Ubiquitous Computing Project, Phase III

Lukas Dudkowski
Columbia University
New York, NY
USA

Research Advisor,
Prof. Henning Schulzrinne
Columbia University
New York, NY
USA

Abstract

This report summarizes the continuation of the wearable computing/location tracking project. Development of the "tag" PCB is presented, with a goal of limited-run manufacture for possible deployment.

Introduction

This semester the main focus of my research has been the development of the Printed Circuit Board for the wearable tag. Whereas the main component design and testing occurred during phase II of the project, phase III has been the integration of the highly customized tag v2 design onto a PCB layout, as well as the further integration of additional functionality. Interface buttons, thumb-wheel control (for possible X-10 lighting level adjustment), and an integrated 7-segment display were features found desirable after examining the results of the phase II v2 tag.

Though the ultimate goal of phase III was the small-scale production run of the tag PCB, and possibly limited deployment, time constraints did not allow for the full completion of these goals. However, as of this writing, the tag is ready for a prototype PCB run. The 24TBA enclosure has been partly modified to accept the tag PCB, and the project can be continued with the deployment goal in mind.

For full project development history see:

Related Work

Background

For a full project account (previous phases, detailed design specs, etc) please see the previous project documentation from [1] Spring 2002, and [2] Fall 2003.

Problems Encountered

The design of a custom PCB which is suitable for a wearable computing application such as the tag is not easy. The components selected must be mated with the enclosure chosen for its small size and ability to accommodate the internals. My limited experience with PCB layout was the major problem encountered during this project. Despite repeated attempts, I was not able to find an individual in the EE/CS Dept who had any working knowledge of simple PCB layout. My initial attempts to design the PCB were met with failure due to my lack of experience both with general PCB layout concept as well as the Eagle editor. The trial-and-error methodology prevailed in this phase, and eventually yielded a final design. Though I was successful in the eventual design of PCB, a lot of development time was wasted in using this approach.

The necessity of using off-the-shelf parts forced me to choose an enclosure that was both cost efficient, as well as capable of meeting the technical requirements of housing the tag internals. Though the 24TBA enclosure has a belt-clip and accommodates the internals, its size makes it not an ideal enclosure for the envisioned applications. As seen above, the v3 tag, with the 24TBA enclosure, is significantly larger than the v2 custom enclosure, and adds only limited functionality to the overall design. This problem, however, cannot easily be resolved as the need for any significant number of tags would mean customization is out of the question.

Architecture Overview

The general architecture of the tag is outlined in the phase II documentation linked above. This phase of the project was mainly directed at making the PCB design, as well as the enclosure selected suitable for a limited production run. No major architectural changes were made, though functionality was added to the previous tag design through the addition of the display, I/O buttons, thumb-wheel, and new casing.

The enclosure choice was made with the goal of an easily obtained, wearable, and small size enclosure that fit the technical spec of the PCB board. Below you can see the enclosure with the added DB9 port, as well as attachable belt-clip. The enclosure is fitted with a battery access panel which accommodates the desired rechargeable 9v battery. Mounted on the top of the enclosure is the on/off switch, a feature absent from all previous versions of the tag. Enclosure and Hardware:

v3 enclosure as compared to custom enclosure from v2 of the tag

 exploded view, v3 enclosure

v3 enclosure with belt-clip and hardware

v3 enclosure with attached belt-clip

size comparison, v2 vs. v3 tag

Technical Information

The design of the PCB involves two files within the Eagle editor. First, the schematic file. In this file, the user places library components (those desired to be on the PCB) and draws connections according to the general circuit design using lines, or simple connections of that type. This schematic file is representative of the components that will be placed onto the PCB, as well as the traces that will be routed by Eagle's auto-router.

The second file, the *.brd file, involves the physical layout of the board. Here the size of the PCB is defined using a GUI interface, and components (read from the schematic file) are placed according to the desired orientation on the PCB surface. Pin-out connections and routes are read from the schematic file, and are represented by simple lines before the auto-router has been run. Once a desired orientation for the surface mounted components has been selected, the auto-router can be run to optimize the trace paths. In this way, the user can specify whether the PCB should be multi-layer, what kinds of traces (width, orientation, pad size, etc) should be used. Eagle's auto-router is surprisingly effective in optimizing the traces, and allows the user a great deal of flexibility in where the surface mounted components should be placed.

Here, we can see the chaotic schematic file, as well as the resulting *.brd file from that schematic.

Eagle System Schematic

Eagle Board Level Layout

Manufacture

The generated design file (*.brd) is suitable for manufacture. One would submit this to the PCB manufacturer directly, and have a production PCB run from this design. For a manufacturer that supports Eagle Editor files, see PCBExpress. This manufacturer will take the brd file, and generate all the required gerber and drill data.

Development Environment

Cadsoft, EAGLE Light Edition

  • CADSOFT ONLINE, source of downloads, tutorials, reference for the use of the Eagle Editor.

    The Eagle Light Edition layout editor is a free-ware version of the more powerful Eagle layout editor from the Cadsoft company. It is a one of the more readily available and easy to use PCB layout tools available to the hobbyist or novice user. It comes with an extensive library of built-in components available for placement on the project PCB, and allows for the importation of additional libraries where necessary.

    Limitations:

    The following limitations apply to the EAGLE Light Edition in general:

    What is new in v3 of the tag?

    Buttons Interface Schematic:[3]

    Thumb-wheel Pot Interface Schematic:[3]

    7-segment display and driver[4]

    Project Documentation

    Eagle Editor Files

  • Board file
  • Schematic file

    Tag Component Data Sheets

    Previous PPT presentations

    Summary and Future Work

    Though the design of the PCB has been completed, time constraints did not permit me to complete the manufacture and deployment phases of the project. The initial work on the prototype machining of the enclosure has also begun, with the mounting of the DB9 serial port, as well as on/off button. If this project is continued in the near future, the manufacture of the prototype PCB will allow of the mating of the internal components to the enclosure. Though the initial enclosure has to be machined by hand, as well as mated with the internal tag PCB components, future machining can then be handed off to the enclosure manufacturer. In this regard, the PCB prototype is vital in the possible deployment of the tags in a small-scale trial.

    References:

    1
    Lukas Dudkowski, IR Location Tracking System, Columbia University, NY, Spring 2002.
    2
    Lukas Dudkowski, Ubiquitous Computing with IR/RF Tags, Columbia University, NY, Summer/Fall 2003.
    3
    Parallax Corp. Basic Stamp User Manual, v2, Parallax Corporation, www.parallax.com
    4
    Jiro Dokeh, Basic Stamp Circuit Diagrams, Personal Site.