2. DESIGN REQUIREMENTS The device developed in this project will incorporate sensors and a camera into a single package that will communicate by Ethernet. Multiple devices may be connected to a single computer to allow data to be collected and stored in a single location. On-device storage will accommodate data when no computer is connected or the network is unavailable. The successful application of the developed device will depend on fulfilling certain requirements that effectively guarantee a minimum functionality. The technical and practical constraints will each effect a more attractive product, but from two different perspectives. The technical objectives will enhance the capability of the device. On the other hand, the practical constraints will enable the purchase by an end user, by assuring levels of safety, quality, and cost. 2.1. Technical Design Constraints Table 1 lists the technical design constraints of the device. These constraints ensure that a workable solution to the problem will be developed, and the resulting device will be able to function in the needed capacity. The full operation, from sensors to the connected computer, is covered by the fundamental sequence of requirements outlined in this section: a common camera interface, a sufficient storage capability and noise level, a flexible and quality compression, and a user interface in a familiar environment. Name Description Storage Can store 1 hour of data Camera Protocol Will connect to IEEE-1394 IIDC-compatible camera Compression MPEG-1 video compression will be used Noise The device will have a noise level less than 20 dB Software Compatibility The software will be Windows-compatible. Table 1. Technical Design Constraints 2.1.1. Storage The device will have the capacity to store one hour of data; this data includes the video and audio recordings and the EMF, temperature, and motion sensor values. This storage will allow the device to record during sustained periods of activity without relying on a connection to a computer. The operation of the device and quality of output will not rely on a favorable network load (or even the immediate presence of a network or computer), and the flexibility of the system will be increased. 2.1.2. Camera Protocol IEEE-1394, also known as Firewire and iLink, is rapidly becoming a choice communications bus for device access from a computer. The IIDC (Instrumentation and Industrial Digital Camera) specification, also referred to as DCAM, is a standardized protocol for uncompressed video transfer over Firewire. This standard was developed by the IEEE 1394 trade association to specify a consistent camera interface for data transfer and camera control. Most video recorders that connect through Firewire and are IIDC-compatible will be able to provide video for the device. A large number of inexpensive cameras are included in this profile, such as many popular webcams. Open Host Controller Interface (OHCI) provides a standard for device access by an operating system. For the embedded device software, an OHCI-compatible camera will ensure plug-and-play operation; consequently, the user will be able to plug in an IIDC camera during any software state, and the software will recognize and use the new device. If the user does not employ an OHCI camera, he/she may need torestart the system in order for the software to recognize the presence of the camera. 2.1.3 Compression The camera will record 30 frames per second at 640 x 480 resolution with 24-bit color; consequently a calculation can be performed to estimate necessary storage for uncompressed video: GBhrssframepixelbytesrowpixelframerow6.993600*30*3*480*640 = Consequently, fulfilling the first technical design constraint, which dictates a minimum storage of one hour of data, necessitates some form of video compression. The video and audio streams will be compressed using the MPEG-1 standard, with layer 2 encoding for the audio. This choice has several implications: 1. A compression ratio of 124 is produced compared to the raw camera output. A 10 GB hard disk will be able to hold 16 hours of video rather than 6 minutes, allowing a smaller drive to be used for this application. 2. This format is supported by the VCD standard which allows 80 minutes of video to be burned on a single compact disc. The user will easily be able to produce media playable in many DVD players with CD-quality sound and VHS-quality video. 3. The user will not access the data on the device itself, but on a computer that is connected via a 10/100 Base-T Ethernet link. Transferring the raw video would be time-consuming and would make an excessive demand on the network. The MPEG-1 video has a sufficiently low bitrate to allow reasonable transfer times. 2.1.4. Noise Level The ability of the connected microphone to detect noise from the surroundings depends on the noise of the device itself. The design of the device will consider the resultant noise level by incorporating a fanless processor and relying on an AC/DC converter rather than a traditional computer power supply. The goal is to create a device that generates a sound level below 20 dB, which is equivalent to a whisper heard from 5 feet. This will not generate enough background noise to affect the recordings. 2.1.5. Software Compatibility The software that allows the user to manage connected activity recording devices will run under a Windows operating system. Full compatibility will be guaranteed only for versions Windows 98 and later (Windows ME, 2000, and XP). These operating systems enjoy widespread usage, and the computers of most users will probably run a Windows version and be familiar with this installation. Windows Media Player 9 will be required for the program to function fully; consequently, the user will be prompted to visit the Microsoft website to download Media Player if it is not already installed. 2.2. Practical Design Constraints The practical design constraints are shown in Table 2. Whereas the five technical constraints are measurable abilities of the device, the practical considerations below essentially include the measurable conformances of the device. The safety constraint attaches a recognizable and desirable UL conformance to the device. The economic, manufacturability, and sustainability requirements deal not with a predicatedstandard, but with conformance to user expectation. Altogether, these constraints will help ensure