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This page was developed in conjunction with a magazine article in the October 2000 edition of NUTS & VOLTS magazine on a unique MIDI musical instrument called the XYLOTRON. This site contains information that was too bulky to include in the article. A XYLOTRON that doesn't need to be connected to a computer to play music? Check out the XYLOTRON II.

Do you need a XYLOTRON brain? Preprogrammed 16F877 chips are available for $20USA (a 20% price reduction!) at the email address below. XYLOTRON building instructions can be emailed for $3US. Be sure to specify XYLOTRON or XYLOTRON II.

The XYLOTRON is a MIDI acoustic instrument that is designed so that anyone can build it. While the HARPSITRON required excellent electronics and woodworking skills, the XYLOTRON can be built by anyone who has built electronic kits and has a power saw. The XYLOTRON is in many ways a simplification of the HARPSITRON design. For example:

1. There are two circuit boards instead of five. Three driver boards and the power supply board were combined into one larger circuit board in the XYLOTRON.
2. There are 25 actuators instead of 30. Reducing the number of actuators allowed me to reduce the number of circuit boards.
3. The actuator mechanism is simpler. The elaborate plucking mechanism in the HARPSITRON was replaced with a simple beater mechanism in the XYLOTRON.
4. The XYLOTRON uses an existing instrument as the sound generator. The XYLOTRON is based on modifying and automating a 25 key Xylophone which can be obtained for about $28.
5. LED indicators for each note were eliminated. This could be added very easily to the driver circuit but based on the HARPSITRON, the feature is not really needed with the power on test and the visual feedback of the key motion.

As a result of the simplifications the XYLOTRON can be built for less than $150. The XYLOTRON still performs a power on test when starting and decodes MIDI data from a MIDI keyboard or computer in the same way as the HARPSITRON.

The driver/power supply board contains the 25 driver circuits and the non-transformer parts of the power supply. The PIC board contains the brains of the XYLOTRON which decodes the MIDI data and sends control signals to the driver board. Solenoid coils were wound on a homemade jig. The solenoid actuator assembly contains solenoids that are activated by the driver board outputs. The actuators hit the bottom of the XYLOTRON keys causing the note to be played. The xylophone can be removed to provide access to the solenoid actuators. The power cord, MIDI cable and power switch are located at the back of the XYLOTRON. The finished XYLOTRON is portable ( I couldn't resist adding a little marquetry).

The circuit boards patterns are in EASYTRAX/EASYEDIT format. The software for the PIC16F877 is in MICROPIC assembly language. With this information and the magazine article you too can build your own XYLOTRON.

The original XYLOTRON used a slightly modified 25 note xylophone (glockenspiel). The modification was that some of the bracing structural material was removed from the bottom to allow the actuators to hit the keys from beneath. Since the actuators fall back to their resting place via gravity, this seemed an optimum solution.

One of the big disadvantages to this arrangement was that the structural members beneath the keys blocked the view of the actuators doing their thing. Part of the fun of the XYLOTRON is watching the precision way in which the keys are struck under computer control. The new design moved the keys from resting on the structural members to being suspended from the structural members. A view of the new frame from from the bottom. and the top. The observer now has an unimpeded view of the actuators and the keys from the front and back of the XYLOTRON and can easily see which key is being struck.

The original XYLOTRON design did not have the ability to play music unless it was connected to a computer and MIDI data was being downloaded in real time. The XYLOTRON II has the ability to "hear" a MIDI tune one time and remember it and play it on command without being connected to a computer. There were no changes to the solenoids or solenoid driver board as described in the October 2000 NUTS&VOLTS. All the changes were made on the microcontroller circuit board and in software. The hardware changes to the XYLOTRON consisted of some rewiring, the addition of a serial EEPROM and two input switches to control the mode of operation. The additional cost was less than $5.00. The XYLOTRON II article was published in the September 2001 issue of NUTS&VOLTS. Reprints of both XYLOTRON articles are available here.

The XYLOTRON III is built into an oak cabinet. The XYLOTRON III has the keys mounted vertically and uses commercially available solenoids from www.mpja.com. The doors open to reveal the actuators and circuit boards. The new XYLOTRON actuators consist of commercially available solenoids and small wooden mallets. The X3 is more fun to watch play because now the keys are hit by small arms. There are twenty five notes in the XYLOTRON III. The back of the unit reveals the MIDI in, MIDI out, and power switch. The new design also has one redesigned circuit board that holds all microprocessor and driver circuits. The driver circuit has been simplified. Commercially made circuit boards are available at the email address below.

The XYLOTRON can play any standard MIDI file which uses MIDI channel 1. The range of the XYLOTRON is from MIDI note 48 to 72 (C4 to C6). Several Cakewalk Application Language (CAL) programs are available to help arrange MIDI files to play properly on the XYLOTRON. The steps are as follow:

1. Use the RANGE.CAL program to determine the highest and lowest note in the MIDI file.
2. Use the transpose feature of CAKEWALK to shift the highest note in the file to 72.
3. Use the ARRANGEX.CAL program to shift notes below 48 into the 48 to 72 range.
4. Because the XYLOTRON must hit a key and not hold the beater against the key, use the SHORTNER.CAL program to shorten all notes to a constant length.

All these programs are available for free. Now your song is ready to play on the XYLOTRON. For some songs already arranged for the XYLOTRON, click here.

Since publishing the XYLOTRON article in the October 2000 issue of Nuts & Volts, the XYLOTRON circuitry has been used to MIDI enable and automate a number of musical instruments including a harpsichord, a calliope and a pipe organ.