Final Report
Free Space Optical Communications System
Team Blazers
Daniel Stromberg
Nathanael Weidler
Sean Palmer
December 07, 2010
1
Table of Contents
Executive Summary ................................................................................... Page 3
Block Diagram ............................................................................................ Page 4
Digital Signal Characterization ................................................................... Page 5
Laser and Photodiode Characterization...................................................... Page 6
Transmitter ................................................................................................ Page 8
Receiver ................................................................................................... Page 11
System-Level Functionality ...................................................................... Page 13
Charging Circuit and LED Indicator ........................................................... Page 14
Packaging................................................................................................. Page 15
Lessons Learned ....................................................................................... Page 16
Conclusion ............................................................................................... Page 16
Appendices
A-Concept Selection and Generation .............................................. Page 18
B-Functional Specification Document ............................................. Page 22
C-Project Schedule ......................................................................... Page 26
D-Operations Manual ..................................................................... Page 27
2
Executive Summary
The purpose of this product is to transmit digital music using a laser. It is meant for any
application where wired or wireless technology is less desirable. Our free-space optical system
is designed to transmit and receive a digital audio signal from a DVD player to a Stereo amplifier
across the room using inexpensive lasers in a line-of-sight configuration. The product consists of
a transmitter and a receiver. This semester’s variation on the design is to make the system able
to run off of a 9V NiCad rechargeable battery. Because of this restriction, our focus has been on
making a design with as low power consumption as is possible to maximize battery life and, as a
result, operation time. The battery is integrated into the system such that it can be plugged into
the wall to charge. Our project works at a variety of distances. It is rated for operation between
5 and 20 feet.
3
4
Digital Signal Characterization
In order to successfully process the digital audio signal, we first needed to know some of the
signal’s characteristics. Below are various measurements taken to familiarize ourselves with
the signal.
For our first test, we connected the DVD output directly into an oscilloscope. By viewing the
signal, we measured a peak to peak voltage level of 608 mV. By observing the digital
waveforms, we were also able to see that the data was being transmitted at a maximum rate of
5 MHz.
DVD Output (Voltage Level)
As can be seen in the above picture, the peak voltage for the DVD out was about 608 mV. The
lowest frequency that we found was about 4Mhz, making the bit rate about 4 million bits per
second. The rise and fall times of the audio signal were also quantified and can be seen in the
diagrams below. The rise time varied from about 56-72ns but tended to be around 67ns. The
fall time was much more consistent. Ranging from 46ns to 52ns it was measured to be around
48ns.
5
Fall Time Measurement
Rise Time Measurement
Laser and Photodiode Characterization
For testing the lasers we have used, we wanted to first identify the threshold level of each
laser. This is the current level at which the laser’s efficiency begins to increase rapidly. We also
wanted to get an idea of how much power the laser was transmitting. For testing these
6
attributes, we connected the laser to a current source and shined it on the optical power
detector using an optical attenuator which brought the measured power down by a factor of
1000. The measured data of this experiment is as follows:
Laser Power and Photodiode Characterization
Laser
Current (mA)
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
Laser 1
Output (nW)
5.5
5.9
6.5
7.6
9.25
11.2
14.4
19
29
260
950
1600
2100
2430
2650
2800
Laser 2
Output (nW)
6.3
7.2
8.9
10.9
13.6
17.1
22.6
31.7
105
1000
1900
2800
3500
3700
4600
6000
Photodiode Induced Photodiode
Current (µA)
Responsivity (A/W)
.04
6.349206
.1
13.88889
.18
20.22472
.3
27.52294
.44
32.35294
.91
53.21637
1.37
60.61947
2.28
71.92429
16.6
158.0952
107.9
107.9
193
101.5789
270
96.42857
330
94.28571
347
93.78378
372
80.86957
424
70.66667
From this experiment we are able to observe the threshold level of laser 1 to be around 18 mA
and the threshold of laser 2 to be around 15 mA. At these values, the output power begins to
display a rapid increase.
