Joe Rounceville has been designing and building peripherals for the Model I which he wants to share with everyone.
First is TRS80HDD. It is a way to run TRS-80 Model I disks from a SD card. Similar to a MISE but far less sophisticated. Schematics, instructions, and background can be found on his GitHub repository https://github.com/calphool/TRS80HDD. He advises that all parts are currently attainable at Mouser Electronics, the edge adapter from DigiKey, and the schematics can be sent to allpcb.com for creation of a PCB.
Second is TRS80GS. It is an expander for a TRS-80 Model that includes Texas Instruments video and audio chips to permit the Model I to do color graphics and have 6 tonal voices and 2 drum voices. It also supports Atari/Commodore joysticks. Schematics, instructions, and background can be found on his GitHub repository https://github.com/calphool/TRS80GS.
Thanks for keeping the TRS-80 alive, Joe!