Roger Murley / BYTESHiFT has a developed a recreation of the 26-1145 RS-232 interface board for the Model I
They are available for sale to those who wish to purchase one, or for those who like to build, the Gerbers, schematics, BOM, and KiCAD source files are available on GitHub.
Roger’s design replicates the operation of the original board, ensuring compatibility with existing Model I software. Hardware-wise, he reports a few differences:
- SMT components are used wherever possible, to minimize cost
- Sense switch (DIP switch configuration) functionality is removed, so that the interface must be configured via software
- The TERM/COMM switch has been removed. The unit is configured in TERM (DTE) mode, and an external null-modem adapter must be used if operation as a DCE device is required.
- IC selection eliminated the need for +12/-12/-5 supply rails. +5V is the only supply needed
More info can be found at: https://byteshiftmusic.com/trs-80-model-i-rs-232-interface-re-creation/