Facit Model 1135J, S/N 3500315
Functions: ASMD, K, square root, 3 memories
Technology: MOS-LSI (Rockwell, 7 chips)
Display: 16 digit, Nixie tubes
Dimensions: 300W x 330D x 105H, weight 4.24kg
Manufactured: Sharp, Japan, 1971
Facit Model 1135J, S/N 3500315
Functions: ASMD, K, square root, 3 memories
Technology: MOS-LSI (Rockwell, 7 chips)
Display: 16 digit, Nixie tubes
Dimensions: 300W x 330D x 105H, weight 4.24kg
Manufactured: Sharp, Japan, 1971
The Facit organisation built an extensive range of mechanical calculators at Atvidaberg in Sweden from the early 1920s to the 1970s. In 1966 they introduced the first of a range of electronic calculators manufactured by Sharp in Japan. The design and function of the Facit-branded machines is generally similar to the Sharp "Compet" machines of the time.
The Facit Model 1135J from 1971 is a (relatively) compact desktop machine with a 16-digit display and three accessible memories. It is based on a set of seven MOS-LSI chips from Rockwell in America.
This page gives a brief overview of its construction and operation.
Internal view
The main circuit board, display board, and power supply are mounted in three metal carriers in the lower section of the case. The main board is at the bottom, with the display and power supply above. There is a metal shield plate attached to the base, but it is not electrically connected.
Main board
The processor circuitry is contained on one double-sided phenolic board measuring 255 x 185mm. The board is mounted in a metal frame, which attaches to the base of the machine with two screws. There are two 2x22-way edge connectors near the centre for the keyboard (left) and the display board (right). The 2x11-way connector at the rear is accessible externally behind an un-marked cover panel at the rear of the case.
The processor uses a set of seven Rockwell MOS-LSI chips in 42-pin ceramic flat-packs. The part numbers are 10061 to 10066, and 10328. The date codes range from March to October of 1971. There are another 8 NEC chips in DIL packages, and about 100 discrete components. The circuitry operates from a single regulated -25V DC supply which is connected via the display board.
The main board has SHARP etched into the copper pattern in the upper right, but is also stamped with a date code "46.8.26" (26 August 1971) in the format used only by Canon. (The years are counted from Canon's formation in 1925). Canon date codes are often found in machines from other calculator companies, including Sharp and Casio.
Display board
The display board measures 255 x 100mm, and carries a Canon date code 46.8.16. It is supported in a metal frame which mounts above the forward section of the processor board, and is secured by the same two screws.
The numerical display uses sixteen multiplexed Nixie tubes with discrete-transistor drivers. The tubes are 12mm diameter mounted on 14mm centres, with numerals 12mm high. The tubes have a comma symbol at the lower left (which is used as a thousands separator), and a decimal point at the lower right.
A special tube at the right-hand side has indicators for the three memories, a minus sign, and a large E for error. The flying lead at the right is the incoming connection from the power supply.
Power supply
The power supply is a self-contained module which mounts above the main board at the rear of the case. It has an IEC input socket and a small mains filter board, with provision for a mains voltage selector (not fitted to this model). The input rating is 240V AC, 16W.
The power supply produces a regulated -25V DC supply for the logic circuits, and +190V DC for the Nixie display tubes. It has a plug and socket connection to the display board via the three pins at the upper left.
Keyboard assembly
The keyboard assembly is mounted in the upper section of the case, and is attached to the processor board via a card edge connector on a flying lead.
The assembly consists of four separate sections, which are mounted on a substantial metal plate. The keyboard uses glass reed switches, operated by moving magnets on the ends of the keystems. The main numeric keypad has a mechanical interlock to prevent more than one key being pressed at a time. There is an inaccessible 24-pin DIL IC, presumably some form of encoder, mounted on the under side of the left-hand circuit board.
The control panel of the 1135 is dominated by the three sets of memory control keys on the right-hand side. Indicators at the right of the display show when the memories are active.
On the left of the keyboard are two pairs of slider switches which set the decimal places (0 to 7 or floating) and roundoff for the display and the memories separately. There is a latching K (for constant) key, and RV to swap the display register and the internal buffer. Clear and Clear Entry operate as expected.
The four function keys in the centre operate as expected, with Plus and Minus working in adding-machine fashion. The Multiply and Divide keys have lamps behind the symbols to show when an operation is pending (including when K is active).
Although it is not obvious from the keyboard, the machine provides both square and square root functions by using the Mult and Div keys without a second argument. For example, 2 Mult Equals produces the square (4), while 2 Div Equals produces the square root (1.414).
The display is right-aligned according to the setting of the decimals switch, with leading zeros suppressed. Trailing zeros are preserved in floating mode - 2.0 x 2.0 produces 4.00, not just 4. The comma symbols provide active thousands separators in the area to the left of the decimal point.