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Burroughs C3146 Electronic Calculator
Updated 8/31/2012

The Burroughs C3146 is an early implementation of a portable (but definitely not hand-held), use anywhere electronic calculator. The machine uses a flexible power supply which can operate off AC power, internal Nickel Cadmium rechargeable batteries, or via a special plug on the back, a 12V automobile power plug. The guts of the C3146 are actually made by Sharp for Burroughs, as is common among early Burroughs electronic calculators. Burroughs had a long-standing relationship with Sharp whereby Sharp would provide the electronics for Burroughs, and Burroughs would put the guts into their own cabinets, and provide all of the marketing, sales and service for the machines. This C3146 was built in the late 1970 timeframe, based on date codes on the LSI IC's in the machine. The C3146, and its Sharp counterpart, the QT-8B, were follow-ons to the groundbreaking Sharp QT-8D, and were predecessors to the first battery-powered portable electronic calculators, the Sharp EL-8 and its Facit-badged clone, the Facit 1111.

The 9-segment Itron Vacuum Flourescent Display Tubes

The Burroughs C3146 is a simple four-function, 8 digit floating decimal calculator. It uses individual tube-type vacuum fluorescent displays called Itron tubes. Itron tubes use a unique segmented arrangement to form digits which look more swoopy than the more traditional seven-segment displays which are so common today. Itron tube-type displays are most characteristically identified by the way they display the digit '0', which looks more like a 'c' flopped on its back. The Itron tubes in the C3146 are made by the Japanese component manufacturer Iseden, and have part number DG10B for the number tubes, and SP10 for the sign/battery condition indicator tube. The Itron tubes used in the C3146 are slightly different than those used in the Facit 1111 in that the tubes in the Facit machine only have eight segments versus the nine segments in the tubes on the C3146. On the C3146, the right-most Itron tube is a special tube used for indicating if the number on the display is negative, and also if the charge on the internal NiCad batteries is running low.

The LSI IC-based Brains of the Burroughs C3146

The brain of the machine is made up of a 4-chip Rockwell-made (but Sharp-designed) LSI chipset. The LSI's have part numbers 2251, 2256, 2266, and 2271. Two other IC devices provide support for the calculator chipset; a can-packaged device which is the clock generator for the chipset, with a DIP-packaged Hitachi HD3103(Quintuple P-Channel MOSFET Transistors) providing support circuitry. These IC devices are all mounted on a printed circuit board that plugs into an edge connector connecting the brains to the rest of the machine. The "CPU" of the machine is virtually identical in design to that used in the slightly later and more compact Facit 1111 and Sharp EL-8. The display tubes and associated driver circuitry reside on a separate board that plugs into another connector, which is connected to the keyboard module and the calculating board via hand-wired connections. The machine uses a rechargeable NiCd (Nickel Cadmium) 7.5V internal battery pack, made of six 1.25V cells. The power supply extends along the back section of the machine, with two sockets on the back panel of the machine, one for connecting 120V mains power, and the other for plugging in the "Car Adapter" to run the calculator from 12VDC automobile power. The optional Car Adapter sold for $11.

Internal View of the Burroughs C3146

The keyboard of the machine is a joy to use, with a very high quality feel to it. As is so common on calculators of this era, magnetic reed switches are used for reliability and their 'clean' (very little contact bounce) connections. The machine is pretty straightforward to use, with the only complication being a dual function multiply/divide key. To multiply, the first number is typed in, followed by the [X÷] key, then the second number is entered, followed by the [+=] key to calculate the product. The same sequence is used for division, but rather than pressing the [+=] key to get the result, the [-=] key is pressed to perform the division. The [-=] key is unique, as the the "=" has a dot above and below it, to help signify that this is the key to be used to get the answer for division problems. Similar Sharp-made calculators did not have this nomenclature. The keyboard panel also has a three-position slide switch that serves as the power switch, and selects the type of power the machine is to run on, with positions for "OFF", "BATT" (for battery or car adapter power), and "ON" for use on AC power.

The C3146 is fast, with all calculations providing results virtually instantly. The machine indicates overflow (or divide by zero error) by clearing the display to all zeroes, and lighting all the decimal points. The error condition is cleared by pressing the [C] key. The machine actually calculates all results to sixteen digits, but has no provision to display the least significant eight digits of any result which exceeds the eight-digit capacity of the display. In cases where the result is larger than 8 digits, the decimal point disappears from the display, but its position is kept track of internally. For example, one could perform the following calculation:

12345679 X 18

which would result in "22222222" (with the least significant '2' not being displayed) showing on the display with no decimal point visible. Dividing this answer by 10 would result in "22222222.", which, within the limits of the eight digit display, is correct.

Text and images Copyright 1997-2012, Rick Bensene.