| +Home | Museum | Wanted | Specs | Previous | Next |
Master Model H-1 Desktop Calculator
Updated 6/7/2008
This machine appears to be quite unique and
unusual. It was found for me by my aunt at a Seattle-area flea market. She
paid $0.50 for it! I've never heard of or seen another machine like it.
The machine is from the mid-1972 timeframe. It was made by Master Calculator
Co., a division of 6/C Inc, of Grand Prarie, TX. If anyone out there
reading this knows anything about this company and the machines it made,
I'd really love to hear from you. This calculator was also marketed by Smith
Corona Marchant as the SCM F-16, through an OEM agreement with Master Calculator
Co.
Inside the Master H-1 The Master H-1 is a rather unusual
four-function desk calculator. It has a full 16-digit capacity, but only has
an 8-digit display. A special key on the keyboard (a double-ended arrow)
toggles the display back and forth on each press between the most significant
and least significant eight digits of the 16-digit number. It is possible
to enter numbers larger than the eight digits on the display, however, when
entering numbers from the keyboard, the 'toggle' key doesn't work...you end up
entering numbers larger than 8 digits 'blind'. The 'toggle' key only
works with results in the display.
The H-1 uses fixed decimal
point logic, and it took a while to figure out how to set the location
of the decimal point. There is no dial, switch, or other obvious selector
to tell the machine where the decimal point should be located. When the
machine is powered up, the machine is set to no digits behind the decimal
point, making the machine effectively an integer-only calculator.
After poking around for quite some time, I found that pressing and holding
the "CE" key, while at the same time, pressing a digit from 0 to 7
on the keyboard, sets the fixed decimal point location. This is a very
similar method of fixed decimal location to the Marchant
Cogito 412 and
Cogito 414 calculators.
Detailed view of Master H-1 Circuitry The Master H-1 is based on a four-chip LSI chipset made by
Electronic Arrays, Inc., of Mt. View, California. EA no longer
exists, having been bought out by NEC after falling upon hard times in the
late 1970's. The chips are numbered "190B-7010", "280B-7008", "310B-7014", and
"150B-5005". The numbers after the dash in the part number are not
date codes. All of these IC's have date codes with the earliest
being 7148, and the latest 7201. This chipset appears to be an updated
version of Electronic Arrays' first calculator chipset, used in another
machine in the museum, the ICM 816.
The LSI's are all in 24-pin plastic packages. A National Semiconductor
DM8880 chip performs display drive functions. The guts of the machine
(except the power supply transformer) are mounted on a double-sided
fiberglass circuit board, which uses plated-through holes for feedthroughs.
The power supply is a simple transistor-regulated linear supply. The keyboard
uses individual key modules which contain magnet-activated micro-switches.
The keycaps are moulded plastic, with printed-on (rather than moulded in)
keycap legends.
The Display Module The H-1 uses a neon-gas discharge display, similar to a Burroughs
Panaplex, but it is definitely not made by Burroughs. The Burroughs displays
have transparent electrodes deposited on the glass plates, while the
display module used in the H-1 uses a metal mesh screen for the digit grid,
and metal electrodes for the segments. The display is arranged as
seven-segment digits, with a decimal point to the right of each digit.
The display is driven by a combination of the forementioned National DM8880
IC, and discrete transistor drivers. The calculator does not provide
leading or trailing zero suppression. Negative results are indicated by
a very early LED situated to the left of the display. The display itself
glows orange, however, the case has a red filter which is situated in front
of the display modules, making the digits look very much like red LED
digits rather than gas-discharge digits.
Display showing most significant and least significant digits of result of 99999999 X 99999999
The Master H-1 is rather fast machine for its day, and considering that it calculates to a full 16-digits of capacity, it is actually very fast. Sixteen 9's divided by 1 takes less than 1/3 second to complete. Eight 9's times itself results in an almost instantaneous answer, with the most significant digits displayed by default (with no decimal point present), and the least significant digits being displayed by pressing the 'display toggle' key, as shown in the images above.