The first microprocessors were not available when HP started this design, so the entire processor was done at the gate level.
BOWMAR ENGINEERING CALCULATOR SERIAL
But even more complicated is the serial processor architecture of the calculator. In a complex orchestra of multiplexed switches, they steered current through inductors and LED segments, storing energy temporarily and eliminating the need for inefficient dropping resistors. There are many novel concepts in the design, and delves into two of them in his presentation. Early LED devices were a drain on batteries, and HP engineers came up with a clever solution. The HP patent ( US Patent 4,001,569 ) contains an extremely detailed explanation of the calculator in nearly every aspect. In this presentation he walks us through the history of the calculator design and his efforts in understanding and eventually replicating it using modern FPGAs. eventually decided to embark on a three year long reverse-engineer journey that culminated a recreation of the original design on a protoboard that operates exactly like the original from 1972 (although not quite pocket-sized). The more he read, the more engrossed he became.
Since then he gradually developed a curiosity about these old calculators and what made them tick. has long been a fan of HP calculators, and used an HP-41C for many years until it wore out.
It was quite the engineering feat, since equivalent machines of the day were bulky desktop affairs, if not rack-mounted. Fifty years ago, Hewlett-Packard introduced the first handheld scientific calculator, the HP-35.
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