At a Glance

In 1991 and subsequently, I provided the following design elements for this Heads Up Technologies aviation-industry series of products:

• Complete hardware design:  schematics and circuit-board layouts for 9 circuit-boards.
• Complete firmware design:   this is a 3-processor design, with each processor executing different firmware.  This involves a large but unknown quantity of C-language and Intel-8051 assembly-language code.
• Documentation:  100 pages for specification and certification purposes, plus unknown quantities for internal engineering purposes.

Background

This is an "annunciator panel" installed in all Cessna CitationJet-series aircraft.  An "annunciator panel", at the simplest level, is simply a box with electrical inputs on the back and lights on the front.  When an electrical signal becomes active, the associated light turns on.  Thus, the pilots can be warned of dangerous conditions like generator failures or flaps not set properly.  Of course, the IAWS unit goes far beyond this simplistic model, in some of the following ways:

• Audio annunciations are provided in addition to visual annunciations.  For example, in case of a battery over-temperature condition, the red "BATT O'TEMP" light is lit and the pilot hears "BATTERY OVERTEMP!".  Actually, many of the audio annunciations are somewhat more complex, repeating a certain number of times with certain delays in between, and/or being preceded by alert-tones.
• The behaviors of the visual annunciators are actually much more complex than described.  For example, most lights begin flashing when first activated, then become lit steadily when an external reset button is pressed, and then finally become dark when their activating signals are removed.  Many of the lights are much more complex than this, with built-in delays upon being activated or deactivated, being activated or deactivated only upon certain combinations of signals, etc.
• Because of the important functionality provided by the unit, a certain level of redundancy is provided by separating the audio and video annunciations into two separate CPUs.
• The visual annunciations aren't really light bulbs, but are actually complex sandwiches of custom LCDs with LEDs to provide reliability with both day and night visibility.
• The electrical signals used to activate the annunciations aren't simple identical on/off signals.  Each differs from the next, with programmable polarity and voltage ceilings/floors.  Some signals are actually active only when pulsing.


This product has proved very important to Heads Up, and at this writing (about 10 years after the initial product introduction) is sold in roughly the same quantities as when first introduced.  Many variations of the product have been requested by Cessna, and continue to be introduced approximately every 6 months.

The initial development of the IAWS was also signficant in terms of its "firsts" and its consequences:
 

• In spite of the complexity of the product (9 circuit boards, 3-CPU design with 3 separate sets of firmware), I was forced to design the product on a very ambitious schedule, with no break between it and the design cycle for the preceding product.  The prototyping phase took about 4 months.
• Documentation requirements for Cessna necessitated the invention of the Heads Up "drawing package" system, an internal engineering system that had not previously existed in any satisfactory sense, but took the manufacturing and engineering documentation of our products to a much higher level that had previously existed.  I contributed heavily to this system, and all subsequent replacement drawing-package systems were essentially my personal inventions.
• This was by far the most complex design that I (or Heads Up) had created at that time.
• I carefully crafted the firmware and hardware to be very reconfigurable, and to interact heavily with PC-based diagnostic software.  Because Cessna's requirements for the product were quite variable at the beginning, these characteristics came to our aid on several occasions to drastically reduce re-design time, and to give Cessna the impression that Heads Up's engineering was extraordinarily responsive.  This has contributed to the highly favorable position (in terms of new business) which Heads Up has since enjoyed with Cessna.