Also included in the above table are our measurements taken in the characterization of the
photodiode we have used for the final product. The measurements were taken using laser 2 as
the laser source at a distance of 6 in. to assure maximum power received at the diode. We put
an ammeter and the photodiode in series with a power supply set to deliver a reverse bias
voltage of 8V. As can be seen by the table, the Responsivity fluctuates. This is likely due to not
getting the laser focused such that all the optical power hits the detector.
7
Minimum Spot Size vs. Distance
The spot size on our laser was very close to a circle so we have defined spot size as the
diameter of the circle. The spot size at 20 feet was about 2.5cm and the spot size at 5 feet was
about 3mm. We calculated the beam divergence of the laser at 20 feet. We used the formula
arctan(r/L) = divergence. When r = 1.75cm L = 20 feet (609.6 cm) then arctan(1.75/609.6) =
0.00287 Rad.
Transmitter
8
The transmitter design consists of a single BJT with a resistor network to bias it on. We
feel that this is the most power efficient and feasible design. We don’t want to lose a lot of
current to ground through the resistor bias, so we are using an R1 resistor of 10K ohms and an
R2 resistor of 1k ohms. This biases the base at about 8V when the battery is at 9V and we lose
about 800uA through R2 to ground. It is designed to have a digital input signal of
approximately 1VPP at the base and it outputs a current through the laser ranging from 13 to
23 mA.
We have found that an emitter resistor of 330 ohms gives us an ideal current gain. We
have also found that moving the laser diode to the emitter from our initial design when it was
on the collector of the BJT gives us a more stable output with less current swing. This is
important to have less current swing because we want to keep the maximum current as low as
possible. We found that we were burning out lasers with the old design because the current
swing was too high. A simulated AC analysis can be seen below.
AC Analysis of current through the laser diode at 9V
9
The following DC analysis expresses the average current of the transmitter as the DC supply
loses power.
Battery voltage and Transmitter current
input
voltage
7.5
8
8.5
9
9.5
Transmitter
Current mA
15.9
17.1
18.5
19.8
20.9
Simulated DC Analysis of Current vs. Voltage
. Below are two graphs and a table. The table shows how current at the laser diode on the
transmitter decreased with time as the battery’s voltage decreased. The first chart is a typical
battery discharge at 24 mA. The second is the discharge curve of the battery connected to the
transmitter. For most of the test we were drawing less than 20 mA from the battery so it’s not
surprising we lasted more than the 5 hours on the typical discharge graph. In the end the
battery could give no more power after running the transmitter for 10 hours. We were very
pleased with this result as it is twice as long as the original specification.
10
Typical Battery Discharge (24 mA)
Tested Battery Discharge
10.5
10
9.5
9
8.5
8
7.5
7
6.5
6
0
1
2
3
4
5
6
7
8
9 10
Receiver
The design of our receiver was fairly simple. There were 2 stages of amplification. The first was
passive using a single resistor. The second was a low-power op-amp. We did a fair amount of
searching and found an appropriate amp. We ended up choosing the AD8011. It was designed
for use with optoelectronics. It has a very low quiescent power consumption, and has a GBW of
300MHz. Our first functioning design used a gain of 100 bringing the bandwidth down to 3MHz.
It did function without any audibly-discernable loss in quality, but in the end we changed it so
we would have better bandwidth.
Our final design had the photodiode revered biased and pulling current through a resistor
11
which was connected to the op-amp in a noninverting configuration. This gave us a total gain of
36700V/A. So when the laser is properly aimed at the detector, the signal output level was
around .8Vpp. We relied on the fact that it is a digital system. We didn’t drive the output all the
way up to the target 1Vpp since driving it would consume more current. One phenomenon that
we weren’t able to explain but seemed to work to our advantage was the fact that the signal
output reached its peak around 7V of input power. So as the receiver’s battery voltage slips, the
signal’s Vpp went up about 15% compared to 9V. So as less optical power was reaching the
photodiode due to the transmitter’s battery voltage dropping, the amplification on the receiver
grew giving a more consistent signal output level over the course of use.
