf disc weighs
approximately 165 grams, is approximately 20cm in diameter, and has a height of 2cm.
Due to this small size and the aerodynamics of the disc, anything substantial added to the
body of the disc would result in an unfavorable performance. Therefore it was in our
user’s best interests that we create the device attached to the disc to be small enough to
have a negligible effect upon flight.
2.2 Ruggedness
The challenge and novelty of the sport are based upon the harsh nature of the courses.
The number of trees and rocks the disc contacts at high speed during one game are
countless. As well, cliffs and swamps are regular obstacles within a course.
Our designed casing reflects the need to have a transmitter contained within a water and
dust- proof casing for protection. The hand-held unit, though not subjected to the same
stresses as the disc unit, would also have to be made durable and as resistant to the
elements as possible.
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Ricochet Technologies
The Homing Disc
2.3 Economical
The average golf disc costs $15 CAD and has a lifetime of around 15 games. An avid
disc golfer will carry close to five discs with him during a game. This mirrors traditional
golf in that there are discs made for a variety of purposes: long-range, short-range, left
curve, S-curve, etc. When the costs of the discs themselves and their lifetimes are
factored in with the possibility of losing one to brush or darkness, the disc golfer’s costs
may increase drastically.
Our goal was to create a device that could be sold for close to $20, as suggested by polled
disc golfers. The device was designed to have a long lifetime, as well as an easily
replaceable and commercially sold battery.
2.4 Power Efficient
As a result of need to keep the device economical, we needed to address the requirements
of the transmitter. A long life, as well as the right power source meant that we addressed
all of our design with the concept of power efficiency in mind.
One of the smallest and most commercially available batteries to date is the coin cell
battery. Typically these run at a 3V supply and have a lifetime of between 190 and 320
mAh, depending on size of the coin cell itself. For an average game of 45 minutes over
the time of 15 games, a drain of 11.25mA, while activated, would be required for the
homing beacon to last as long as a disc before battery replacement.
An additional component necessary to the design of a power efficient device is the
addition of an LED to alert the user as to whether the device is on or off. This small extra
would potentially save the user the cost of dozens of batteries while draining only a
minute amount of current itself.
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Niilo Van Steinburg
Ricochet Technologies
The Homing Disc
3. Electrical & Mechanical Design
3.1
Transmitter and Receiver
To begin our research, we looked into a number of similar devices commercially
available today. Our research led through wildlife tracking units, avalanche beacons,
garage door openers, and remote key finders. Each product, while it taught us a great
deal about RF propagation, was perfect for its own application and impossible to use as a
template for our own.
Our goal in the use of the transmitter and receiver is to transmit a signal from disc to
hand-held receiver and to have that receiver measure the signal strength to notify the user
as to whether or not they were facing the right direction in search of his disc. The data
being sent across from transmitter to receiver is, in itself, unimportant. The significant
information is the Received Signal Strength Indication (RSSI). The receiver would need
to read the level of the signal and output it in a form that can easily be translated to a
visual display for the user.
The initial transmitter and receiver chosen were the surface mounted TXM/RXM-433LC-S [1], based solely on size and cost. After further research into antenna size and
specifications; however, we came to the conclusion that we needed to increase our
frequency to decrease the antenna size and make them more compatible with our goals.
Narrowing down our search parameters to receivers with an RSSI output at a 600MHz +
frequency offered any number of choices, but only a few reasonable ones. A number of
receiver/transmitter pairs, such as the Radiometrix RX2A-433-64 [2] were ideal for our
purposes but were too large for our compact design.
The final choice was the TDK5101 and TDA5201 [3], transmitter and receiver
respectively, by Infineon Technologies. Although they are one of the most versatile
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Ricochet Technologies
The Homing Disc
wireless communication sets on the market and coincidentally a very heavy-handed
solution to a simple problem, it was also one of the smallest and most economical
solutions.
The signal was sent from the TDK5101 ASK transmitter at 650MHz. Because the signal
itself, not the data, is the concern in this application we tie the data input high at powerup of the circuit. The transmitter is a very low cost and power efficient device as detailed
further in section 4.
The receiver TDA5201 is where the solution turns out to be overkill. The receiver
contains a low noise amplifier, a double balanced mixer, a fully integrated VCO, a PLL
synthesizer, a crystal oscillator, a limiter with RSSI generator, a data filter, a data
comparator, and a peak detector. While we only use the RSSI generator to out put an
analog 0.8 to 2.8 Volt signal, the chip incorporates most of these features into calculating
the best-filtered RSSI possible.
