Binatone Mastermind 02/4503

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Calculators: Handheld: Binatone Mastermind 02/4503

		Size (approx):	68mm x 127mm x 17-22mm (w,h,d) Weight 76g excluding batteries
		Power:	9V DC, 1 x PP3 size battery. Accepts an adapter (undefined but 2mm plug, centre positive) through socket on the top side at the far right. A notice on the back states "Battery must be removed when using AC adapter".
		Case:	Compact and cheap feeling design. Body made of two-piece black smooth plastic with two large brushed aluminium panels above the display and as a keyboard surround. The latter is printed black for the key labels. The upper section is much thicker to accommodate the battery and tilts the display by about 20 degrees. The red (wrap around) plastic display filter has a raised and silver printed logo. The model number is on a sticker on the back. Keys are short travel clicking type that work very well.
		Display:	8 digit red LED with bubble lens with a ninth digit for negative and memory indication
		Features:	Standard four functions with percentages and four function memory
		Age:	1977
		Manufacturer:	Made in Singapore, serial number 331312.
		Comments:	Ah! the age of cheap mass produced LED calculators at a time when everyone was jumping on the bandwagon. It was not supplied with a cover - just a small plastic bag. The logic is not too bad except for the pseudo fixed decimal bug and strange memory overflow mode. Similar models can be seen on Same Calculator. And compare the insides of these fascinating calculators.

Components:	1 x cpu: Texas ZA0571 KFSP 7650 (date code week 50 of 1976) 28 pin DIL, 0.6" width black plastic 1 x 9 digit bubble lens LED; TIL 395-9 Korea 7621 (week 21 of 1976) 0 x transistors 1 x diode 0 x capacitors 0 x resistor arrays 4 x resistors
Boards:	The single cpu board (Ref K095 A/W145247 Rev A ETCO Pat Pending No. 19916/75) sits above the keyboard assembly and is held in place by four melted plastic posts.
Construction:	Difficult this one - be careful! Gently prize the back of with a blunt (wooden) instrument whilst squeezing the front in. It helps if you loosen the power socket fixing ring. The back will pop off.

Logic comments:	(CE) is used to cancel the last number entered whilst (C) clears calculator
	Input overflow is suppressed, keying a ninth digit is ignored
	Negative numbers are shown with a "-" in the immediate left hand digit, travelling into the ninth to allow full eight digit negative numbers.
	There is automatic constant on all four functions
	Overflow displays the result flashing and is recoverable using (CE)
	Divide by zero shows a flashing "0." and is recoverable using (CE)
	Memory store is indicated by an upper "r" in the fare left (ninth) digit
	Overflow in memory is flagged and the result (shifted) is held in memory (also flashing) which is recoverable using (CE). However, if you do not recall the memory and use (C) you will clear it.
	It suffers from the pseudo fixed decimal bug: key in (1)(+)(0)(.)(0)(0)(0)(=) to give “1.000” which stays a s a fixed three decimal point number until more digits are needed or divide or multiply is used.


The box to the left is printed black and orange with the minimum of information on it. It is just about big enough to take the calculator at 70mm x130mm x 25mm (w x h x d). It is a tuck end type. A J.P Product, made in Singapore.	The very basic, four page, black only manual is also the minimum you could get away with. At 66mm x 99mm it is about as cheap and thin as you could make. It is a generic manual with the model details overprinted on the front page.	The scan above shows the calculator with the rear of the case removed. Only a few extra components: some resistors and a diode across the power supply to stop you plugging in the wrong polarity adapter. The board is attached to the front by melted plastic posts - about as cheap as you can make it - typical of this date.