Seven Segment Displays (but in avionics)

[Brent Hilpert]

Allison wrote:

> FYI: those things are considered rare as hens teeth as most systems
> that use them have burnt them out. One series of ARC (used in cessna
> aircraft) radios had them as they were bright enough for day use
> and I hear they cost about 100$+ per digit to replace.
> Allison

  Do you have any more specific model information regarding these aircraft radios (what is the ARC series?):

  Some time ago I noticed a small, somewhat-odd module of folded-up ~2 in. by ~6 in. printed circuit boards with a row of 10 7-segment incandescent displays in the trash [*]. I pulled it out, out of curiosity. It really was trashed: no case, no identification, mangled PCB interconnect wires, most of whatever it belonged in was gone. Turned out it contained a 4004 processor and other MCS-4 support chips. Some reverse engineering, application of appropriate supply voltages, assorted repairs (including constructing a substitute for the faulty MCS-4 4201 clock generator IC) and it was a functioning embedded 4004 system, albeit quite useless as anything but a curio/artifact. By appearance and function it is the digital control/display/front-end portion of a PLL-synthesised-tuning avionics radio, perhaps a NAV/COM unit (standard dual side-by-side tuners, right side tunes 108-118 MHz, left side 118-135 MHz (from the displays)). IC date codes are circa 1977. All the analog/RF stuff is missing. (I have since mounted it with a power supply to make it into a '4004 display'. One can turn the knobs and push the buttons to change the frequency display. The 4004 does all the processing between the knob inputs and 7-seg-display outputs, as well as feeding the divide-by-N factor to the missing PLL).

  But I have wondered just what the make/model of the full unit is. Another distinguishing characteristic is that it on both the far right and left sides there is a column of 3 square (~3/16") white pushbuttons for preset frequencies. Does any of this description match the avionics units you have in mind?

[ * In the trash at the mentioned-in-earlier-messages radio museum.  Barbarians. ]