The design of the amplification part of the receiver consumed very little current. The major loss
in efficiency came with the power supply mechanism. We needed to drive our output both
positive and negative, so we needed a dual-rail supply. We looked into voltage regulators, but
in the end didn’t find any that suited our low-power needs. We ended up using a simple voltage
divider with two 560Ω resistors in parallel with two 390µF capacitors. We started out using
10kΩ so the total current lost would be less than a milliamp, but found that there was too much
distortion as the positive and negative voltage rails fluctuated relative to the center tap
V+
ground
V-
(ground). At 9V, the resistors consume about 8 mA while the entire receiver consumes about
11-12mA. The total and relative current does drop as the battery’s voltage drops but it is still far
more power hungry than the op-amp.
12
System-Level Functionality
The system in its final configuration is capable of transmitting clean, undistorted music for up to
10 hours without recharging. As the transmitter supply voltage drops below 7.5 volts, the
music quality deteriorates due to the laser reaching its threshold level. Music ceases shortly
afterward at around 7.3 volts. Test results are as follows:
Transmitter Voltage
10.5
10
9.5
9
8.5
8
7.5
7
6.5
6
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5 10
Time (Hours)
Reciever Voltage
9.5
9
8.5
8
7.5
7
6.5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5 10
Time (Hours)
13
Identical experiments were run with end times of 9.5 hrs, 8.75 hrs, 3 hrs, and 10 hrs. Time
differences depend on the charge of the battery. The 3 hour test is likely from a ruined battery,
possibly from overcharging or draining the battery too low.
The receiver output signal strength is primarily a function of the laser alignment. Acceptable
signal levels range from 150 mVpp to 1.9 Vpp and are attainable at any distance up to 20 feet
(likely further, true maximum distance unknown).
Charging Circuit and LED Indicator
Through online research we discovered that there are very complex charging circuits that can
be built. These circuits include voltage detectors and many components that make them very
complicated. We also discovered that for NiCd batteries, the type we are using, as long as the
current into them while charging is never more than 1/10 the max current discharge then you
would never damage the battery no matter how long you charged it. The downside to this was
that it takes a long time to charge. For our battery we figured out that as long as we never
charged with a current greater than about 14 mA we would never damage the battery. We got
a 12V ac/dc adapter from the shop and put a 100 ohm resistor in series with it and the battery.
The measured current was always between 11.5 and 12.5 mA. This was a very simple, but
functional charging circuit. The charge time for this charging circuit is 14 hours.
One important part of the project is being able to know if you had a charged battery or not. We
designed a simple voltage divider that will illuminate an LED if the voltage on the battery is
above 9V. This is activated by the push-button on top of the webcam. We used the one that
was already there because we thought it would look better than adding another button. Also,
our LED indicator is the green one on the upper right hand corner of the webcam. The white
LEDs don’t do anything; they are just there for cosmetic reasons. Below is the diagram of our
simple charging circuit along with the LED indicator circuit.
14
Packaging
We were given the same-style USB webcams that were given to the groups last year. We
disassembled the webcams and removed the lense and circuit board mounted in the camera’s
“head.” We also removed the suction cup foot from the bottom. That circuit board was
replaced with one we cut out ourselves to the same dimensions as the old one. The majority of
our circuitry fit on that board (at least the same portion that was put in there by last-year’s
groups). Up to this point, there was no significant difference with regard to construction
compared to last-year’s groups.
After finding the appropriate container to use as a base, construction was relatively
straightforward. As for our specific construction design, we drilled a hole through the stem of
the webcam and fed wires through to connect the base with the upper circuitry. The
transmitter has 3 wires: V+, ground and signal. The receiver has 4: V+, V-, ground and signal.
