Sinclair Executive was the world's first
pocket calculator, launched
in August 1972 at a price of £79.95 + VAT.
The advert described
it as being "as thick as a cigarette packet",
reflecting Clive Sinclair's stated belief that
"One must always bear a packet of cigarettes
in mind as the ideal size"; it was a running
joke at Radionics that Sinclair, who smoked 40
cigarettes a day at the time, designed everything
to be the size of a packet of 20.
By modern standards, the Executive
was astoundingly limited: it had an eight-digit
display and could add, subtract, multiply and
divide - no other functions. It had automatic
squaring, reciprocals and a choice of fixed or
floating decimal points. Inside the case were
22 transistors, 50 resistors, 17 capacitors and
the piéce de resistance, the Texas Instruments
GLS 1802 integrated circuit, which the advert
described breathlessly as "an electronic
marvel... the largest ever produced for commercial
The Executive was seen as a
genuinely revolutionary advance (which in truth
it was). Calculators prior to the Executive had
been bulky, desk-bound affairs, often depending
on mains power. The fundamental problem was the
high power demands of the LED display: indeed,
it was precisely that problem which drove the
development of liquid crystal displays and ultimately
killed off the LED-equipped calculators.
The advert for the Executive
highlighted this problem, though it was a little
disingenous about how Sinclair had resolved it:
But the real
genius lies in the circuitry linking the brain,
the batteries, the keyboard and the display.
Circuitry soaks up power, which is why other
pocket calculators have to use large batteries
- and that, in turn, makes them bulky.
In the Executive,
the Sinclair flair for miniaturisation has developed
circuitry which absorbs virtually no power.
Tiny hearing-aid batteries take up the minimum
space and, used from time to time during the
day, will last for several weeks.
In fact, what Sinclair had done
was to exploit the persistence of the diode displays
and the chip memory. It was immediately apparent
that continuous demands on the batteries drained
them very rapidly. Jim Westwood, Radionics' chief
designer, discovered that if one disconnected
the power and turned it on again fairly quickly,
the display and the contents of the memory remained
intact. With the transistors built into the circuit
holding up to five seconds of charge, it was a
simple matter to pulse the power on and off. It
reduced the power demand from an unacceptable
350 milliwatts to a barely acceptable 30 milliwatts.
New Scientist explained the process:
"Executive" uses a single metal oxide
semiconductor (MOS) chip containing 7000 transistors.
This type of integrated circuit normally consumes
350 milliwatts of power, provided by a fairly
bulky rechargeable battery. Sinclair's miniaturisation
trick depends on a special circuit which reduces
the power requirement to about 20 milliwatts.
This is accomplished by the elimination of all
resisitors from the circuitry and with a clock
that turns off the power most of the time. Three
small deaf-aid mercury cells provide 20 hours
of life - over four months normal usage.
Power is turned
on only in 1.7 microsecond pulses, a figure
determined by the storage time of a control
transistor. The unit has an oscillator clock
which operates at 200 kilohertz during calculations
and drops to 15 kilohertz between each operation.
Thus shut off time ranges from 3.3 microseconds
during calculations to over 65 microseconds
between. The device relies on the capacitance
of the chips to store information during the
shut off times, and 1.7 micorseconds is long
enough for the chip to carry out a single change
of state of the electronics. Any calculation
can be done in 1000 such changes.
Even so, battery life was only
a few hours and the machine could be physically
dangerous. If it was left on, the batteries had
a nasty habit of exploding and blowing the machine
to bits. One day a telex arrived from Moscow.
A senior Soviet diplomat had been carrying an
Executive in his breast pocket when it exploded,
convincing the unfortunate man and his entourage
that he was suffering a massive heart attack.
After the fuss had died down, investigators found
that he had forgotten to switch the calculator
off: the current drain was so high on the batteries
that they grew hotter and hotter, finally exploding.
Perhaps fortunately, the incident was accepted
as an accident, rather than a capitalist provocation!
Such were the joys of early 1970s electronics.
Such slight mishaps did not
dent the Executive's deserved success, however.
It was virtually the first attractively-styled
calculator, its rivals and predecessors being
utilitarian lumps of plastic. The neat design
of the injection-moulded polycarbonate casing
won its designer, Richard Torrens, the Design
Council Award for Electronics in 1973. New Scientist
described it as "not so much a professional
calculator - more a piece of personal jewellery".
Design magazine called it "at once a conversation
piece, a rich man's plaything and a functional
business machine". It was even exhibited
at the Museum of Modern Art in New York.
The first Executive was
a major success, earning Sinclair over £1.8m
in profits, and was followed up at the end of
1973 with the Executive Memory. This had
the eponymous extra feature and "a new black
and white styling", at a far cheaper price
of £24.95 + VAT.