My work on the design document so far

Engineering Tools

What engineering tools have you used and do you expect to use in order to design and implement your project? Describe both software tools (compilers, debuggers, etc.) and hardware tools (logic analyzers, multimeters, etc.).

We will use text editing software such as Textpad or Notepad++ to write our code. To compile, we will use the Keil C cross-compiler for the 8051 microcontroller. For testing, we have debugging software (say what this is) which works with a hardware 8051 emulator (say what this is) to help us develop our software. The lab we are working in has Dell PCs, variable power supplies, and digital multimeters. The lab does not have any oscilloscopes or logic analyzers.

Standards

What standards (commercial, industry, international, etc.) did you decide to use and why? What other standards did you consider and discard and why? In what ways will the use of standards influence your project.

We will use the Zigbee wireless communications standard, because it fits our project's needs fairly well. Zigbee is designed for use with embedded systems, and it is meant for creating mesh networks. One downside of Zigbee is that it provides relatively low bandwidth. In our research, we considered using the 802.11 wireless standards, but we decided not to use them because they are not meant for mesh networking. The use of an existing standard will save us a lot of time and work, because we don't need to develop our own wireless mesh networking protocol. Because of the existence of Zigbee devices, all we have to do is buy some Zigbee radio chips and figure out how to interface with them.

System Architecture:

This section should present the high level structural design of the system. This section should describe how you arrived at the structure and what tradeoffs you explored.

System Architecture contents should include:
System Architecture Diagram
Functional Analysis and Requirements
Functional Description of Each Component
Subsystem/Component Alternative Generation and Trade-offs (for several of the most important design features)
Systems Engineering analyses pertaining to issues such as power/weight/error budgets, etc.
Experimental Analysis – Did you perform experiments to evaluate feasibility?

The main components of our project are a battery pack, an 8051 microcontroller, an XBee Zigbee radio chip, an analog-to-digital converter, and a digital-to-analog converter. Each unit will have an analog input, an analog output, and a power switch.

We decided to use the 8051 as our microcontroller because two of our group members have prior experience working with 8051s. We felt the microcontroller would be more than adequate for our needs. The model we will use has a fair amount of memory, is reasonably powerful, and does not cost very much. It is available in dual-inline-package, which makes it possible for us to prototype our project with breadboards. We wanted to get an 8051 that would have onboard ADCs and DACs, and possibly even an MP3 encoder/decoder, but such an 8051 is only available in a surface mount package that would be impossible to use for prototyping. It would have been useful for our 8051s to be in-system-programmable, but such chips are more expensive.

We chose the XBee Series 2 radio because it is a reasonably priced radio chip that does what we need. It is capable of forming mesh networks if it is set up correctly, using the Zigbee wireless protocol. The XBee has pretty good documentation, and the company that sells it has good support available. The XBee does not use much power, so it should be possible to keep it running for several hours. We considered some cheaper Zigbee chips, but they had far less features and would have been much harder to use. The XBee has a simple serial interface and is programmable, which means that using it should be relatively easy.

We will use batteries to power our project because it is meant to be a small, mobile unit, and so it would not be possible to run it off a permanent power source.

We will start by testing just two XBees to see if they work the way we want them to. If they do work, we will order more. To make sure the Zigbee protocol really does what we need, we researched how it actually works.