I am looking for information on "Expanders", which were built to allow TI85, TI86, TI92 users to store programs & other data externally in an era before USB Flash drives, I built one for my TI85 & TI86 in 1999 / 2000, the Expander II was only capable of storing up to 1MB! On an Atmel EEPROM IC, it also required an on calc program to facilitate it's function, it was a voluntary project in an Industrial Electronics course, I had to etch the PCB myself & mail ordered a programmed microcontroller needed to read / write to the EEPROM IC & communicate with the calc. I am wondering if there is documentation on, particularly, the "Expander II" / "Expander 2", schematics, microcontroller code & other docs. I'm wanting to build another "Expander II" as a vintage hardware project. I own a PICKit3 programmer / debugger so programming a microcontroller is trivial, likely would use a PIC16F887 or PIC16F877a Microcontroller, I have DOZENS of them on hand.

Looks like http://web.archive.org/web/20010803043426/http://horizon.pair.com/e2/plans.html has the schematics

Also, this topic has more info: https://www.cemetech.net/forum/viewtopic.php?t=5587&start=0

Adriweb, thank you for the links, one of the links brings back many memories as it's the one I used to build my Expander II even ordering the programmed microcontroller from the reference on that old site.

Apparently I misremembered the Expander II having a PIC microcontroller. I think the first "Expander" utilized a serial EEPROM or Flash based IC & I've come across references indicating the use of a "PIC" microcontroller in an early variation of "Expander".