Travis Smith's TeensyROM Adds a Wealth of Functionality to Your Commodore 64 or Commodore 128

Vintage computing enthusiast Travis Smith has designed a new accessory for the classic Commodore 64 microcomputer, and its follow-up the Commodore 128, offering a range of features in a single Teensy 4.1-powered cartridge: the TeensyROM.

"TeensyROM is a ROM [Read-Only Memory] emulator, super fast loader, MIDI Host [and] Device, and Internet interface cartridge for the Commodore 64 & 128, based on the Teensy 4.1," Smith explains of his creation. "Compatable with C64 and C128 machines/variants, NTSC and PAL supported."

At its simplest, the TeensyROM can work as a way to load cartridge ROM images into a real Commodore 64 or compatible, loaded from the Teensy's own flash storage or from a microSD Card or USB storage device. It can also load program files directly, and at a considerably faster speed than official Commodore storage devices like the 1541 floppy drive or Datasette cassette tape deck.

That's only part of the TeensyROM's feature-set, though. The device can also serve as a MIDI input or output, allowing you to make use of the Commodore 64's famous MOS Technology 6581 Sound Interface Device (SID) chip from a USB MIDI keyboard — or to drive an external MIDI device from the Commodore 64 itself. It's also possible to stream MIDI- or SID-format files from a modern PC and hear them played on the original hardware. Finally, the gadget also offers internet connectivity over an Ethernet port — emulating a Swiftlink cartridge with 38.4kbps modem attached.

"I chose the Teensy 4.1 for this project to take advantage of all its external interface capabilities (USB Host & Device, SD Card, Ethernet)," Smith explains. "I also wanted to use its many IO [Input/Output] pins to do 'direct' interfacing so it can be largely software defined."

The TeensyROM has been published to GitHub under the permissive MIT license with full source code, hardware design files, and a 3D-printable case, with Smith saying it was designed for those "medium skilled" at soldering; he is also selling fully-assembled units on his Tindie store for $59.