The base was an Icebreakers breath-mint tin painted black for color coordination. It was
attached to the webcam using a couple of well-placed, hidden bolts. The battery is contained
within the base, but can be easily removed or replaced by opening the snapping-flap battery
cover. Also contained inside the base is circuitry for power. The charging circuit is there along
with an on/off switch mounted in a hole cut into the blue base of the webcam as well as a
couple of capacitors for noise suppression in the receiver with a single one in the transmitter.
For external ports, we got a RCA jack for the signal and a DC Jack for battery charging. The shop
doesn’t sell a surface-mountable DC jack, only one designed to be put on a breadboard so we
used a couple of lead wires and used shrink tubing to cover up the solder joints and a small
insert to clean up the hole where the wires come out.
15
Our group won Best in Show (or at least was the least hideous according to the secretary
judges). Our design was the smallest compared to the rest. Its dimensions also most
approximated the golden ratio, so perhaps that had something to do with it.
Lessons Learned
The first thing that we wish we had done better was keeping more detailed records. There
were several times when we wish that we had data that we previously had neglected to
record. We also wish we hadn’t burned out so many lasers throughout the semester. We
learned that they are extremely sensitive. They shouldn’t be driven higher than about 30mA,
any power supplies or even meters shouldn’t be turned on or off when connected (because of
voltage spikes). Care should be taken as well when touching the laser and in making sure other
circuit elements do not touch the laser.
Conclusion
We are happy that we are finished with this project and that it turned out so well. We learned
so much this semester. From the beginning of the semester several things have happened. We
learned a lot about teamwork, time management and ourselves. We learned about what it
takes to go from an idea that a “customer” wants all the way down to a working prototype
including design reviews along the way. The greatest thing we learned was that we could do it.
We gained a lot of confidence from completing this senior project. That is something that will
greatly help as we begin our first jobs shortly. We came to understand now more than ever
before what it means to rely on other people to accomplish a goal as we worked together as a
team to get our project working. There are a couple things that we would do differently if we
were to do it all again. One thing we would do differently would be to take more scrupulous
notes as we made decisions and changes to our design. Often times we would change our
design and ask if it was better than what we had before, only to find out that we didn’t record
data from the first simulation and so we’d have to do it over again. It would defiantly save time
to take more careful notes. Another thing we would change would be that we would be more
aware of the schedule as the semester moved along. We learned this about halfway through
the semester after missing our first couple major deadlines by weeks. When you are aware of
the schedule and the deadlines in it, there is a much greater motivation than not being aware
of deadlines. Basically things tend to get done on time when you know when they are
supposed to be done by. This is a seemingly obvious lesson, but when you experience it and
see the difference it will be easier to do in the future. We really enjoyed the fact that we were
able to see this project to completion from beginning to end. That is something you rarely see
as an undergrad and it was a great experience to have.
16
We were satisfied with our final design. We know that the receiver can last almost indefinitely
compared to the transmitter, and the transmitter can last about ten hours. That was long
enough to beat all the other groups in the competition. We also were voted the best looking
prototype as well, so we were the best in all aspects of the competition. We ran into many
bumps along the way, but once we got the receiver working with the single op-amp, and moved
the resistor from the collector to the emitter on the transmitter, it was all just tweaking the
design to optimize it. Moving everything from the breadboards into their final, soldered state
went smoothly and it all worked the very first time.
17
Concept Selection and Generation
Weight Single
Single op-amp in Dual-stage
transistor transimpedance op-amp
configuration
Power consumption
Adequate freq. response
Cost
Weighted Sum
40
50
10
9
5
5
100 660
6
7
5
4
8
4
640
600
Overview
The purpose of this document is to outline and quantify our most important design decision of
the project. Based on the experiences of previous groups which have done, we have
determined the receiver circuit portion of our design to be of the highest priority and
complexity. Many previous years designs had fancy transmitter design circuits, but all ended up
going with a simple single-transistor design for the final project. We believe there is wisdom in
their decision and will follow suite.
For our receiver design, we have considered several options. The simplest of these designs is to
have a single transistor to amplify the signal out of the photodiode. Another design option for
the receiver would be to use a single op-amp in a transimpedance configuration. This option is
one of the most popular designs from previous years. Another option that we considered is to
have a dual-stage op-amp configuration to give us better signal gain.