3.2
Antennas
The greatest difficulty in our design was the choice of antennas to be used with either the
transmitter or receiver. For each side of our transmission, we required very different
behaviors from our antennas.
Our choice in antennas is based upon five main
requirements [4]:

Gain/ Directivity

Pattern

Frequency

Polarization

Input Impedance
When looking over these criteria, we can choose our primary requirements to be pattern,
frequency, polarization, and input impedance. We will incorporate our gain requirements
into our need for specific radiation patterns. We choose not to concentrate on gain itself
specifically due to the short range this device will be used over.
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Niilo Van Steinburg
Ricochet Technologies
The Homing Disc
For our project, we look specifically at designing our antennas around a 630MHz signal,
chosen after much research into availability and cost of transmitters and receivers. This
information is discussed in more detail in section 3.1 above. The importance of this in
regards to antenna calculations is that we have an effective wavelength of λ = 46.15cm.
The input impedance, as per the transmitter and receivers chosen was to be 50 Ohms for
optimal performance.
3.2.1 Transmitter Antenna
The transmitter antenna had a number of requirements. Due to the need for size and the
design goal of making a transmitter that would be reusable from disc to disc, we needed
to fit the transmitter with a small antenna that would fit within the casing. Focusing on
the criteria we had to choose our antenna by we realize the ideal pattern would be that of
an omni-directional antenna. The disc would need to radiate a signal 360 degrees around
it while it lies flat on the ground. The ideal azimuth (horizontal plane) pattern is shown
below:
Figure 1 - Vertical Dipole Azimuth Pattern
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Niilo Van Steinburg
Ricochet Technologies
The Homing Disc
Due to the nature of the game it would be impossible to mount a vertical dipole, the
obvious choice for such a pattern, on the disc. We analyzed a number of alternatives in
our search for the right choice.
Below I will discuss two to the options and the
conclusions reached.
We began with looking at the full wave loop antenna due to its almost isotropic response
when lying flat on the ground. The effective nulls in the transmitted signal run parallel to
the ground and should not adversely affect the user. Due to its construction, the loop
antenna is very easy to match as well. The full wave loop antenna would have a diameter
of 0.147 m or 14.7 cm and an effective gain of approximately 3.14dB over isotropic
performance.
Finally we studied the turnstile antenna[5]. Essentially, the turnstile antenna consists of
two folded dipoles perpendicular to each other. One dipole is connected to the main feed
line, the 50-Ohm line from the transmitter. Between the feed point of the first and second
folded dipole, we run a 1/4 wavelength (11.5cm) section to effect the required 90-degree
phase shift between the two dipoles. It is this phase shift that gives the turnstile its nearly
omni-directional pattern. The resulting pattern is a blunted circle with only a 1-dB
decrease from maximum gain along two of the flattened edges. We see the radiation
pattern below:
Figure 2 - Turnstile Antenna Azimuth Pattern
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Ricochet Technologies
The Homing Disc
The chosen turnstile antenna radiates a near isotropic pattern and has an approximate gain
of 0.86dB less than isotropic performance. While we can note that the circular antenna
does have a better gain overall, our priority is to have a small antenna, and therefore a
small homing device.
We also note that the turnstile antenna has a horizontal polarization. Therefore, whatever
antenna is used for the receiver will need to be horizontally polarized as well.
3.2.2 Receiver/ Handheld Antenna
Our initial approach to designing the receiving antenna was to choose an antenna with a
narrow beam width in order to isolate the direction of the transmitted signal. Following
this rationale we invested a great deal of time into researching yagi, helical, parabolic,
horn, and microstrip antennas. However, due to either size or orientation within the
handheld device, each was rejected.
Yagis, parabolic, helical, and horn antennas, while they have a preferred pattern and
directivity, are far too large for our designed product. The microstrip antennas have two
unfortunate problems. They are most suitable when the maximum dimension of the
antenna is a quarter or half wavelength. With that in mind, using either patch antennas or
waveguides will lead to a bulky hand held device due to antenna orientation. As well,
due to dielectric loading, the operating frequencies of small transmitter/receiver systems
are typically restricted to bands above 800MHz, which would not work well with our
system. [6]
We investigated antennas used in other applications.
The coast guard uses a dual
perpendicular full wave loop antenna to calculate exact directions of received signals.
However, while we could calculate exact direction by signal phase/comparison analysis
without moving the hand-held unit; the antenna, itself, would be far too large to
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Ricochet Technologies
The Homing Disc
incorporate into a compact design and too expensive, as well as being out of the scope of
our project.
