By

Jeff Patrick

Advisor: Alexander Malinowski

The Networked Home Theater is a hardware interface and software to connect any Sony CD player to a network. The hardware interface will consist of a microprocessor to control communications between the CD player and a host PC. The software will be two separate programs, a Java server and an Applet.

The server will communicate with the microprocessor and the Applet to moderate communications. It will also connect to CDDB, an Internet CD information database, to retrieve information about the current CD.

The applet is the front end of the project, and will be what the end user uses. The applet will display status pertaining to the current CD, information retrieved from CDDB, and controls for the CD player.

Most Sony home theater components have a built in communications protocol. The various components connect to each other through a S-Link port. S-Link is a two-wire serial data bus that provides two way communications. Sony’s intent for this bus was to allow their components to interact and allow an easier and more fun home theater experience.

The Networked Home Theater project connects the S-Link bus to a PC (Personal Computer). The PC has the opportunities for advanced automation of the components. The PC will be able to control the CD player as well as read information from the player. A Java server on the PC will allow Java applets on the Internet to connect and remotely control the player. The server will also download the CD information from CDDB.com.

Figure 1 The block diagram of the networked Sony system connected to a personal computer connected to the home Intranet or to the Internet.

Figure 1 shows the block diagram of the entire system. The Sony CD player will connect directly to a microcontroller through the S-Link connection. The microcontroller will control communications directly to the CD player.

The microcontroller will then be connected to a PC running a Java server. The connection will be made through either a serial or parallel port. The microcontroller and PC will communicate to each other through a proprietary protocol that is not yet developed.

The Java server will manage several tasks. First, it will connect to the CDDB online database and retrieve the information about the currently playing CD (title and track contents.) Access to the CDDB database is available through a proprietary library available in C language for Windows platform. The Java language allows C functions to be called within the Java code. The server will also communicate with Java applets that will connect either locally or over the Internet. The applets will be the front end of the Networked Home Theater system. The end user will be able to send the server commands, which in turn will send the commands to the microcontroller, and ultimately, the CD player.

The Other Components Block could be other Sony products, such as DVD players or receivers. It could also be another brand of control signal if it exists.

The system is in an idle state while it is waiting for a client to connect to the server and control the unit (Remote Control Mode) and listens to activity on the S-Link bus. In the case of playing a new CD, the mode switches to Query mode.

The system is being controlled by a remote user. The user sends input through the system, and the system sends back status information to the user. When a user plays a CD the system temporarily switches to the Query mode so that the CD information may be retrieved. The current command set is listed in Table 1 below:

Table 1 Current instructions to be made available to a remote user of the system.

The CD player reports the CD identification number to the PC. The PC then retrieves the CD information from the CDDB database. The information of each CD will be stored in a local database to allow selection of any CD in the player and to prevent the necessity of multiple inquiries about the same CD in the future. After obtaining the information the system returns to the mode previously active.

In order to connect the CD player to the PC, several factors must be taken into consideration. The CD player outputs TTL (0-5) voltages, while the serial port on the PC outputs RS232 (-15 – 15) voltages. Some voltage conversion must be done in order to connect the two.

Second, the CD player communicates at a 600-microsecond time base. The Java server has a minimum wait time of 1 millisecond. In order to communicate at the speed required, the communications functions must be written in a separate language. In addition, the server PC will be slowed down considerably by the need to monitor a port at high speeds. This is a very large waste of processor power since the S-Link bus is unused 99% of the time.

To reduce strain on the PC processor, and reduce the complexity of the server software, a microprocessor will interface the PC to the CD player. The microprocessor has the ability to communicate to the CD player at a 600 microsecond base frequency. It can then talk to the PC at a slower speed. The microprocessor will also take care of the voltage conversions between TTL and RS232. Figure 1 shows the block diagram of the entire system with the microprocessor interface. In addition to controlling just Sony devices, the microprocessor will have the capability to talk to different bus’s if the need arises.

The microprocessor code is very simple. Figure 2 shows the entire microprocessor code flowchart. The majority of the time the processor will be in an idle state. While in the idle state it will listen to both the Serial and the S-Link bus. When it detects information on either bus, it will convert it into the format of the other bus and send it. If the ability to interface multiple buses is implemented, the microprocessor will also analyze the incoming signal and route it accordingly.

Figure 3 Server Code Flow Chart

The Java server has several functions, which are shown in figure 3. The first operation of the server is to wait for a connection from an applet. Once a client is connected, the server will transmit status information about the system. After the status information is sent the server will wait for an instruction from the client. When an instruction is received, the server will pass the command to the microprocessor through the Serial Port Out. Finally, the server will return to the Wait for Instruction mode.

The server will also be running a separate thread to detect if any information is being sent from the microprocessor. When status information is received from the processor, the server will analyze weather the information is a CD identification number. If so, the server will connect to CDDB using proprietary libraries from Gracenote/CDDB. If the data is not a CD identification number, the server will skip the CDDB connection step. The code then enters a Report Status block. This block parses the data received from the processor or from CDDB.com and prepares it for display. Finally, the data to be displayed will be sent to an applet through the Socket Out block.

Figure 4 Chat Server Block Diagram.

A second server will be running to manage the chat functions. If a second user tries to connect, he will not be able to control the CD player, but he will be able to chat. The user controlling the CD player will be using both flowcharts to control and to chat. Figure 4 shows the server flowchart when a user connects. First the user is added to the list of connected users. Next, the server will wait for new data to be transmitted. If a user connects, the updated list of users is considered new Data, and the server will go to the next step. All the data will be broadcast to all users. This data includes the user list, CD info, and any new chat data from the users.

Figure 5 Applet Code Block Diagram

Figure 5 is the flowchart for the Applet. The applet will connect to the server and split into two threads. The thread on the left waits for data to be sent from the server. When the applet receives data (either chat or status data) it will display it for the user of the applet. The thread on the right waits for data to be input by the user. Once the user sends a command or types in the chat the applet sends the data to the server. The server will then send a reply to the applet with either the chat info or updated status on the CD player.