18
Decision Criteria Analysis
The decision criteria we chose for designing our overall circuit were extracted from our
customer needs. Our customer needs were determined previously in our functional
specification document and are listed in the following table. Their priority or importance has
been ranked with one being the highest or most important.
#
1
Priority
5
2
3
9
8
4
5
6
7
8
9
10
10
6
2
3
7
4
1
Customer Need
Sufficient laser alignment tolerance to ensure continuous device
operation during minor bumps. This will also make for a faster and
easier set up.
On/Off switch on receiver and transmitter.
Portable receiver and transmitter. All electronics and batteries
contained within the enclosure.
LED indicating when the battery is finished charging.
Low enough laser output power to be safe.
Music should be clear and distortion free.
Batteries should last for several hours.
Easy to plug in.
Laser and transmitter should remain aligned after adjusted.
Safe charging mechanism. Nothing should overheat or explode if left
plugged in.
Our customer needs as they apply to our fundamental circuit design can be grouped into 3
major areas: power consumption, frequency response, and cost. Customer needs numbers 4, 5
and 7 relate to having an efficient design with regards to power consumption. Need number 6,
music quality, directly translates to having a circuit with adequate frequency response. We
chose cost for our final decision making criteria because although it has little relating directly to
the customer’s needs as listed above, it puts an upper bound on how well we can practically
make all of the features of our product.
Some of the customer needs above we did not address in this particular decision making
process because they are irrelevant to our basic circuit structure. Many of these needs; such as
laser alignment, portability, switches, and LEDs do not relate to our choice of basic circuit
construction and therefore were not considered.
19
Weighting Factors
Many factors were considered as we decided on how much weight would be given to each
category, power consumption, frequency response, and cost. As can be seen above in the
prioritized needs chart from the FSD, frequency response was considered the most important
of the three, and thus it was given the highest weight. Frequency response is so important
because if the circuit we build has a longer rise/fall time than the actual DVD output then the
music will either sound very distorted, or even unrecognizable. We gave this category a weight
of 50. The second most important category was power consumption. We will only have a
single 9V batter on each end of our device. This single 9V battery must power each circuit for at
least 5 hours. This is also a very important requirement. If the music sounds good, but only last
for an hour or so we still are not meeting our specifications. This is why we gave power
consumption a weight of 40. It is a little less important than frequency response, but still very
important. The last category was cost. We know that none of these options will cost very
much and so there won’t be much difference in the cost. Our budget is such that we are not
worried about spending too much on a couple of circuit components and so cost was given a
weight of only 10.
Process Scoring Analysis
The process of assigning a score to each idea was quite interesting. We began by scoring each
in terms of their power consumption. We decided that a single transistor would be the best of
all so we gave it a score of 9. A single transistor will obviously use less power than an op-amp
which contains many transistors. A single op-amp stage would use more power, so we gave it a
score of 6, still less than two op-amps which we scored at 4 since two would use more power
than one.
We then scored each option based on the frequency response category. A single transistor can
be less stable which affects the frequency response, so we gave it a score of 5. The single opamp is significantly more stable and gives a better frequency response than a single transistor
so we gave it a score of 7. A two stage op-amp would be the most stable and best frequency
response of all, so we gave it a score of 8.
The category of cost was the last one used to rank the different ideas. A single transistor would
cost about the same as an op-amp so we gave them both scores of 5. Two op-amps would of
course be more expensive than one so that got a score of 4. Two would be a little more
expensive, but we still aren’t breaking the bank.
20
Review of the Results
This was a very interesting exercise for us. We really weren’t sure what the end result would
turn out to be. We knew that a single transistor would use less power, but we also knew that
the op-amp options would have better frequency responses. We just decided on weighting as
we thought it should go and gave honest scores in each category. In the end, the totals were
very close. The two stage op-amp design came in last with a score of 600. The single stage opamp came in a very close second with 640. But the single transistor won in the end with a score
of 660. We will follow these results and use a single transistor to power each circuit, but the
transmitter and the receiver.