Noting that directionality in an antenna pattern was not going to work due to various
reasons we looked into the idea of using the nulls and reversing our calculations, which
brought us to our ideal solution. Using a half-wave dipole antenna, we could make a thin,
compact hand-held unit that would show a null when pointed directly at the receiver and
would output a high RSSI analog voltage when pointed any other direction. The only
hurdle from that point was to test the received signals and null-width to correctly output
the 0.8-2.8V RSSI to the visual display for the user. This is covered in more detail in
sections 3.3 and 3.4.
The one problem encountered with this approach is that if the user is standing no-where
near the transmitter, or facing directly away from it. The hand held display will show
display indicating that the user is pointing in the right direction. While this is a large
potential problem we must remember that the user will have a general idea of where the
disc landed and should not end up facing this predicament in any case.
3.3
Data Processing
The hand-held unit basically houses the brains of this homing system.
The signal
strength is captured by the receiver, which then feeds it to a microcontroller. This
microcontroller is required to process the signal data and present it to the user in a useful
form.
We went through several stages in determining what sort of microcontroller to use in the
hand-held unit. As neither of us was familiar with microcontrollers other than the
Motorola 68HC11, we first started to conduct research on what our options were. From
the beginning we knew that we only needed something simple: we wouldn't need much
space for code, we would only need a few input/output pins, and there wasn't much in the
way of size constraints (most chips are much smaller than a 9V battery). The main
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Ricochet Technologies
The Homing Disc
requirement that we kept an eye out for was A/D conversion capability, as we would
likely need that for analysis of the information gained from the receiver. Also, we
wanted to select a chip that we could easily acquire the necessary peripherals for (to
program it). Of course, price was a factor as well, as we desired to keep the components
as cheap as possible.
3.3.1 Microcontroller Options
After a great deal of online research and meetings with microcontroller experts, we
narrowed it down to three options. Internet research first led us to the PIC 12F675. This
microcontroller is quite cheap yet has A/D capabilities.
One microcontroller type that was recommended to us was the Atmel brand. The main
reason for this was that they were familiar with it and all software and equipment needed
for programming these chips was already in the Engineering Lab Wing. After some
research on these chips, it seemed that the AT90LS4433 was suitable for our needs at a
modest price.
A friend, a hobbyist in PIC programming, strongly recommended the PIC 16F876
microcontroller. He felt that it was our best option, as it is durable, small in size, and has
a small, easy-to-learn instruction set. As well, he would be able to help us set up our own
programmer for the PIC.
The following is a table that compares some of the more pertinent aspects of these chips:
Chip
Package
I/O
Code
A/D
Cost ($US)
PIC 12F675
dip 8
6
1k
4 Ch. 10 Bit
3.05
AT90LS4433
dip 28
20
4k
6 Ch. 10 Bit
8.44
PIC 16F876
dip 28
22
8k
5 Ch. 10-Bit
11.81
Table 1: Microcontroller Comparisons
Matthew Beau Nychka
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Niilo Van Steinburg
Ricochet Technologies
The Homing Disc
We first decided that the 12F675 was probably not a good choice, since it only had 6 I/O
pins. As we had not yet decided what sort of visual display we'd implement, this number
of pins could easily turn out to be inadequate. In the end, we decided to go for the PIC
16F876. Even though it was more expensive than the Atmel chip, we felt that having the
knowledge of a friend at our disposal would be a great boon. Due to its popularity, there
are a lot of sample programs available on the internet to speed up the learning process.
As well, should we decide to expand upon the capabilities of the Homing Disc's
capabilities, the 16F876 would be able to accommodate us further.
3.3.2 The 16F876
PIC microcontrollers are a popular family of microcontrollers developed by Microchip
Technology. As mentioned already, the 16F876 is a fairly versatile chip and will be more
than adequate for our needs. It has a wide operating range, from 2.0 V to 5.5 V, which
will facilitate its coupling with the receiver.
Figure 3 : 16F876 Pin Diagram
Pin Name
Pin#
Description
MCLR'/VPP
1
Master Clear (Reset) input or programming voltage input. This
pin is an active low RESET to the device.
AN0
2
Pin 0 of Port A. This pin will be initialized as the analog input for
our signal strength.
VSS
8, 19
Ground reference for logic and I/O pins.
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The Homing Disc
OSC1/CLKIN
9
Oscillator crystal input/external clock source input.
