ECE 345 Project Proposal Stefan Mahlknecht and Michael Brown Submitted 2/17/1999 Laser Modem Abstract: 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
"Project Proposal Computer Laboratory - DOC"