Russ Hoffman's OS-9 based wearable computer

Concept

Some secondary goals include low cost and ready availability of parts. I'd like to be able to construct the entire wearable with no "exotic" components, so that virtually anyone can reproduce the work without having difficulty in finding or affording the necessary components.

The choice of OS-9 as it's operating system is for the following reasons:

• OS-9 is small. The complete kernal, device drivers, device descriptors, and file managers total less than 64 kilobytes.
• OS-9 applications are small. The entire OS, including all standard utilities, requires less than 1.5 MB of disk space.
• OS-9, and all of the applications running under it, is completely ROMable. This calls for fewer disk accesses, and lower power consumption.
• OS-9 is very memory efficient. Programs are re-entrant, and most utility programs are coded in assembler, making them small. Lower memory requirements translate into lower power requirements and lower hardware costs.
• OS-9 is real-time and multitasking. This allows easy development of daemon processes and background tasks (such as a Remembrance Agent, calendar reminder, etc.)
• OS-9 is multiuser, which allows user authentication with no extra effort. It also affords the owner to loan his wearable to another user, who has a separate account on the machine.

The system consists of two or three subsystems: The wearable CPU, the wearable ASCII terminal, and the optional RF modem. My primary use for the machine is the office/college campus environment. The system will be primarily used for note-taking and code development. (GCC is available for OS-9).

I have some interesting ideas on ways to connect the wearable to the outside world.

Hardware Description

• I. CPU unit
  • A. 10 x 15 cm cards, based on 68k bus
    • 1. CPU card (Click here for PCB layouts)
      • a. 16.67 MHz 68306 (68EC000 core + 2 serial +DRAM controller + timer + bus logic)
      • b. 512K EPROM (could put all of OS-9 in ROM for fewer disk accesses -- less power!)
      • c. 2 RS-232 serial ports
      • d. Stackable (cards are parallel to each other) Expansion bus
      • e. Will run OS9 v2.4
    • 2. DRAM card - 2 to 16 MB DRAM (uses SIPs)
    • 3. I/O card
      • a. Parallel I/O
      • b. WD SCSI controller
      • c. Floppy controller (I believe)
    • 4. About 3 watts for this stack
  • B. Hard disk - 125 MB Quantum Go Drive
    • 1. 2.5" x 0.5" thick form factor
    • 2. 2.5 watts
    • 3. Quick start/stop times (can power down spindle motor to save energy, but spins up & down quickly so as not to be annoying to do so.)
  • C. Case & batteries. Should be 12cm x 17cm x 6cm
  • D. Hardware is low power by design, from the ground up.
• II. Wearable ASCII terminal
  • A. Chording keyboard
    • 1. Homebrewed, constructed similar to Twiddler, except uses three rows of four conductive rubber tactile keys (similar to those on HP 'scopes), plus thumb modifiers (CTRL, SHIFT, MACRO)
    • 2. Mounted to arm-mounted clamp, with ratcheting pivot mechanism that allows keypad to be folded back flat against back side of forearm when not in use.
  • B. 68HC11 (or similar) microcontroller.
    • 1. Scans keypad and debounces. Translates chords into ASCII codes or macro sequences.
    • 2. Battery backed-up CMOS SRAM stores config info and macro set. Escape sequences used to download macros from host computer.
    • 3. Receives incoming serial data and writes character data into video ram. Performs terminal emulation of some yet undetermined terminal type, likely custom, supporting at least cursor movement, normal/inverse video, and line/character insert/delete (to be able to run Emacs)
  • C. Video driver.
    • 1. Displays character data from video RAM that HC11 draws.
    • 2. Supports bitmapped graphics, for downloadable fonts, and crude graphics-terminal capability.
    • 3. Allows multiple width fonts for dealing with varying display quality (depending on type of viewfinder)
    • 4. Outputs composite video (to interface to camcorder viewfinder.)
  • D. Head-Mounted Display
    • Camcorder viewfinder
      • Inexpensive
      • Somewhat readily available
      • Can develop on larger composite monitor first; need not use HMD to develop on.
    • Accepts NTSC monochrome compositve video
    • Up to 80 columns
  • E. RS-232 serial port
    • 1. Standard interface to many computer systems, makes the wearable ASCII terminal portable across CPU platforms.
    • 2. Allows the ASCII terminal to be used with standard modem equipment independant of a host (wearable) computer.
• III. Wearable RF/cellular modem (optional)
  • A. Could be simple RF
    • 1. Ups:
      • a. Low cost
        • i. cheap parts
        • ii. no subscriber service
      • b. No license required (unless amateur band)
      • c. Simple design - use 49MHz or 75 MHz radio control freq stuff. (off the shelf)
    • 2. Downs:
      • a. limited range
      • b. susceptible to interference
      • c. can generate interference (crashes R/C airplanes, etc.)
      • d. Secure data must be encrypted
        • 1. Not allowed to encrypt on Ham bands
        • 2. Requires CPU for encryption (see C below)
  • B. Could be cellular
    • 1. Ups:
      • a. Reliable service, with greater coverage
      • b. Can use existing telephone modem technology
      • c. Encryption is legal (not a Ham band!)
      • d. Some cell phones scramble automatically anyway
      • e. User might already own a cell phone
    • 2. Downs:
      • a. Subscriber fee
      • b. Requires a cell phone (bulky/awkward)
  • C. Interfaces directly to EITHER wearable CPU's serial port OR wearable ASCII terminal's serial port.
    • 1. More flexible design
    • 2. Allows less power consumption when not using local (wearable) CPU resources.

The wearable ASCII terminal plugs into the console serial port on the wearable 68306 CPU. This allows the display device and the 68306 CPU unit to be developed separately.

Return to Wearables main page Last modified Wed Nov 22 12:45:01 EST 1995