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Calculators: Desktop: Sharp Compet CS-2109

(c) Emil Dudek 2011

Size (approx):

215mm x 240mm x 30-55mm (keyboard), 115mm display  (w,h,d)
Weight 992g excluding cable


Mains (240V 50Hz, 2.3W) power only through a permanently fixed mains cable of considerable length.
Display: 12 digit green VFD with additional symbol clusters at each end for memory (M), error (E) and negative (-).  The latter is on the far right below the memory sign.  There are unused symbols on the left cluster (another negative sign and a left pointing arrow), and on the right cluster (a I and II for double memory indication).  The display has upper commas for thousand notation.
Features: Standard four functions with percentages, square root, count total, four function memory, register exchange, delete, double zero entry and mark-up. Switches for constant, round/round up/round down. floating /fixed /accounting format, auto-accumulator. Semi-RPM Logic.
Age: 1977
Manufacturer: Sharp Corporation, Made in Japan, serial No. 75008396.


A sturdy workman like calculator which is a bit a design jumble.  Solid logic except for the input overflow  and the divide to negative zero bug but useful range of functions.  Very easy to read tilted display. Same case as the less advanced CS-1109. There was also a CD-2109A version.

Case and Design: The two-piece case is made from smooth cream plastic whilst the top section is a mixture of matt and smooth black plastic.  There is a very pronounced raised section at the back which tilts the green filtered display at 45 degrees.  To the right of the display is a black and yellow printed metallic label that sits in its own recess.  There is also another small metallic label printed "Made in Japan" to the far left below the display.

Keys and Switches: The top most switch is for on/off. The next row consists of a constant switch (K), rounding options (up, 5/4, down), decimal point switch (F63210A), a memory summation switch and two white keys for change sign and (MU).  The remaining keys are grouped in four banks; cancel keys, numeric keys (including 00), basic function keys and finally a group of "other functions" and memory control.  The whole thing is a bit of a mess really.
Construction: Remove the two screws from the bottom and the third from the top and the whole black front section will come off with a gentle pressure to pop the top and bottom lugs.

Boards: There is just one board that holds the key assemblies, switches and display unit.  It sits loosely inside, not a screw in sight.  Oddly enough the components are mounted on the underside.  I imagine that this makes connection to the keys easier.  The board is shaped to accommodate the mains transformer (top right) which is screwed down.
Components: 1 x cpu: Hitachi HD38401 7F 35, 36 pin DIL, 0.6" width
1 x 12 digit green VFD display: flat tube with left and right symbol clusters
1 x transistor
17 x diodes
8 x capacitors
2 x resistors
1 x mains transformer: P1417CC 957Z T
1 x board transformer: 1414 TDK Japan
2 x fuses in holders

Minimum components - and most of them are for the power supply regulation and VFD voltage.  The IC is driving the display direct.
(image right is the underside of the board)

Logic comments: (CE) is used once to cancel the last number entered and (C) to clear the whole calculator
(CT) displays the count total, the number of numbers you have entered - useful for finding averages.
(->) deletes the last number entered but can also be used as a error recovery key
(00) allows more rapid number entry, especially in automatic decimal mode (A on the points switch)
Input overflow is not suppressed, keying a thirteenth digit results in an overflow that is recoverable using (->)
Constant function is switched in with the "K" switch and operates on multiply and divide only
The rounding switch can select round up (^), round up/down (5/4) and round down (v)
The decimal point switch can be selected between floating "F", fixed "6,3,2,1,0" and automatic financial mode "A" for $x.xx entry
Negative numbers are shown with a minus in the far right symbol cluster allowing full twelve digit negative numbers
A summation switch "S" (sigma) adds the result of every calculation the memory
Divide by zero shows a "0." and "E" in the far right symbol cluster and is not recoverable
Overflow shows the result and "E" in the far right symbol cluster and is recoverable using (CE) or (->)
Memory storage is indicated by "M" in the far right symbol cluster
Overflow in memory flags an error (with "0.") and is not recoverable, but retains the original number
The change sign key (+<>-) can be used in mid number entry
The register exchange key (^v) will also exchange the answer for the first number entered
Square roots of negative numbers are not allowed; it displays the result and error indicator and is recoverable using (CE) or (->)
The (MU) key does is for Mark-Up and is used to increment or decrement a value by its percentage.
It suffers the divide to negative zero (once) bug: key in (1)(+=)(2)(-=) to give "-1." now divide repeatedly by ten until you get "-0.", one more division will give you zero showing you the extra level of precision in the complimentary algorithm