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group3:group3final 2008/12/08 21:09 group3:group3final 2008/12/09 01:15 current
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===== 3.Final Design ===== ===== 3.Final Design =====
-This description refers to the design as it was actually completed and not as it was originally conceived; hence, final design.  The free-space optical system designed by Group 3 is a computer-to-computer system.  This allows for the user interface to be handled by the computers, simplifying design and allowing for better integration with existing hardware.  After all, most people own a computer.  The final design has three basic components: an optical transmission channel to send data over, transceiver electronics to convert between electrical data and optical signals, terminal software used by the computer to control the communication system, and the mechanical assembly on which the components are mounted.  Each section will be discussed in detail.+This description refers to the design as it was actually completed and not as it was originally conceived; hence, final design.  The free-space optical system designed by Group 3 is a computer-to-computer system.  This allows for the user interface to be handled by the computers, simplifying design and allowing for better integration with existing hardware.  After all, most people own a computer.  The final design has four basic components: an optical transmission channel to send data over, transceiver electronics to convert between electrical data and optical signals, terminal software used by the computer to control the communication system, and the mechanical assembly on which the components are mounted.
==== Optical Design ==== ==== Optical Design ====
The optical communication channel is very simple, since this is intended to be a short-range free-space optics system, and is almost identical in its final form to the original design.  As this is only a demonstration system, it operates in a half-duplex mode.  This means that the communication channel is one-way: one end can only send data, and the other can only receive.  As such, only one receiver and one transmitter were needed. The optical communication channel is very simple, since this is intended to be a short-range free-space optics system, and is almost identical in its final form to the original design.  As this is only a demonstration system, it operates in a half-duplex mode.  This means that the communication channel is one-way: one end can only send data, and the other can only receive.  As such, only one receiver and one transmitter were needed.
-An ordinary "dollar variety" 650 nm red diode laser pointer is used as a transistor.  This laser was chosen for its low cost, easy availability, and design simplicity.  The red wavelength is also less strongly absorbed by the atmosphere than shorter wavelengths.  The use of a laser also simplifies the optics of the transmission channel.  If the design had used an LED source instead, collimating optics would have been required to shape the output into a focused beam capable of traversing a long distance.+An ordinary "dollar variety" 650 nm red diode laser pointer is used as a transmitter.  This laser was chosen for its low cost, easy availability, and design simplicity.  The red wavelength is also less strongly absorbed by the atmosphere than shorter wavelengths.  The use of a laser also simplifies the optics of the transmission channel.  If the design had used an LED source instead, collimating optics would have been required to shape the output into a focused beam capable of traversing a long distance.
Unfortunately, this type of laser pointer suffers from reliability issues as well as highly variable beam quality.  A large number of backup and replacement lasers were purchased against the possibility of laser diode failure.  In order to simplify alignment, and account for the poor quality (high divergence) of some of the laser beams, a basic positive lens was used to focus the light onto the photosensor.  The lens selected was a "dollar variety" magnifying glass.  This lens was selected due to its low cost, fairly large area, and easy availability.  The photosensor is located at the focal point of this lens, which was experimentally determined to be approximately 34 cm from its center.  The lens then directs a laser beam entering at a normal incidence to any portion of its surface onto the photosensor. Unfortunately, this type of laser pointer suffers from reliability issues as well as highly variable beam quality.  A large number of backup and replacement lasers were purchased against the possibility of laser diode failure.  In order to simplify alignment, and account for the poor quality (high divergence) of some of the laser beams, a basic positive lens was used to focus the light onto the photosensor.  The lens selected was a "dollar variety" magnifying glass.  This lens was selected due to its low cost, fairly large area, and easy availability.  The photosensor is located at the focal point of this lens, which was experimentally determined to be approximately 34 cm from its center.  The lens then directs a laser beam entering at a normal incidence to any portion of its surface onto the photosensor.
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===== 5.Completed Product ===== ===== 5.Completed Product =====
-The completed product can be seen below, or, in more detail, in the photos above.  The parts list for components used is contained in the budget list. The important and critical devices involved include the laser, the p channel MOSFET, the computers with serial cables, the Mounting and aligning equiptment, the Tube and filter for noise reduction, the lens for focusing the light, the AC filter for signal isolation, the Comparator for Analog to Digital conversion, and the Inverter for inverting the signal. The total cost for construction is a theoretical $63.90. +The completed product can be seen below, or, in more detail, in the photos above.  The parts list for components used is contained in the budget list. The important and critical devices involved include the laser, batteries to supply power, the p channel MOSFET, the computers with serial cables, the Mounting and aligning equipment, the Tube and filter for noise reduction, the lens for focusing the light, the AC filter for signal isolation, the Comparator for Analog to Digital conversion, and the Inverter for inverting the signal. The total cost for construction is a theoretical $63.90. 
{{:group3:dsc00042.jpg?800x600|}} {{:group3:dsc00042.jpg?800x600|}}
 +
 +Close-ups of some of the components are shown below.
==== Transmit Circuit ==== ==== Transmit Circuit ====
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===== 6.Demonstration and Evaluation ===== ===== 6.Demonstration and Evaluation =====
The Demonstration and Evaluation of the project was done over two testing days. The first was an indoors test, and the second was an outdoors test. On both days, the test was a complete success. For the indoor test, the alignment was fast and the project worked right away and only malfunctioned when people walked across the beam during transmission of a file. When this occurred, the photo sent would contain Grey rows where information was lost. For the outdoors test, the alignment was more difficult due to low temperature conditions. The beam spot was also difficult to see due to the failure of 2 lasers the day before the test and the use of a high divergence laser on the day of testing. Nevertheless, the alignment was completed and the project worked again despite the higher amount of background light. This proved that the tube and the red filter were sufficient for blocking light. The Demonstration and Evaluation of the project was done over two testing days. The first was an indoors test, and the second was an outdoors test. On both days, the test was a complete success. For the indoor test, the alignment was fast and the project worked right away and only malfunctioned when people walked across the beam during transmission of a file. When this occurred, the photo sent would contain Grey rows where information was lost. For the outdoors test, the alignment was more difficult due to low temperature conditions. The beam spot was also difficult to see due to the failure of 2 lasers the day before the test and the use of a high divergence laser on the day of testing. Nevertheless, the alignment was completed and the project worked again despite the higher amount of background light. This proved that the tube and the red filter were sufficient for blocking light.
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===== 7.Budget ===== ===== 7.Budget =====
Parts purchased for the project: Parts purchased for the project:
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{{:group3:group_3_budget_2.jpg|}} {{:group3:group_3_budget_2.jpg|}}
-Total Cost: $134.64+Additionally, there was a shipping cost of $2.67 for the Digikey order, and a shipping cost of $4.00 for the Newark order. Therefore, the total cost of the project would then be: 
 + 
 +**Total Cost: $141.31** 
 + 
 +The cost to construct the system is a different matter, where only the parts used are included. Essentially the figure is an estimation of the cost to reconstruct the system on a mass scale. Also, shipping costs from Digikey and Newark would not be included, since many sets of parts could be purchased at the same shipping cost.
-Cost to Construct: $63.90+**Cost to Construct: $63.90**

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