21
Functional Specification Document
Project Description
Our free-space optical system is designed to transmit and receive a digital audio signal from a
DVD player to a Stereo amplifier across the room using inexpensive lasers. The product consists
of a transmitter and a receiver. This semester’s variation on the design is to make the system
able to run off a 9V battery. Because of this restriction, our focus is on making a design with as
low power consumption as is possible to maximize battery life and, as a result, operation time.
The battery will be integrated into the system such that it can be plugged into the wall to
charge. Our project should work at a variety of distances. We will test them specifically at 5ft.
and at 20ft.
This document serves as a guide to define our product specifications. Included are both the
nominal or minimum values we need to obtain as well as the ideal numbers that will serve as
our goals. We have also related these values to indicate how they fill our customer’s needs.
Block Diagram
22
Customer Needs
Customers who use this product will expect the following features and attributes. Their priority
or importance has been ranked with one being the highest or most important.
#
1
Priority
5
2
3
9
8
4
5
6
7
8
9
10
10
6
2
3
7
4
1
Customer Need
Sufficient laser alignment tolerance to ensure continuous device
operation during minor bumps. This will also make for a faster and
easier set up.
On/Off switch on receiver and transmitter.
Portable receiver and transmitter. All electronics and batteries
contained within the enclosure.
LED indicating when the battery is finished charging.
Low enough laser output power to be safe.
Music should be clear and distortion free.
Batteries should last for several hours.
Easy to plug in.
Laser and transmitter should remain aligned after adjusted.
Safe charging mechanism. Nothing should overheat or explode if left
plugged in.
Product Specifications
In order to know when we are finished with the design and testing of our free space optical
music transmission device we have developed a number of metrics as a guide. When these
requirements are met we will know that the project requirements will be met and we will not
need to improve upon the design any more.
Metric
#
1
Need #
Metric
Units
Marginal Ideal
Val
Val
4
6
6
Frequency Response
Mhz
2
7
Time the Transmitter run off a single charge
Hours
5
7
3
7
Time the Receiver run off a single charge
Hours
5
7
4
7
Average current used by Transmitter
mA
24
20
5
7
Average current used by Receiver
mA
24
20
6
3,7
Number of transistors used in Transmitter
Number
30
1
7
3,7
Number of transistors used in Receiver
Number
60
1
8
3
Width of battery base on each web cam
cm
10
7.5
9
3
Height of batter base on each web cam
cm
5
3
23
10
10,8
11
7
12
7
13
5
14
1,9
Time to charge the battery
Hours
16
14
Voltage levels at which the Transmitter
operates
Voltage levels at which the Receiver
operates
Laser must be safe for users
V
8-9
5-9.4
V
8-9
5-9.4
3
1
2
0
Laser movement
Laser
Class
mm/hour
The following will describe why each unit was chosen for each metric.
For metric one we used the used our measurements of the output of the DVD player. The
shortest signal we measured was at 4 Mhz so that automatically makes it our minimum value.
We chose 6 Mhz as the ideal value to add a 50% cushion to our measured value.
For metrics two and three we know that the circuit must operate for five hours, again, that
marginal value was given to us. We think that if we can get our devices to operate for 7 hours
we will win the competition, and so that is our ideal value.
Metrics four and five were chosen based on the spec sheet that Tenergy (the manufacturers of
our batteries) published. It claims that the battery can operate at 24mA for five hours. The
ideal value is the current we calculated we would need for seven hours.
Metrics six and seven were chosen because we know that the fewer transistors we use the less
power the circuits will consume. The ideal value for each would of course be one per circuit,
but we may need to use one op amp in the transmitter and up to two in the receiver. A single
op amp can contain about 30 transistors, so this is why 30 and 60 were chosen for the marginal
values.
