Wireless display device

Introduction:

The conference room scheduling project provides a web interface for scheduling times for the conference rooms in Bourns’ College of Engineering. The user can select any date up to 11 months in advance and reserve a time for the rooms. After selecting a time, a circuit consisting mainly of a transmitter will send the new information to the conference rooms periodically throughout the day, so that the room can display the schedule on an LCD. The LCD’s for each room will rotate the schedule for each half-hour increment of the current day.

Implementation:

The receiver circuit consists mainly of an 8051 microcontroller and a receiver. When the circuit is not receiving data, it will rotate all data for each half-hour increment of the current day on the LCD. If new data is sent, a serial interrupt will occur causing the circuit to stop rotating and start receiving. This data is then stored and the circuit goes back to rotating the text.

Communication Protocol:

The communication protocol was designed so that if a certain packet (BEGIN_TRANSMISSION) is received, the circuit would automatically interrupt and start receiving. In order to ignore data that is sent more than once, another packet called (SAME_TRANSMISSION) is sent. This will not interrupt the circuit unless an error occurred on the previous send. Each time data is sent, it is divided into groups for each half-hour increment. Therefore, a BEGIN_TRANSMISSION or SAME_TRANSMISSION will be sent for each time slot. This allows the circuit to avoid having to read in data for each time slot if only one or a few times have changed. Also, if an error in one time slot occurs, it will be corrected on the next send without having to change any of the other times. The protocol uses NRZ encoding and transmits and receives at 2400 bits per second.

The transmitter circuit connects to the serial port of a PC in order to transmit the data from the web. The PC is constantly running a monitoring program that will check the data for each room at specific time intervals and re-send it. The transmitter was originally designed to run on the power of the serial port, but some computers do not provide enough power so the circuit must be powered manually.

The web-based scheduler consists of 2 CGI’s written in PERL, some simple HTML, and JavaScript. The opening screen asks the user for the month, day, and room that they would like to sign up for. After clicking OK, the first CGI is called which dynamically builds a web page for that day’s schedule based on what is already stored in a file. The scheduler is protected from concurrent access by using file locking. The user can then sign up for any time on that day by clicking a button. The second CGI is then called, causing the updated information from that day to be written back to file. The transmitter circuit later transmits the data.

In order to send the data from the scheduler to the receivers at each room, a Windows program is required. The program reads in the files for each room at specified intervals and sends the data through the serial port to the transmitter. This program was written with MFC using Microsoft Visual Studio 97.