OSC2/CLKOUT
10
Oscillator crystal output. Connects to crystal or resonator in
crystal oscillator mode.
VDD
20
Positive supply for logic and I/O pins.
RB0 - RB5
21-26
Port B is a bi-directional I/O port. These 6 pins will be designated as
output pins to control the LED display.
Table 2 : 16F876 Relevent Pinout Descriptions
3.3.3 PIC Programmer
Microcontrollers need to be programmed, so programmers must be purchased or built in
order to do this. After looking into our options, we decided it would be much cheaper to
build our own programmer.
We were designed a schematic (Figure 4) to build a
controller for our PIC and purchased the necessary parts for it. Programming the PIC
involved connecting the serial connection to a Com port on the back of the computer.
Then MP Lab IDE, a software program intended for programming PICs, is used to
download code onto the microcontroller.
Voltage
Regulator
16F876
Max 232
Figure 4 : PIC Programmer Circuit Design
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Ricochet Technologies
The Homing Disc
The extra microchip used in this programmer set-up is a Max 232. It is a driver/receiver
and acts as an interface between the PIC and the computer during programming.
3.3.4 The Code
The code that we needed to operate the hand-held was kept very simple. Once we
determined the exact nature of the input from the receiver, we knew we only needed to
read the data, process it, and output the result to our visual display (6 LEDs). All data
flow was in a single direction as indicated by figure 5.
Receiver
Send signal
Strength
Process
Signal
Activate
LEDs
Display
Figure 5 : Handheld Data Flow Diagram
The code follows a very simple process of reading the signal strength and comparing the
digital representation of it to several pre-defined values. The microcontroller stays in a
continuous loop doing this. Since the signal strength is lowest when the hand-held is
pointing directly at the disc, this must correspond with all 6 LEDs being turned on.
Therefor, the code will turn on the LEDs as the signal strength decreases and shut them
off again as the signal gains strength. Note that the base LED will always be turned on
when the hand-held is operating. The entire algorithm is summarized in the following
pseudo-code:
; define parameters
LEVEL0 equals 2.5 Volts
LEVEL1 equals 2.35 V
LEVEL2 equals 2.2 V
LEVEL3 equals 2.1 V
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The Homing Disc
LEVEL4 equals 2.0 V
LOOP1
Turn off the 2nd LED
LOOP2
Turn off the 3rd LED
LOOP3
Turn off the 4th LED
LOOP4
Turn off the 5th LED
LOOP5
Turn off the 6th LED
LOOP6
STRENGTH = signal strength from receiver
if (STRENGTH < LEVEL0)
Turn on LED #2
else
GOTO LOOP1
if (STRENGTH > LEVEL3)
Turn on LED #3
else
GOTO LOOP2
if (STRENGTH > LEVEL2)
Turn on LED #4
else
GOTO LOOP3
if (STRENGTH > LEVEL1)
Turn on LED #5
else
GOTO LOOP4
if (STRENGTH > LEVEL0)
Turn on LED #6
else
GOTO LOOP5
GOTO LOOP6
Originally, our PIC was programmed to read the signal strength and turn on LEDs as the
signal showed itself to be strong. However, due to RF reflection and scattering in the
signal over such a short-range [7], we typically received a stronger signal than we should
have. Because of this, we decided upon a new antenna set-up, as described in section
3.2.2. We then re-programmed the microcontroller to reflect the change. See Appendix
A for final source code.
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Ricochet Technologies
The Homing Disc
The A/D converter changes the analog input to a value relative to VDD. With the receiver
sending a voltage from 0.8V to 2.8V to the microcontroller, we had to designate which
values would correspond to which LEDs. Once the divisions were made, the binary
values for these voltages had to be calculated for use in code. We did this by first
dividing the boundary voltages by the reference voltage (5V). We then multiplied these
results by 255 (the maximum value for 8 bits). The results, once rounded and converted
to binary, became our binary boundary values. Note that the A/D converter is 10 bits; it
was easiest in terms of programming to simply drop the lowest two bits and work with an
8-bit number. The error resulting from this is insignificant (the maximum error would be
for our lowest signal value - 0.8V - and this gives approximately a 0.39% error).