The eighth and ninth metrics were chosen because we want the extension of the webcams to
be able to house the batteries, so it needs to be big enough for that, but not so big that it looks
awkward.
The tenth metric was chosen again based on the battery spec sheet. It recommended 16 hours
for a full charge, but indicated that it could be done in 14 hours with a little more current as you
charge.
Metrics 11 and 12 were chosen based on the battery spec sheet again. The chart indicates that
they operate nominally at 8.4 volts, but towards the end it is closer to 7. The fresh battery
outputs 9.4V in the beginning. Marginal operation would be between 8 and 9 volts. If we
included a voltage regulator a better range would be 5 to 9.4 volts.
24
Metric 13 was chosen because we want the laser to be safe. Lasers are always classified based
on the power they output. Class 3 are considered safe, so that is why it is our marginal value,
but class 1 would be even better and appear to be even more safe.
Metric 14 was chosen because ideally the laser would not move at all once operation begins.
Unfortunately it might, so based on the large spot size at 20 feet it would be able to move 2
mm every hour for five hours and still be on target.
Summary
We feel that we have established an accurate list of product characteristics that the customer
will expect. We have translated those needs into measurable and testable parameters that will
serve as our guide throughout the product development process. Comparing our final results
with our proposed goals will indicate the level of success of our final product.
25
Project Schedule
Measurements were obtained based on the following test schedule:
First Design Review
Simulated frequency response of the transmitter
Measured frequency response of the transmitter
Measured power consumption of the transmitter
Measured power density at 5 feet and 20 feet (W/cm2)
Second Design Review
Simulated frequency response of the receiver
Measured frequency response of the receiver
Measured power consumption of the receiver
Measured minimum detectable power of the receiver
Voltage range of the commercial receiver box
Find any standards related digital audio transmission protocols. (i.e. what is the DVD using)
Distance range over which the system will transmit music
Final Demonstration
Eye safety class on the device
Documented eye safety requirements and specifications
Measured alignment sensitivity
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Blazer Designs LLC
Battery-Powered FreeSpace Optical Digital-Audio
Transmission System
Operating Instructions
Model
SDN-001
©2010 Blazer Designs LLC
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WARNING Class 2 laser device
!
Do not stare directly into beam
Connections Overview
Transmitter
Receiver
DC in
DC in
Digital in
Top
Digital out
Battery Test Button
Front
LED Battery Indicator
Laser
Photodiode
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Setup Guide
Digital-audio source
(CD/DVD player or
other device with
S/PDIF out)
Digital-audio receiver
with S/PDIF in
1. Charge batteries by using the supplied wall plug adapter.
Be sure that the on/off switch is in the off position.
2. After charging, disconnect the AC Charging adapter. You
may press the button on top to ensure that the battery is
fully charged. If the green LED is dim the battery is not
fully charged.
3. Connect the digital port on the transmitter to a digital
audio source and the laser receiver to digital receiver or
digital-to-analog converter (DAC)
4. Aim the laser in the transmitter at the photodiode in the
receiver. This can be done most easily by turning on both
the digital audio source and the amplifier/receiver and
both the laser transmitter and receiver units then listen
to the output of the amplifier and adjusting the alignment
until clear noise-free sound can be heard.
To ensure a long battery lifespan, do not run in excess of 9
hrs. between charges as the battery may be damaged when
overly deeply discharged
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Specifications
Frequency Response
3dB
4MHz
Transmitter current
17mA @9V
Receiver Current
13mA@9V
Vertical alignment
tolerance
0.12°
Horizontal alignment
tolerance
0.12°
Operating distance
Up to 20 ft.
DC in
+
-
12mA @12V
Laser power output
<1mW
Laser Class
2
Receiver Gain
36700 V/A
Output signal level Vpp 800mV
Signal output noise
>50mV
Battery capacity
2700mWHr
9V NiCd
Charge time
14 Hrs.
Min. operating voltage
Tx: 7.3 V
Rx: 3 V
Dimensions
7.5x7.5x12
cm
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