Casio Root-8S

		Home New Stuff Author Links Guest book Web-log	Adverts Bric-a-brac Calculators Components Ephemera Events	For Sale Glossary History Hit or Miss Radios Transport	Ultra Vales Wanted Metal Puzzles Articles Clocks

Calculators: Handheld: Casio Root-8S

		Size (approx):	80mm x 150mm x 43mm (w,h,d) Weight 232g excluding batteries
		Power:	6V DC, 4 x AA size batteries. Also accepts adapter (use AD-4145, 1.3W, centre negative) through a socket on the top side three quarters to the left. A red ribbon pull aids battery removal form the compartment. The on off switch is on the left hand side with a red "on" indicator on the dust cover.
		Case:	Bulky solid case made from a three piece dark grey and off-white patterned plastic case. One dark grey piece serves as the display and keyboard escutcheon. Within this, above the display is a silver painted sunken embossed area for the brand and model number. The red plastic display filter is tilted and has white printed text for the extra indicators. The large keys are long travel with a prominent hollow click on depressing and release. The constant switch sits in its own recess with a labelled dust cover.
		Display:	8 digit red LED (individual bubble lens) with two discrete pin-point red LEDs for negative and error indication
		Features:	4 function calculator with square roots, switched constant. Arithmetic (semi-RPN) input
		Age:	1974
		Manufacturer:	Casio Computer Company Ltd, Made in Japan. Serial number inside battery compartment 1074624 and another on the insider of the cover 2181006.
		Comments:	One of the few LED Casio calculators with a sturdy build reminiscent of the horizontal models like the Casio Mini Memory. The logic is not bad for its age and only let down by lack of recovery despite the archaic operation. The original cover is soft black plastic with flip over top flap and double front double-popper closing. It has a right hand black plastic carry strap and is embossed with "Casio" on the front and "Made in Japan" on the back.

Components:	1 x cpu: Texas Instruments TMS0126NC 7401 (January 1974 date code), 28 pin DIL, 0.6" width black plastic 2 x 4 digit LED modules with red bubble lenses 2 x individual red LEDs 17 x transistors 9 x diodes 0 x capacitors 25 x resistors 4 x resistor arrays Secondary board: 5 x transistors 1 x bridge rectifier: Fuji NF113 5 x diodes 10 x capacitors 12 x resistors 1 x transformer module; Fuji MCT 0624 4B-12 (date code February 1974)
Boards:	The keyboard assembly is fixed to the main board (8X-1A) that sits face up, just about filling the whole case. It sits loose on top of the battery compartment and secondary board (8X-2A) underneath. They are joined by six string wires and separated by a card insulator. The display has its own mini-board held in place by the connecting wires and two protruding screws.
Construction:	Remove the screw from the top rear edge. The front section will then lift off easily, hinging from the bottom edge.

Logic comments:	The (C) button is used to clear last entry of a number and (AC) to clear the whole calculator
	Overflow on number input is not suppressed, keying in a ninth digit causes the "E" LED to light but you can carry on calculating with the error state in place
	The logic is semi-RPN (algebraic) with the (-) key actually being a (-=) key: to do 6-2 key in (6)(+=)(2)(-)
	An overflow error shows the result and the "E" LED lights in the far right and is not recoverable
	Divide by zero results in an "E" only in the far right (first) digit which is also not recoverable
	There is switched constant all multiply and divide in the [K] position, whilst [N] is the normal operating mode. When on the first number is the constant in multiply mode, the second in divide mode.
	Negative numbers are flagged by an "-" LED in the far right thereby allowing full eight digit negative numbers
	Negative square roots are not allowed, show the result and the "E" LED lights which is not recoverable
	No other bugs found

With the front removed you can see that the keyboard assembly is on the main cpu board along with the display and display driving transistors. Loads of discrete components is typical of this early portable calculator date. The two 4-digit LED modules and two individual LEDs are mounted on their own angled mini-board, which hides a row of resistors.

This board hides a half-sized board underneath with the equally dense power circuitry.