Voltage Range
# LEDs On
Boundary Voltage
Boundary Voltage /
Ratio times 255 then
Reference Voltage (5V)
converted to binary
2.5 - 2.8 V
1
n/a
n/a
n/a
2.35 - 2.5 V
2
2.5
0.5
1010110
2.2 - 2.35 V
3
2.35
0.47
01111000
2.1 - 2.2 V
4
2.2
0.44
01110000
2.0 - 2.1 V
5
2.1
0.42
01101011
0.0 - 2.0 V
6
2.0
0.4
01100110
Table 3 : Voltage Ranges for LEDs
3.4
Visual Output
The results from the microcontroller needed to be displayed to the user in some form. In
the beginning, we contemplated using an analog display, an LCD, or simple LEDs. Due
to time and budgetary constraints, we felt that it would be best to start off with the
simplest display. Six LEDs were then incorporated into our hand-held design (please
refer to Figure 6 below).
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Ricochet Technologies
The Homing Disc
Figure 6 - Hand Held Signal Strength Indicator
These LEDs will be turned on or off according to the signal strength picked up by the
receiver. Refer to section 3.3.4 (Table 3 above) to see what values were designated for
each LED.
3.5
Transmitter and Handheld Casings
The majority of the constraints involved in this project are applicable more to the
transmitting side of this pair of devices. The four main goals regarding the casings were
to make them:

water and dust-proof,

easily accessible to change batteries,

shock resistant,

aerodynamic, and

easy to move from one disc to another
In order to keep the beacon water and dust resistant, it is sealed completely. The on/off
switch is a reed switch, turned on by a small magnet that is attached to the base of the
hand-held unit. The only opening on either device will be for the batteries. The 3 volt
battery in the beacon is accessable by using a coin or other similar object to open or close
the compartment where the coin is stored. This will be sealed with a simple O-ring. The
beacon is shock resistant due to the extremely tight specifications in the plastic moulding
around the components, allowing no movement, banging, or bumping.
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Ricochet Technologies
The Homing Disc
By making the beacon as small as possible, the size and weight are kept down, and
therefore, the aerodynamics of the original product are unaffected by the beacon. The
schematic of the transmitter is shown in Figure 7 below:
Figure 7 - Basic Transmitter Circuit Diagram
We can note that this figure is not at all to scale and quite a bit larger than the device
would be. The largest dimension in the design is the antenna itself, measuring 11.5 cm
across at its largest. The largest component is the battery, which is as large as the rest of
it put together.
The beacons are interchangable due to the construction of the plastic moulding. The
combination of the sticky substance on the flat of the beacon and the tiny metal barbs will
allow the user to attach it to any disc.
As mentioned above, the hand-held unit does not need to stand up to the rigors that the
beacon will need to endure, but it is important that it can tolerate some abuse as it’s not at
all strange to see a disc golfer climbing a cliff mid-game. A disc golfer traversing rugged
courses also does not want a bulky contraption to carry around.
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Ricochet Technologies
The Homing Disc
To solve these concerns, first, the hand-held unit is sealed except for in two spots. The
end of the unit (sketched in Figure 6 above) is accessable for replacement of the 9 volt
battery and there will be a small on/off switch on the side of the device.
Secondly, our design for the hand-held kept the need for a small size in mind, leaving the
golfer with nothing to carry but a device the size of an average candy bar. As with the
transmitter, the largest dimension of the hand-held receiver is the 23cm dipole antenna, as
shown in the figure 6 above.
Figure 8 - Basic Receiver Circuit Diagram
The hand-held unit also had to be small. A disc golfer traversing rugged courses would
not want a bulky contraption to carry around. Our design for the hand-held kept this
important constraint in mind, leaving the golfer with nothing to carry but a device the size
of an average candy bar. As with the transmitter, the largest dimension of the hand-held
receiver is the 23cm dipole antenna, as shown in the figure 8 above.
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The Homing Disc
4. Project Analysis
4.1
Power Analysis
As analyzed above, in section 2.4, we would like our homing beacon to run at
approximately 11.25mA on average in order to have it outlive the average golf disc.
Looking at the breakdown in current draws from the parts used in the existing circuit, we
see the following:
Component
Power On
Power off
D-Type Flip Flop
11 μA
11 μA
TDA5101 Transmitter
7 mA
0.3 nA
Dual NAND Gate Debouncer
1.1 μA
1.1 μA
Total
≈7.012mA
≈12.1μA
Table 4: Current Draws of Primary Components Within Homing Beacon
We see that the current draws from the added components, running at 3V, add up to near
7.012 mA when the device is turned on. This will allow the user to have at most 27.1
hours of continuous use. If the disc remains off, the battery will last 15702 hours or 654
days in a powered down state.
We see that this is a very reasonable expectation of the product and can conclude that
from a power efficiency standpoint, it has superior performance.
