Prinztronic C15

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Calculators: Handheld: Prinztronic C15


		Size (approx):	80mm x 172mm x 21mm (max) (w,h,d) Weight 140g excluding batteries.
		Power:	6V DC, 4 x AA size battery. Also accepts adaptor (6.5V DC, 23MA [sic] 2.6mm by 11.5mm jack size, centre negative) through a socket on right hand side in line with the top of the display. The battery cover has a label inside showing the orientation of the batteries - which is essential as it is otherwise difficult to tell how to put them in.
		Case:	Tall thin case made from two pieces of dark blue matt plastic. The upper area (where the batteries sit) has a ridged design with an inset area for an embossed, silver printed black label. The red plastic display filter is tilted and has a horizontal convex section for additional magnification. Below this is a metal panel with black text for the power and decimal point switch. The inset keys are touch-membrane plastic. There is a red display shift switch on the left hand side in line with the display.
		Display:	6 digit red LED with bubble lens and an isolated extra point LED for negative indication
		Features:	Basic four function with 6 + 6 digit display and fixed zero or two digit decimal. RPN logic.
		Age:	est. 1973
		Manufacturer:	Made in Hong Kong, serial number 208889 on a label inside the battery cover.
		Comments:	Very unusual calculator that uses touch membrane panels rather than moving keys. My example does not work well with some keys not responding at all. The battery compartment is a little too small and puts undue pressure on the top edge, which being rather thin is prone to cracking. The logic is appallingly archaic with no floating decimal mode, RPN input, divide by zero bug, negative zero bug, no recovery and an overflow state which doesn't match the manual's instructions. The true 12 digits are useful though. The original case is soft, patterned black plastic with flip over top and front popper closing. It also has a top carry strap. Definitely one for your collection as an oddity at least. Looks exactly like the Hanimex-Tabulex 666.

Components:	2 x 3 digit LED units with individual bubble lens 1 x single point red LED and at least: 1 x IC 17 x diodes 14 x transistors 4 x capacitors 32 x resistors unable to examine as hidden by the keyboard assembly
Boards:	The main cpu board sits in the rear section with the keyboard assembly on top. The two are joined by 17 short, strong soldered wires so cannot be separated easily.
Construction:	Remove the two screws from the rear. Then gently prize the sides apart to pop the internal lugs, one in the middle either side. Hinge off the bottom and then to the right hand side as the adapter socket cables join the two sections together.

Logic comments:	(C) clears the calculator, there being no cancel entry function
	Input overflow is not suppressed, inputting a thirteenth digit results in an overflow which is not recoverable
	You can input and manipulate up to twelve digits by pressing the display shift key to see the 6 most significant digits
	There is automatic constant on all four functions
	It is semi Reverse Polish Notation: to do 2-4 key in (2)(+=)(4)(-=)
	Negative numbers are represented by a discrete red LED at the far left digit thereby allowing full twelve digit negative numbers
	Divide by zero blanks the display and is not recoverable
	Overflow shows "0000.0.0." even though the manual says that all six decimal points light up and you are supposed to be able to see the result. It is not recoverable.
	It suffers the negative zero bug; key in (1)(+=)(2)(-=) to give "-1" then (1)(+=) to give "-0"
	You can choose between zero and two fixed decimal places with a switch - there is no floating point mode
	The manual states (read this two or three times!): "Division: The number of figures in the divisor cannot, usually, exceed 10 and the quotient and dividend are limited to a maximum of 11 figures. In the divisor please note that the number of decimal places entered count towards the total number of figures entered in the dividend." Got it?

		Notable quotes from the manual: "Why A 'Calculator?' This solid state electronic calculator is a most sophisticated instrument designed to make life easier for the accountant, business man, engineer, shopkeeper, bookkeeper, house-wife, student... virtually everyone and anyone who handles figures." "...more sophisticated than an adding machine... This calculator is far more versatile: with 12 digit capacity it can add, subtract, multiply, divide, perform mixed arithmetic, extract percentages... almost anything that's required in the ordinary course of business..." "Use only high quality ... AA cells since others may not have the life or stamina required to give long and trouble free service."
The double tuck end box measures 105mm by 178mm and is 43mm deep. Printed in blue and half-tone black it calls the special keys "Sensor Controls" and boasts of its twelve digit capability. A sticker on one end duplicates the serial number - which on my example is different: 208680. This is close enough to make me think it may have got mixed in the shop.	The manual measures 96mm by 150mm and has 20 pages which are black throughout, but the cover is black blue and red. Plenty of calculation examples with lots of descriptive text and marketing blurb. Printed by Public Printing Press, Tel 5-620211-2, which I presume was a Hong Kong number. Whilst the text is in English only, the monetary examples show dollars.	My example also came with a red text printed sheet "External Power Adaptor" measuring 125mm by 102mm. It warns of the correct adapter polarity and not to plug it in with the calculator on. There is also an A4 photocopied typed sheet covering Keyboard Operation, Battery Compartment, Low battery Indication (or rather the lack of) and Limitations (you must have 2 decimal point selected to enter numbers with decimal points).
The keyboard system was unusual enough that an extra A4 sheet contained additional instructions for use. They must have had some problems judging by the need for this sheet -and they never did this type of keyboard again - so reach your own conclusions. "Keyboard Operation This Touch Sensor Type Keyboard is one of the latest developments in space-age electronic technology. In the operation of this new Touch Sensor Keyboard, a modified technique of operation to that of push button type keyboards is required. We recommend a soft but firm single pressure be applied with the ball of the finger to activate each numerical or function key. Sharp objects such as finger nails, ball point pens or pencil tips should not be used to activate the keyboard as these sharp objects may cause false entries or physical damage to the keyboard."

This scan shows the front removed and put to the right hand side. Unfortunately as the keyboard assembly is hard-wired to the cpu board; I'll have to wait for a scrap example to examine this more closely.

However typical of its early era is the large number of transistors that you can see, but the keyboard appears to also need a large number of diodes to operate.

You can also see the micro-switch on the side better on this scan - for the display shift function on the left side.

There was a different (possibly earlier) version without an adapter socket. For example see serial number 206683 (with also a black card display surround that just may be missing on mine) on Nigel Tout's fabulous web site Vintage Calculators. As my example has a printed card covering the use of an adapter and no mention in the manual, I presume this was a later alteration. The use of sticky tape to hold down the extra cables does seem to be a bit of a bodge job. Perhaps they found that this model consumed batteries at a rate of knots and decided to do something about it? Also note that this other model appears to have cross markings on the keyboard membrane.