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Crown CL-80K Electronic Desktop Calculator

The Crown CL-80K is yet another example of the fact that just about everyone in the electronics industry got into the calculator business before the market shakeout in the late part of the early 1970's. Crown Radio Corporation in Japan was known for transistor radios, the previous boom market before electronic calculators came along. By the 1970's, the market for transistor radios had become pretty saturated, and so, many radio makers looked for alternative markets to sell into, and electronic calculators seemed a good choice for many of them.

Inside the Crown CL-80K

This machine was built in the middle part of 1972, at a time when the impact of large-scale integrated circuit "Calculator on a Chip" implementations were starting to make it relatively easy for just about any electronics manufacturer to build a calculator. Building a calculator was no longer rocket science like it was in the days of machines like the Monroe 740 or even later, more complex machines like the Wang 720C. All that was needed to build a basic calculator was a "calculator on a chip" IC, a sprinkling of transistors or small-scale IC devices for display drivers, a relatively simple power supply, a keyboard, and some form of display device. All of the rocket science had been distilled down to the insides of the Large Scale integrated circuit. At the time, Texas Instruments was flooding the market with a whole series of TMS010x single-chip calculator IC's, creating lots of opportunities for anyone that had electronics manufacturing facilities to get into the calculator business.

The Brains of the CL-80K

The Crown CL-80K is a basic four-function AC-powered desktop calculator. It is based on Texas Instruments' TMS0105 calculator IC. It has eight digits of capacity, and utilizes full floating decimal. The machine uses a vacuum-fluorescent display consisting of nine individual VF tubes. The left-most tube is coated with a red film, causing inidications in this tube to show up red on the display. This special tube is used for indicating the sign and error/overflow condition of the calculator. The rest of the tubes have no such coating, and show numbers in the normal blue/green tint that vacuum-fluorescent tubes provide. Each tube uses a standard seven-segment rendition, with a right-hand decimal point. The displays are driven by discrete transistor (2SA675) drivers. The calculator uses a conventional linear power-supply, with transistor regulation for the voltages the supply delivers. A somewhat uncommon feature of the machine is that the calculator can run on 220V or 117V, settable by a switch which is accessable from the bottom of the calculator.

Detail of Main Board (Note TMS0105 Calculator on a Chip)

The CL-80K operates as usual for such a machine. The machine uses the standard "+=" and "-=" keys for addition and subtraction, with the "+=" key used to calculate the results for multiplication and division. The "=-" key also provides termination for multiplication and division, but negates the result. A "CI" key clears the display for correction of incorrectly inputted numbers, and the "C" key clears the entire machine. A constant function for multiplication or division is activated by a slide switch on the keyboard panel. When the switch is in the "K" position, the calculator keeps a constant multiplier or divisor 'locked in' for repeated calculations. The display features leading zero suppression, and numbers are right-justified in the display. The machine provide full floating decimal point, with the decimal point automatically positioned for maximum accuracy of the result.

Closer View of CL-80K Display (Note Red "-" Indication)

The Crown CL-80K indicates the sign and overflow status of the machine on the left-most, red-tinted display tube. A "-" lights to indicate a negative result. If the user overflows the machine by entering too many digits, this tube will display a "C", and further digit input is ignored. The "C" indication will persist through calculations until cleared by pressing the "C" or "CI" keys. An arithmetic overflow will result in a "u" being displayed on the status tube, and the keyboard locking, preventing futher operation of the machine until the "C" key is pressed to clear the machine. Division by zero also triggers the "u" overflow condition. The calculator is not a speed-demon, with addition/ subtraction taking perhaps 0.1 second, and multiplication and division operations taking up to 1/2 second to perform, with 'all-nines' divided by one taking at least this amount of time. During calculation, the displays are left active, and flicker about as the calculation proceeds.


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