The hand-held device is much easier to deal with. As its requirements are not nearly as
stringent in terms of size or power efficiency, we have a number of options to provide it
with an acceptable power source. The two major components in the hand-held receiver
are the PIC microcontroller and the receiver, each requiring 3 and 5V respectively. The
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best solution for this is to use a simple, commercially available 9-volt battery. These
have a long life and are very easy to replace.
4.2
Cost Analysis
A major consideration as to whether or not this is a marketable product is the cost
analysis. As mentioned above, a reasonable price for the product is approximately $20
CAD. We can view our major component costs as the primary expenses due to the fact
that small components such as resistors, capacitors, inductors and production costs can be
done for pennies once start-up costs have been taken care of. We see the breakdown of
primary component costs below.
Component
Cost ($CAD)
Cost ($CAD)
Single
Bulk
PIC 16F876 Micro-controller
10.73
6.85
TDA5101 Transmitter
3.43
2.80
TDA5201 Receiver
5.98
4.88
Reed Switch
1.19
0.44
Single D-type Flip Flop
0.63
0.23
3V Coin Cell Battery
0.66
0.32
Ceramic IF Filter
2.01
0.85
10MHz Crystal Oscillator
1.38
0.54
9.8438MHz Crystal Oscillator
2.86
1.72
3.58 MHz Ceramic Resonator
0.79
0.37
9V Battery
3.10
1.19
Total parts cost:
20.19
Table 5: Costs ($CAD) of Primary Components Within Homing Beacon
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The Homing Disc
We see that our costs are over our target costs by a fair amount and can conclude that
while the product is power efficient, without some significant changes to our design and
components used, the product is not marketable.
4.3
Problems Encountered
While it was a major aspect of our project to build the smallest, least obtrusive, solution
to our problem, it was also our downfall. With the equipment available to us in the UVic
labs, we were not able to complete the prototype on a printed circuit board (PCB). This
in itself is not a problem, but due to the methods used to prepare a working prototype on a
breadboard, we faced one very large obstacle. Using the breadboards, necessary wiring,
and soldering lead wires into the vias in the adapter PCBs increased the impedances
within the circuit and led to unfavorable reactions from the receiver and transmitter.
Such problems would be avoided moving the prototype from a breadboard setting to a
properly laid out PCB.
Another problem we faced, however within our control it was, was the side effects that
came from using a high frequency signal. Using a radio frequency (RF) as large as
650MHz we were able to make our antennas smaller, but had to sacrifice directivity of
our signal. As we see in the following equation from [8], the directivity is directly related
inversely to frequency squared
D
= 2ka + (ka)^2
= 4πa/λ + (2πa/λ)^2
α 1/ f^2
where a is the radius of the antenna.
On the transmitter side, this is not a bad thing as it helps us achieve a more isotropic RF
pattern. However, on the receiver side we would like to have a clear distinction between
the areas where the signal is strong and where the loss is complete. With this lack of
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The Homing Disc
directivity due to high frequency and small antenna size it complicates our signal strength
processing as was described in more detail within section 3.3.
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Ricochet Technologies
The Homing Disc
5. Conclusions
After coming to several dead-ends during our research, design, and implementation of
this project, we feel that we have developed a fairly good product. In the end, we chose
to go with a receiver and transmitter operating at 650 MHz to drop the antenna size. After
a great deal of research, we decided to use a turnstile antenna with folded dipoles for the
transmitter due to its resulting omnidirectional radiation pattern. We chose a dipole
antenna for the receiver, because of its omnidirectional coverage, but counted on reading
for the transmitter by lack of signal, using the nulls in the received signal. The
microcontroller we used is the PIC 16F876 which more than adequately met our
processing needs in the hand-held device.
Our final design is quite power efficient, small, aerodynamic, and strong meeting most of
our objectives.
Unfortunately, the cost of the components altogether would be
prohibitive to trying to market the Homing Disc as a product. Continue our work from
here, we will next look at ways to reduce the cost, the first act being to replace the
microcontroller with one that is cheaper. Perhaps we could replace other parts with
cheaper alternatives if given the time.
Overall this project has been a great learning experience for the two of us. Not only have
we learned and applied specific technical knowledge that we weren't previously familiar
with, but we have learned a great deal what is involved in project management.
