The Pulsing Power Supply.

Sir Clive Sinclair nearly made the first pocket calculator. HP beat him by three months with its Model 35 launched in July 1972. Sinclair’s calculator, called Executive, launched in October  1972.

One of the problems of making a portable product in pre-LCD days was the power draw of the LED display. Sinclair got round that by using a pulsing power supply.

For Sinclair it was one of his most satisfying inventions, because, he says:  “What we did there was to make an extremely slim one - ours was only nine millimetres thick and everybody else was making great clunky things - much bigger than ours - and we managed to reduce the power consumption by a factor of between ten and thirty times because we could switch the chip on and off without it losing its data, so it was only on for very brief periods. So we got the power consumption right down, so we could run it off these little tiny button cells. Nothing like that existed in the world and so we sold it very well in the US as well as over here."



  1. Thanks for that, Jamo, most interesting. I didn’t know that.

  2. Some of the best ideas are the simplest.
    I had assumed Pico Electronics had designed Sinclair’s first scientific calculator IC and fabbed it on GI’s process (had been told this by one of the designers). Perhaps it was the later versions – the ones that were accurate !

  3. Thanks Mike that’s extraordinary and you could say ‘when journos were engineers . . . . ‘ – Sinclair had no formal engineering training, his first job was journalism.

  4. Loads of details on the algorithms at

    When engineers were real engineers :-)

  5. Yes I think Sinclair was even prouder of the Scientific calculator than he was of the Executive, Mike. Sir Clive recounts: “We did the world’s first single chip scientific calculator – the first cheap one too (it cost under $30). We did that by taking an existing TI chip – which was a four function chip. TI had made it internally programmable – you could change the ROM – but it had only three registers. We reprogrammed that, much to their amazement, to create a full scientific calculator. A friend of mine, Nigel Searle, a computer scientist, did the programming, and I did the algorithms because no algorithms existed at that time which would have worked in just three registers. We went to Texas, stayed in a hotel room, and did the whole job in a few days. We took the programme in to TI and then went back and collected the chip. TI were completely baffled by this. There was a chap at London University, a professor who specialised in algorithms, and he couldn’t figure out how it could ever be done in just three registers. He thought it was technically impossible.”

  6. Not sure about the Cambridge Phenomenon as that embraces far more than electronics and software, but Clive did kill the slide rule once and for all with the Sinclair Scientific he launched next.

    AND you had to solder it together so you saw the insides in detail.

  7. Yes indeed, SilverMan, but Uncle Clive overcame the problems of his day – one of which was that electronic products in the UK had to have a Thorn, STC, GEC, Bush, Decca, Plessey or some such recognisable label on them. Once Clive broke that taboo there came a plethora of stuff from non-traditional sources – Acorn, Oric, Dragon, Tangerine, Camputer, Newbury et al.

  8. The good old days. Today clive would get tied up with EU red tape and EMC regs and get rather annoyed at the hurdles to bringing any product to market.

  9. Sinclair inspired a lot of people, Paul. Andrew Rickman who founded Bookham, tells how, as a teenager, he wrote to Sinclair to ask for components for a product which had blown up and Sinclair wrote back to him personally. Although some people say Cambridge Consultants fathered the Cambridge Phenomenon, I think it was Sinclair because he was a manufacturer – in fact Sinclair’s sales guy went off to found Acorn which spawned ARM. So Sinclair really started the whole thing.

  10. Oh yes, zeitghost, and in those days you could sit in a field without having anyone phone you up.

  11. Sir Clive was ahead of his time, but he was smart enough to translate many of his innovative ideas into products he was able to sell. I still remember the awe I had as a teenager for the Sinclair ZX Spectrum computer I got with my savings. It was the beginning of a fascination for technology that still lasts to this day.

  12. I remember someone with a rich daddy buying one of those back in the day.

    Long long ago & far far away.

    It was all green fields around here back then.

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