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Sinclair Executive
and
Sinclair Executive Memory

Sinclair Executive

Type 1

Type 2

Sinclair Executive type 1
Sinclair Executive type 2

Sinclair Executive

Distinctive features: The first "slimline" calculator, the first calculator powered by button cells, the first Sinclair calculator.

Technical details:
There are two known versions of the Sinclair Executive, with different keyboard markings.

Display is 8 digits, red LED.

4-function.

Integrated Circuit: Early models used the Texas Instruments operating in a pulse mode (see information below).
The cut Type 2 model on display at the Science Museum, London, was photographed with a GIM (General Instrument Microelectronics) C550

5.4v (4x button cells).

56 mm x 138 mm x 9 mm (2.2" x 5.5" x 0.4").

Introduced August 1972.

Made in England

The incredibly small thickness for this stage in calculator development was attained by using button cells as the power source.
As explained below, the low power consumption needed to employ button cells with their low capacity was attained by pulsing the electronics - not recommended by the manufacturer, but it worked.
The keypad uses a very thin plastic membrane moulding to keep the thickness down.  The actual keys are the tiny buttons in the centre of each pad area.

Side view

Showing how thin the Sinclair Executive models are.

Batteries

With battery cover removed, showing the four button cells.

Sinclair Executive
Sinclair Executive Type 2 cut to show inside

A Sinclair Executive Type 2 cut to show inside.  Photographed at the Science Museum, London.

The main integrated circuit here is a GIM (General Instrument Microelectronics) C550.

For this period in the development of electronic calculators the Sinclair Executive was incredibly thin, attained by using button cells as the power source.
The low power consumption needed to employ button cells with their small capacity was attained by pulsing the electronics - not recommended by the integrated circuit manufacturer, but it worked.
The keypad uses a very thin plastic membrane moulding to keep the thickness down.  The actual keys are the tiny buttons in the centre of each pad area.

This was the first Sinclair calculator.  It was one of the smallest calculators of the time and certainly the thinnest.

 

The journal "New Scientist" proclaimed in July 1972[1]:
"Just as the price war in electronic calculators was reaching its peak, a Huntingdon hi-fi maker has stepped in with a smaller rather than cheaper unit.  Sinclair Radionics Ltd has produced the first calculator that can comfortably fit in the user's pocket along with his wallet and cheque book.  Sinclair's Executive is only 3/8in thick, smaller than a pound note, and weighs 2.5 oz, which makes it less than one third the weight and volume of the Rapid Data Rapidman 800.   The Executive also has additional functions, including squares, reciprocals, and multiplication or division by a fixed constant.
At 79 [Sterling], the Executive is twice the price of the Rapidman 800.  But Clive Sinclair argues that the "executive toy" market is not particularly price sensitive; the firm has ordered components for 100,000 calculators.
Sinclair's "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 resistors 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 microseconds 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."

 

The journal "Electronics" gave more technical information[2]:
"Using the standard Texas Instrument 1802 MOS calculator chip ...
Engineers at Texas Instruments Ltd. say they've not tested 1802 chips in the particular way that Sinclair is using them, but the only snag they can foresee is that some chips might need more power than Sinclair is giving them to work properly. To guard against this, Sinclair is checking each chip for its working power threshold before use.  Since he offers a five-year guarantee on a machine priced at $205 in Britain, he obviously has no qualms.
The seven-segment gallium-arsenide-phosphide display is driven directly from the batteries and the chip, an approach which avoids the need for buffer amplifiers between chip and display."

 

The cut Type 2 Sinclair Executive on display at the Science Museum in London, shown in the photograph above, uses a different integrated circuit, the GIM (General Instrument Microelectronics) C550 rather than the Texas Instruments TMS 1802 described above.  With the rapid development in electronics around this time the C550 could probably operate within its normal parameters while working at the power required.

 

Clive Sinclair was already well known for his compact and innovative electronics.  This calculator demonstrated his flair with an incredible calculator design for this time.

SinclairExecutive_10

An advertisement for the Sinclair Executive, emphasising how slim it is.

It also explains "The secret of the Sinclair Executive: The Executive's "brain" is an electronic marvel – a 7,000-transistor integrated circuit (the largest ever produced for commercial use)"

Sinclair Executive Memory

Sinclair Executive Memory
Sinclair Executive Memory

Sinclair Executive Memory

Similar to the Executive above, but also has a memory.

Introduced 1973.

Made in England.

Sinclair Executive Memory

Side view showing how thin this machine is.

Click here for more Sinclair calculators.
Also see the article Clive Sinclair and the pocket calculator in the Collecting Calculators section of this site.

 

References:

  1. "Pocket calculators add up to a big market", New Scientist, July 20 1972, p144.
  2. "Pocket calculator weighs in at 2.5 ounces", Electronics, July 3 1972, p3E.

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© Text & photographs copyright Nigel Tout   2000-2016  except where noted otherwise.