The MiniMidi Embedded Music Platform (aka The MidiBoat).

Joshua R. Smith and Josh Strickon

Physics and Media Group, MIT Media Lab

Last updated 3/2/98. For the latest version of this document, see http://jrs.www.media.mit.edu/~jrs/minimidi

Overview

The MiniMidi is a platform for standalone "no-PC" music applications. It has a Crystal Semiconductor CS9236 General Midi wavetable synth, digital to analog converter, preamp, PIC16F84 microcontroller that can run MIDI sequencer or interactive music software, 8K bytes of content EEPROM, and an LED. Its power requirements are on the hefty side: 9V DC at about 500mA. It has connectors for power, stereo audio out, and one for serial command data in. There are eight uncommited bi-directional digital I/O lines with holes for connections to off-board sensors, actuators, or other devices.

The serial-in connector drives pin B4 (pin 10) of the PIC. Pin B5 (pin 11) of the PIC drives the synth input. When the MiniMidi is running interactive music applications (such as the Musical Jacket), the software performs some complicated mapping to turn the sensor information coming through the serial connector to pin B4 into MIDI notes going out pin B5 to the synth. When you simply want to use the device as a synthsizer (generating the MIDI commands from somewhere other than the PIC), there are two methods. The first is to burn code ("midithru.hex") into the PIC that simply replicates the state of pin B4 on B5. The second is to connect directly to the MIDI input. In this case, you should burn code into the PIC to tristate pin B5. (Some users have cut the trace instead...please don't mangle our nice board in this way!)

In addition to the connectors and general purpose I/O holes, there are holes that can be stuffed with a two-pin .1" Molex connector if desired. The connector should be stuffed vertically (see figure) to duplicate the function of the serial command data in connector. In this configuration, the top pin is ground, and the bottom pin is the serial data in. The hole to the right of the serial data in pin is connected directly to the synthesize input. If you want to drive the synth directly from an off-board MIDI source, connect here, but remember to tristate pin B5 (pin 11) of the PIC to prevent contention on this line.

PIC pin assignments

Pin 1 PIN_A2 A2---uncommitted digital I/O

Pin 2 PIN_A3 A3---uncommitted digital I/O

Pin 3 PIN_A4 A4---uncommitted digital I/O

Pin 4 MCLR

Pin 5 VSS (GND)

Pin 6 PIN_B0 LED---LED!

Pin 7 PIN_B1 B1---uncommitted digital I/O

Pin 8 PIN_B2 B2---uncommitted digital I/O

Pin 9 PIN_B3 B3---uncommitted digital I/O

Pin 10 PIN_B4 KBDIN---"Keyboard in"

Pin 11 PIN_B5 MIDIOUT---Midi out

Pin 12 PIN_B6 TX---uncommitted digital I/O

Pin 13 PIN_B7 RX---uncommitted digital I/O

Pin 14 VDD (+5V)

Pin 15 OSC2

Pin 16 OSC1

Pin 17 PIN_A0 EECLK---EEPROM clock line

Pin 18 PIN_A1 EEDATA---EEPROM data line

Example Code

Warnings, Tips, etc

Don't run the MiniMidi at more than 9V. The synth we used is a 3.3V device, and at the currents drawn by the synth, the regulator that drops the voltage down to 3.3V overheats if its input is more then 9V.

If you want to drive the synth directly (rather than from the on-board PIC), remember to tristate pin B5 (pin 11)...contact us if you're not sure how to do this. Please don't cut the trace!