Larry Cotton’s MIDI Robot Marimba: Update

Over 4 years since Larry Cotton’s “player marimba” was featured in Make and subsequently retrofitted for MIDI using MD24 MIDI decoders, the instrument is still going strong. Larry recently updated the drive circuitry, replacing the original relays with NPN Darlington transistors to drive the mallet solenoids. Video of the marimba in action can be found here and here.

MIDIMarimbaLarry writes:

My MIDI Marimba (which uses 2 of your MD-24’s) is 90% refurbed.

The MD24’s work perfectly, and are more than capable of triggering the TIP-120’s, a vast improvement over relays, etc.

I also added RCA plugs and jacks to the mallets, for easy servicing and assembly/disassembly.

The first pic shows early stages of the new wiring. The power supply’s pretty beefy for the solenoids, with adjustable output around 12V, and 5V for the MD24’s.

The second pic was taken just before all the wires were stuffed in and the plexiglass cover installed.

The third pic shows it all buttoned up. That’s an iRig Keys keyboard on the floor, and an ancient Gateway laptop running Cakewalk software. I’m also using an M-Audio Uno to deliver MIDI to the MD24’s.

The wonderful little iRig Keys allows the marimba to be recorded and played manually. Kids love it.



MIDIMarimbaSystemThe picture below shows an initial test of the MD24 and TIP120 driving one of the marimba’s solenoids. Video here.