Two Casios, One Keyboard ...and a digital sequencer.

I've always wanted to try making sounds using two Casio MT-240s.

The problem was that two whole synth systems with ROM-bends, clock mods, etc, would be all around too wieldy. They needed to be integrated into a single system, with a single keyboard and a single ROM-bending setup. The solution ended up being a sequencer circuit, a microcontroller, and a repurposed DX7 keyboard.

The Casio MT-240 doesn't care what's connected to it as long as it gets a keyboard-like signal input.

A microcontroller, and a little bit of extra circuitry, can definitely generate the type of pulse that looks like pressing a key on the keyboard. The challenging part is knowing when the pulse should happen. Another circuit is needed, which essentially synchronizes the microcontroller with the MT240's built-in keyboard-scan cycle.

How to control the microcontroller?

Now that the uC can simulate key-presses on the MT240, we need a way to actually choose which notes to play. We need a keyboard- we don't actually want to get rid of the keyboard-ness of the synthesizer as a musical instrument. The uC can do its own key-scan of a separate keyboard (repurposed from a Yamaha DX7), independent of the MT240's key-scan. Replacing a keyboard with another one may sound contrived, but because notes arrive at the uC first, this ultimately means we can manipulate them in code before hitting one or more MT240s.

A digital sequencer?

Notes stored in code also unlocks the capacity to pre-program notes to send to the MT240- a digital sequencer. This is close to what midi software can do, but since this gets to the hardware, the delay between note events can be frame-perfect.

Dual Casio MT240s!

Because of the hardware-ness of the system, the microcontroller can output notes to a second MT240 unit (and possibly more) with near-perfect synchronization. With some programmable controls, you can choose to play both MT240s simultaneously or separately. This is particularly useful for playing circuit-bent sounds, because it means you can load up and control patches differently on either machine with one keyboard.

The combined keyboard-sequencer, function menus, and some grand ideas.

Configuring the keyboard-sequencer system is just a matter of having some sort of interface. I built a little rotary-dial and display for the purpose of being able to simply program/ configure the system with live performance in mind. Right now, you can choose just a few menu options: 00X chooses a sequence to play, 01X chooses a tempo for the sequencer, 02X lets you route the keyboard to either Casio or both. Here are some other grand plans for the future:

• Keyboard modes: latch, tap, hammer
• Arpeggiator: playing a key sequences other notes
• Note remapping: split keyboards between Casio A and B
• Vocoder (possibly)
• Record notes to playback, maybe with a small piano-roll program
• Circuit-bend trigger controller

Thanks for reading!

After half a year, the core system is stable, but the project is onoing. The question now is if this circuit can work with other synthesizers too. If you're interested in using this in your own project, feel free to contact me at bernhardtayang{at}gmail.com