+Home     Museum     Wanted     Specs     Previous     Next  

Passport CA-850 Desktop Calculator

This calculator is an example out how popular it was in the early '70's to get into the calculator business. Many companies sprouted up in this timeframe to satisfy a very demanding market. And, many of these companies died off almost as fast as they came along in the big shakeout of the calculator market in the late '70's and early '80's, as inexpensive battery-powered, handheld calculators mostly evaporated the market for AC-only desktop calculators. This machine, a clone of the much more well-known APF Mark I, was made in Japan in the early 1973 timeframe. With the advent of simple single-chip LSI calculator designs, and at that time, still relatively inexpensive labor costs in Japan, the "generic" calculator became a reality. Japanese manufacturers would build cheap desktop machines, with an open space on the top of the cabinet for a name plate, and a space on the back panel for a model/serial number tag, and sell them like hotcakes to the various entrepreneurs around the world who thought that getting into the calculator biz was a quick way to get rich. The only thing that the retailer would have to do is stick a nameplate and serial number tag on the machine, establish an appropriately greedy sales price, and find outlets to sell the machines to an eager marketplace.

Internal view of Passport CA-850

The Passport CA-850 is a very basic 8-digit four function desktop calculator. It runs on AC power only, and uses neon gas-discharge tubes for display. The machine operates in floating decimal, or can be set to fixed decimal point locations of 2, 3, 4, or 5 digits behind the decimal point via a slide switch on the keyboard panel. Another slide switch turns the constant function on or off.

A closer view of Gas-Discharge Display and Driver Circuits

Internally, the CA-850 is very simple. It is based on the Texas Instruments TMS0101 single-chip calculator LSI. The 9-tube gas-discharge tube display is driven by discrete transistor drivers. Gas-discharge tubes work on the same principle as Nixie tubes but rather than have electrodes in the shape of the digits, the electrodes are grouped into the now-familiar 'seven-segment' arrangement. This arrangement required fewer interconnections, was easier to multiplex, and the tubes were less expensive to manufacture than Nixie tubes. The display tubes are grouped together and held in place by a plastic frame.

Detail of Gas-Discharge Display Tubes in Operation (note 'C' Overflow Indication)

The display tubes are wired to a small auxiliary circuit board that has hand-wired connections to the main board. The left-most display tube, while a standard seven-segment display tube, is used for indicating error/overflow, and negative sign indication. An overflow results in a 'C' being displayed, with a negative overflow showing up as 'E'. Division by zero also results in an overflow indication. The overflow condition shows the most significant eight digits of the result, but the only way to unlock the machine after an overflow is to press the "C" key to clear the calculator. The "CE" key allows erroneous numeric entries to be cleared from the display. The remainder of components in the machine are all discrete, with a clock generator, power supply regulation, and display driver components completing the circuitry. The keyboard assembly is wired to an edge-connector that plugs into the main board of the machine. The keyboard appears to use key modules that contain a magnetic reed-switch as the switching element.

Profile view of the Passport CA-850

The Passport CA-850 is relatively fast, with the 'all nines' divided by one benchmark taking about 1/10 of a second. During calculation, the tubes are not blanked, but calculations occur quickly enough that all that is really perceived is a slight 'flicker' of the digits as the result is generated.


Text and images Copyright ©1997-2011, Rick Bensene.