Matthew Beau Nychka
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The Homing Disc
6. Cited References
[1]
Lynx Technologies, “LC Series Receiver Modules”, 2003, Available HTTP:
http://www.linxtechnologies.com/ldocs/pdfs/lcsreceivdg.pdf
[2]
Radiometrix, “UHF FM Receiver Module with RSSI”, July 2003, Available
HTTP: http://www.radiometrix.co.uk/products/rx2a.htm
[3]
Infineon Technologies, “Infineon Technologies Wireless Controls”, July 2003,
Available HTTP: http://www.infineon.com/cgi/ecrm.dll/ecrm/scripts/prod_cat.jsp?oid=9470
[4]
R. Karumudi, private communication, 2003.
[5]
L.B. Cebik, W4RNL, “The Turnstile Antenna on 10”, December 2001, Available
HTTP: http://www.cebik.com/a10/ant34.html
[6]
K.
Siwiak,
“Radiowave
Propagation
and
Antennas
for
Personal
Communications”, Norwood, MA, pp. 237: Artech House, 1995.
[7]
D. Djonin, private communication, 2003.
[8]
University of St. Andrews, “Directionality and Gain”, 2003, Available HTTP:
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part6/page2.html.
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The Homing Disc
7. References
Analytical Graphics, Inc., “Antenna Beam Types and Antenna Polarization”, May 1996,
Available HTTP: http://www.stk.com/resources/help/help/stk43/comm/CommRadar0302.htm#AntPolType
C. Balanis, Antenna Theory: Analysis and Design, New York: chapter 4, Wiley 1982.
Colorado Geographical Survey, ‘Summary of the Avalanche Beacon Test”, December
1998, Available HTTP:
http://geosurvey.state.co.us/avalanche/transceivers/LVS98/LVS98_summary.html
Digikey.com, Product Information and private communication, 2003, Available HTTP:
http://dkc1.digikey.com/ca/digihome.html
Infineon Technologies, “Infineon Technologies Wireless Controls”, July 2003, Available
HTTP: http://www.infineon.com/cgi/ecrm.dll/ecrm/scripts/prod_cat.jsp?oid=-9470D.
Jefferies, University of Surrey, “Antennas”, 2003, Available HTTP:
http://www.ee.surrey.ac.uk/Personal/D.Jefferies/antennas.html
R. Johnson, “Antenna Engineering Handbook”, 3rd ed., New York: McGraw-Hill, 1993.
Laboratory Manual for Elec 404: Microwave and Fiber Optics, UVic, Feb. 2002.
Lynx Technologies, “Antennas: Design, Application, Performance Notes”, July 1998,
Available HTTP: http://www.linxtechnologies.com/ldocs/zips/APNOTPDF.ZIP
MG Chemicals, “Positive Photo-fabrication Process Instructions”, 2003, Available
HTTP: http://www.mgchemicals.com/techsupport/photo_inst.html
Maxim/ Dallas Semiconductor, “Designing Remote Keyless Entry (RKE) Systems”,
2003, Available HTTP:
http://www.maxim-ic.com/appnotes.cfm/appnote_number/1773/ln/en
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The Homing Disc
The Millennium Education Group, “Antenna Systems”, 1998, Available HTTP:
http://www.tmeg.com/tutorials/antennas/antennas.htm
Dr. N. K. Nikolova, McMaster University, “Modern Antennas in Wireless Applications”,
Jan. 2002, Apr. 2003, Available HTTP:
http://www.ece.mcmaster.ca/faculty/georgieva/antenna_dload/
Omega Research Ltd., “Prototyping Surface Mount (SMD) adapters”, 2003, Available
HTTP: http://www.omega-research.co.uk/
D. M. Pozar, “A Review of Aperture Coupled Microstrip Antennas: History, Operation,
Development and Applications”, May 1996, Available HTTP:
http://www.ecs.umass.edu/ece/pozar/aperture.pdf
D. M. Pozar, Microwave Engineering, 2nd ed., Crawfordsville: John Wiley & Sons, Inc.,
1998
Radiometrix, “UHF FM Receiver Module with RSSI”, July 2003, Available HTTP:
http://www.radiometrix.co.uk/products/rx2a.htm
T.S. Rappaport, Wireless Communications, Principles and Practice, 2nd ed., Upper
Saddle River: Prentice Hall PTR, 2002
Reed Switch Developments Corp., “Bare Reeds and Magnets”, 2003, Available HTTP:
http://www.reedswitchdevelopments.com/
K. Siwiak, Radiowave Propagation and Antennas for Personal Communications,
Norwood, MA: Artech House, 1995.
