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Project Proposal Computer Laboratory - DOC


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									      ECE 345 Project Proposal
Stefan Mahlknecht and Michael Brown
        Submitted 2/17/1999

          Laser Modem

        The intended function of this system is to provide a wireless optical communications link
between two computer systems. The modem will communicate at 115kbps. The modem will
attach to a computer through a standard RS-232 COM port. After initialization the connection
will be transparent to the user. Our project may involve the use of basic optics to increase the
transmission range.
        This project should be interesting to anyone with an interest in computers. Complicated
hardware is often difficult or time consuming to initialize. Our laser modem will be free from
these concerns. It will be easy to hook up because it will simply plug into a serial port. It will be
easy to use because initialization requires only double clicking our initialization program before
using hyperterminal. And our project will be convenient because no path between sender and
receiver will be needed other than free space.

Project Goals:

         We intend to demonstrate a working pair of modems. The distance the modems will
communicate across will be at least the distance of the laboratory. We would like to increase this
distance to 100m or so depending on our success in getting the proper optical components and
mountings. Further, after initialization of our modem, we will require no further software
control of the modem. This will enable the modem to be connected to a computer’s serial port,
initialized, and used as a null modem link through existing software. This will eliminate a great
deal of effort to correct errors in our signal (due to fog, rain, birds, etc.). We would like to attain
the maximum communications rate possible for this circuit. In this case, the serial port and our
IC are limited to 115kbps transfer, we would like to achieve communications at this rate.
Depending on our progress, we may implement a hardware based initialization method to avoid
any need for software to initialize the modem.

Laser Modem Block Diagram:

        The block diagram works as follows: receive and transmit signals from the computer are
sent to the line receiver and from the line driver on the modem unit. The function of these blocks
is to convert the computer’s +12/-12 V signals into the 0/5 V range needed for communication
with the transceiver (and vice versa). We will construct this using a few transistors, resistors and
capacitors. Once these signals are in the voltage range, we can communicate with our
transceiver (a Crystal Semiconductor CS 8130 IC). The IC will modulate/demodulate our
signals based on a baud rate generated by an external crystal. If we are receiving, we can
directly connect our photodiode to some leads on the IC. If we are sending, we also have some
external circuitry to provide the power necessary to communicate in a variety of conditions.
        The voltage regulator will provide a steady 5 V power supply to our circuit, needed by
the IC and our laser diode driver. The control unit is used to send signals to the IC. Our IC is
configurable, and will require some control signaling to perform correctly. Initially, we may
implement some of this control in software to simplify our initial design task, but we would like
to implement hardware control to make this unit less dependent on software.

        As far as testing our project, our primary criterion will be a working modem. We will
verify that our modem is communicating at a given speed through our modem software. Other
than this, we would like to make the modem power efficient by making use of the transceiver’s
power down mode during idle times. We might make use of HP VEE for data acquisition and
plotting. We will try to test either or both of: power consumption and transfer rate.

         Due to our busy schedules late in the semester, we would like to get as early a start as
possible. We would like to focus most of our work early and have a pair of modems
communicating across the lab (at possibly less than 115kbps) by the week of March 15th. The
next few weeks will be very busy for us, and after our design criterion are met, we will try to
improve speed and distance. We would also like a hardware initialization method, and we would
like to etch our design on a printed circuit board. This would be the focus of the next few weeks
until project demonstrations and reports are due.
Nonstandard Parts List:                                Quantity        Estimated Unit Cost

Crystal Semiconductor CS 8130-CP Integrated Circuit.      (2)                 $7.50

Laser Diode (Hitachi 670nm HL 6720G)                      (2)                 $11.00

3.6864 MHz Crystal                                        (2)                 $2.50

photodiode (sensitive to 670nm range)                     (2)                 $1.00

Maxim 562 Communications IC                               (2)                 $6.00

serial cable                                              (2)                 $3.00

                                                Total estimated parts cost:   $62.00

(we’re not just designers, we’re consultants)   100 hours Labor @ $100/hr $10,000
                                                             x2.5         $25,000

                                                Total Cost:                   $25,062

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