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Calculators: Handheld: Citizen 831RD Type I
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Size (approx): |
86mm(max)
x 165mm x 22mm(max)
(w,h,d) |
| Power: | 3V DC, 2 x AA size rechargeable battery pack. It accepts an adapter/charger (CTZ-831RD) through a socket on the top side on the far left. It is a 2.5mm plug with centre positive. | ||
| Case: | Made from a two-piece light grey smooth plastic body it is notable for its prominent battery pack in dark grey plastic on the top. The whole pack slides off with batteries intact and is has a near full-width label. The back has an embossed diagram of how to remove the pack. A slightly tilted green display filter gives a bright display. Within the filter there is a recess that houses a silver printed piece of black plastic with the company and model names. The keyboard surround is brushed aluminium with black printed text. The prominent keys are squishy with long travel but work well and the blue and grey colour scheme looks quite nice. Smaller keys are used for the less often used functions. | ||
| Display: | 8 digit green VFD, with a ninth digit for negative, memory and error indication. | ||
| Features: | Standard four functions with percentages, change sign, register exchange, square root, squares, reciprocal and four function memory. Additional switch for Floating/1/2/4 decimal point definition. | ||
| Age: |
1977/8 |
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| Manufacturer: | Citizen Business Machines Inc., made in Japan, Serial No. 709 56395 | ||
| Comments: | On the large side for a handheld calculator but the wedge shape makes it easy to hold. It is equally at home on the desktop as well. The dominating battery pack case is odd but helps to keep the whole thing quite slim. The logic is very sound but the lack of overflow recovery a nuisance. Quite a large component count for such a late date. There was also a version 831RD-III. |
| Components: | 1 x cpu: Texas TMS1071NL
KBSL 7744 (date code week 44 of 1977), 28 Pin DIL, 0.6" width 1 x 9 digit VFD display flat face single tube. 2 x transistor 4 x diodes 8 x capacitors 5 x resistors 2 x resistor arrays 1 x transformer DCT-45 1 x rechargeable battery pack (two permanently connected AA-size) Column 2 x 1.2V 450mAh |
| Boards: | The keyboard assembly (GK405-1 831DK) sits above the main cpu board (IH-025a) and is joined via 14 stiff wires. |
| Construction: | Remove the battery pack by gently squeezing in the front and pulling it up. The side lugs are popped by pressing the rear section in on one side. The front will eventually lift off. Very easy to cause damage so if in doubt don't bother. |
| Logic comments: | (CE) is used to cancel the last number entered and (C) to clear the whole calculator. |
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is automatic constant on all four functions |
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| Input overflow is suppressed, inputting a ninth digit is ignored | |
| Negative numbers are shown with a "-" in the immediate left digit travelling into the far left (ninth) digit thereby allowing full eight-digit negative numbers | |
| Divide by zero shows "o” in the upper section of the far left (ninth) digit and is not recoverable | |
| Overflow shows the result with "o" in the left most (ninth) digit and is not recoverable | |
| The change sign can be used in mid-number entry but is not needed in a lot of calculations as you can use the minus key before multiply and divide. | |
| Memory store is indicated by an “r” in the upper section of the far left (ninth) digit | |
| Negative square roots are not allowed but show the result which is unrecoverable | |
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