4004 Microprocessor

This is a monument to the Intel 4004 microprocessor and MCS-4 family of integrated circuits. The module of bare printed circuit boards and 7-segment displays mounted on top of the base are the digital control portion of the PLL-synthesised-tuning system from some avionics equipment. The digital control is based around a 4004 CPU and other MCS-4 ICs. Date codes on the ICs are from mid-1977.

The module was retrieved from a trash bin after being noticed by a chance observation. I pulled it out out of curiousity and noticed the 4004. It was in poor condition at that point with many of the board interconnections broken and some other damage. The remainder of the piece of equipment it came out of was nowhere to be found.

The module was reverse-engineered, repaired and powered-up. Various problems were encountered in the repairs. Several of the photo-transistors in the quadrature optical-interruptor tuning controls were bad - the unit dates from before standard or common optical interruptors were produced and the photo transistors were difficult to replace. The 4201 clock generator chip for the 4004 was bad and I had to rob one from another piece of equipment and then build a substitute to keep that equipment working.

The size, build-quality and dual side-by-side controls and display suggested the module might be part of an avionics NAV/COM unit. Once it was powered-up it became clear this was correct: the displays presented numbers in the aviation NAV/COM band. The right side tunes 108.00 - 117.95 MHz, the left side tunes 118.00 - 135.97 MHz. A hint from an aviator and some searching eventually produced a match with the front panel of an ARC (Cessna) RT-485A NAV/COM radio.

Essentially useless otherwise, the decision was made to turn it into a display of an embedded 4004 system from the 1970's.

The base was constructed from some scrap aluminum, plexiglass, brass, stainless-steel hardware and mahogany-veneer plywood. It contains a power supply for the 4004 module.

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Top view of monument, the boards of the module are hinged and are folded open for the display.

A closer view of the 4004 family chips. The 4 gold-capped chips are 4001 mask-ROM chips containing the firmware. To the right of those is a 4002 RAM chip and the 4201 clock generator (socketed). The 4004 CPU is to the left of the ROMs. (The remaining chip on the far left is a CMOS shift register used for long term storage of user state).

Opened up for access to the power supply.

Closer view of the power supply.

4004 Monument
2009 Mar