MIDI Interface For NeXTcube Plugs Into The Past

May 16, 2023 by Donald Papp 21 Comments

[Joren] recently did some work as part of an electronic music heritage project, and restored an 80s-era NeXTcube workstation complete with vintage sound card, setting it up with a copy of MAX, a graphical music programming environment. But there was one piece missing: MIDI. [Joren] didn’t let that stop him, and successfully created hardware to allow MIDI input and output.

The new panel provides all the connectors necessary to interface with either classic MIDI devices, or MIDI over USB (where it appears as a USB MIDI device to any modern OS.)

Interestingly, the soundcard for the NeXTcube has an RS-422 serial port and some 8-pin mini DIN connectors. They are not compatible with standard MIDI signals, but they’re not far off, either.

To solve this, [Joren] used a Teensy developer board to act as an interface between classic MIDI devices like keyboards or synthesizers (or even not-so-common ones like this strange instrument) while also being able to accommodate modern MIDI over USB connections thanks to the Teensy’s USB MIDI functionality.

A metal enclosure with a 3D-printed panel rounds out the device, restoring a critical piece of functionality to the electronic music-oriented workstation.

MIDI as a protocol isn’t technically limited to musical applications, though that’s one place it shines. And just in case it comes in handy someday, you can send MIDI over I2C if you really need to.

Reverse Engineering The NeXT Computer Keyboard Protocol

January 26, 2022 by Lewin Day 22 Comments

The NeXT computer was introduced in 1988, with the high-end machine finding favor with universities and financial institutions during its short time in the marketplace. [Spencer Nelson] came across a keyboard from one of these machines, and with little experience, set about figuring out how it worked.

The keyboard features a type of DIN connector and speaks a non-ADB protocol to the machine, but [Spencer] wanted to get it speaking USB for use with modern computers. First attempts at using pre-baked software found online to get the keyboard working proved to be unreliable. [Spencer] suspected that the code, designed to read 50 microsecond pulses from the keyboard, was miscalibrated.

Some analysis with an oscilloscope and logic analyzer allowed [Spencer] to figure out the keyboard was communicating with pulses ever 52.74 microseconds, corresponding to a frequency of 18.960 kHz, sending two 9-bit messages at a time. Disassembling the keyboard confirmed these findings – inside was a 455 kHz clock, with the keyboard sending a signal every 24 ticks producing the 18.960 kHz output.

Reworking the initial code found online to work with the actual pulse widths coming from the keyboard got everything humming along nicely. Now, [Spencer] has a nice vintage keyboard with excellent feel that reliably works with modern hardware. We’d call that a win.

If you need more of a fix, be sure to dive into Keebin’ with Kristina, a regular column all about our favorite tactile input devices!