Ken Shirriff (@kenshirriff )

Ken Shirriff

Bio Restored Apollo Guidance Computer, Xerox Alto. Reverse-engineering old chips. Analog computing. Added ₿ to Unicode. Charger teardowns. Arduino IRremote library.
Location Silicon Valley
Tweets 856
Followers 11,3K
Following 770
Account created 06-05-2010 17:53:57
ID 140913803

Twitter Web App : Radio & Nukes During launch/injection and autonomous orbital flight phases, the clock was synchronized to the Program-Timing Control Equipment. It could also be synchronized to the TV unit. A small transformer isolated the external pulses; nowadays, an optoisolator would be used.

Twitter Web App : Llewellyn Pritchard They already had lots of divide-by-10 BCD counters for the clock digits, so my guess is they preferred to use the same chips (similar to the 7490 chip). Propagation delay didn't matter because they just wanted 1 Hertz pulses.

Twitter Web App : Esteban Villalobos We haven't powered up the clock yet, but we plan to. I had to reverse-engineer the power supply to figure out how to hook it up, and then order the obscure Soviet connector from Bulgaria. We'll carefully test the power supply and then hopefully the clock will run.

Twitter Web App : The Soyuz spacecraft used a digital clock on the control panel. Surprisingly complex, the clock had over 100 ICs and a switching power supply crammed inside. I open the clock and explain what all these chips do. Details: righto.com/2020/01/inside…

Twitter Web App : Craig Ah, the LSU connection explains a lot. "Geaux DSC" on the die would be from the phrase "Geaux Tigers". And the building the tiger is jumping from, is that the LSU Tiger Stadium?

Twitter Web App : Trundle Fox The thickness of the layer affects the color. The colors come from interference of different light wavelengths, not from pigmentation. Here's a color chart: fabweb.ece.illinois.edu/gt/gt/gt7.aspx

Twitter Web App : Nice tiger chip art on Dallas Semiconductor wafer from 1987. Interesting NPN/PNP transistor test circuit as well as feature widths from 50 μm down to 1 μm. Id rather be modeling. The 9256 and 2256 part numbers dont match products; maybe this was a development wafer?

Twitter Web App : Fred Temperton Some chips are programmed using tiny fuses, e.g. ROMs, security protection, tuning analog chips. High current is applied to blow the fuses. An anti-fuse is the opposite; it is an open circuit until high current is applied, and then it shorts out.
righto.com/2019/07/lookin…

Twitter Web App : Unusual Dallas Semiconductor wafer is entirely test circuitry, with 20 test blocks repeated over the wafer. Everything from transistors of different sizes to flash memory cells. Not shown: resistors of many types, anti-fuses, capacitors, isolation, and other chip structures.

Twitter Web App : Rue Mohr Computer History Museum And then there are people who advocate 72-character lines. That goes back to Fortran. The reason is that Fortran was developed on the IBM 704 computer (1954), which could only read 72 columns from an 80-column punch card due to its 36-bit words.

Twitter Web App : Alfred Brattain Computer History Museum We do have programs to play Joy to the World and Silver Bells (among other tunes) on the IBM 1401s line printer. By printing characters in the right sequence, the chain bangs out a semi-recognizable tune.
righto.com/2019/09/risky-…