University of St. Andrews, “Directionality and Gain”, 2003, Available HTTP:
http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part6/page2.html
Wireless World, Aerocomm Inc., “Antenna Tutorial”, 2000, Available HTTP:
http://www.awirelessworld.ch/appnotes/aerocomm/ant-tut.pdf
L.B. Cebik, W4RNL, “The Turnstile Antenna on 10”, December 2001, Available HTTP:
http://www.cebik.com/a10/ant34.html
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Appendix A: PIC Code
;--------------------------------------------------------------------;
; SHOWSIGNAL.ASM
Reads an analogue signal and displays its
;
;
strength on LEDs
;
;
(some of this code grabbed from ftp.microchip.com)
;
;--------------------------------------------------------------------;
list
p=16f876
; list directive to define processor
#include <p16f876.inc>
; processor specific variable definitions
ERRORLEVEL -224
; suppress annoying message because of tris
__CONFIG _CP_OFF & _WDT_ON & _BODEN_ON & _PWRTE_ON & _RC_OSC &
_WRT_ENABLE_ON & _LVP_ON & _CPD_OFF
;--------------------------------------------------------------------;
;
Define the values that measure the different levels of
;
;
signal strength.
;
;--------------------------------------------------------------------;
LEVEL0
LEVEL1
LEVEL2
LEVEL3
LEVEL4
EQU
EQU
EQU
EQU
EQU
ORG
0
10101101b
01111000b
01110000b
01101011b
01100110b
;
;
;
;
;
1
2
3
4
5
LED, 2.5V
LEDs, 2.35V
LEDs, 2.2V
LEDs, 2.1V
LEDs, 2.0V
; start at program memory location zero
;--------------------------------------------------------------------;
;
Set up 6 pins of PORT B to act as output (to the LEDs)
;
;
and turn all of them initially on.
;
;--------------------------------------------------------------------;
movlw
B'11000000'
tris
PORTB
; Set 6 lower bits of PORT B as outputs
movlw
B'00111111'
movwf
PORTB
; Turn on all 6 LEDs (start-up flash)
;--------------------------------------------------------------------;
;
Initialize the A/D converter
;
;--------------------------------------------------------------------;
clrf
ADCON1
; clear ADCON1 (AN0-4 set to analogue input
; Vref+ is Vdd and Vref- is Vss)
;--------------------------------------------------------------------;
;
Turn off any LEDs that should not be on
;
;--------------------------------------------------------------------;
Begin1
bcf
PORTB, 1
; Clear the 2nd LED
bcf
PORTB, 2
; Clear the 3rd LED
bcf
PORTB, 3
; Clear the 4th LED
Begin2
Begin3
Begin4
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bcf
PORTB, 4
; Clear the 5th LED
bcf
PORTB, 5
; Clear the 6th LED
Begin5
Begin6
;--------------------------------------------------------------------;
;
Begin A/D conversion
;
;--------------------------------------------------------------------;
bsf
ADCON0,GO
btfsc
goto
ADCON0,GO
Wait
; Start A/D conversion
Wait
; Wait for the conversion to complete
;--------------------------------------------------------------------;
;
Compare the measured signal strength to predetermined values ;
;
to determine how many LEDs to light up.
;
;--------------------------------------------------------------------;
movf
sublw
btfss
ADRESH, W
LEVEL0
STATUS, C
goto
bsf
Begin1
PORTB, 1
movf
sublw
btfss
ADRESH, W
LEVEL1
STATUS, C
goto
bsf
Begin2
PORTB, 2
movf
sublw
btfss
ADRESH, W
LEVEL2
STATUS, C
goto
bsf
Begin3
PORTB, 3
movf
sublw
btfss
ADRESH, W
LEVEL3
STATUS, C
goto
bsf
Begin4
PORTB, 4
movf
sublw
btfss
ADRESH, W
LEVEL4
STATUS, C
goto
bsf
Begin5
PORTB, 5
goto
Begin6
end
Matthew Beau Nychka
; Put signal strength into working register
; If carry bit in status register is 1,
; then the signal strength < LEVEL0
; Light up the second LED
; Put signal strength into working register
; If carry bit in status register is 0,
; then the signal strength < LEVEL1
; Light up the third LED
; Put signal strength into working register
; If carry bit in status register is 0,
; then the signal strength < LEVEL2
; Light up the fourth LED
; Put signal strength into working register
; If carry bit in status register is 0,
; then the signal strength < LEVEL3
; Light up the fifth LED
; Put signal strength into working register
; If carry bit in status register is 0,
; then the signal strength < LEVEL4
; Light up the sixth LED
; end of program
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The Homing Disc
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