[Ken Shirriff] completely reverse engineers the 1974 Sinclair Scientific calculator

Wow. Seriously… Wow! The work [Ken Shirriff] put into reverse engineering the Sinclair Scientific is just amazing. He covers so much; the market forces that led [Clive Sinclair] to design the device with an under-powered chip, how the code actually fits in a minuscule amount of space, and an in-depth look at the silicon itself. Stop what you’re doing and read it right now!

This calculator shoe-horned itself into the market when the HP-35 was king at a sticker price of $395 (around $1800 in today’s money). The goal was to undercut them, a target that was reached with a $120 launch price. They managed this by using a Texas Instruments chip that had only three storage registers, paired with a ROM totaling 320 words. The calculator worked, but it was slow and inaccurate. Want to see how inaccurate? Included in the write-up is a browser-based simulator built from the reverse engineering work. Give it a try and let us know what you think.

Now [Ken] didn’t do all this work on his own. Scroll down to the bottom of his post to see the long list of contributors that helped bring this fantastic piece together. Thanks everyone!

[Thanks Ed]


Programmable scientific calculator watch

When the band support on [David]’s Casio CFX-400 Scientific Calculator Watch finally broke after 10 years of use, he found it almost impossible to find another watch with the same functionality. Like any good engineer, [David] decided to design a watch to meet his needs. The result of his endeavors was the µWatch, a programmable watch based on a PIC24 with both RPN and Algebraic calculation modes. The watch runs open source software and is expandable thanks to a serial port, an ICSP programming port, and a spot for an infrared LED on the board. On his site, [David] shows how he made the first µWatch and offers kits for anyone who wants to build their own. We’ve been told that the next batch of kits will be made available in 1-2 weeks and are expected to sell out fast.

[Thanks Tomesz]