Homemade MIDI interface for the Atari 8-Bit¢ -------------------------------------------¢ Parts List:¢ 1 7404 TTL Hex Inverter OR 7400 NAND gate¢ 2 220 ohm resistors (10%)¢ 1 Atari serial port plug for your computer¢ 2 5-pin Midi plugs (RCA) for your midi keyboard¢ 1 breadboard/experimenter perf board¢ 1 project case¢ approx. 10 ft. of 3 wire cable ¢ twist ties to tie down wires etc..¢ ¢ ¢ The serial port pins as seen on the computer are:¢ ¢ 2 4 6 8 10 12¢ o o o o o o ¢ o o o o o o o¢ 1 3 5 7 9 11 13¢ ¢ 1 - Clock In 7 - Command¢ 2 - Clock Out 8 - Motor Control¢ 3 - Data In 9 - Proceed¢ 4 - Ground 10 - +5V¢ 5 - Data Out 11 - Audio In¢ 6 - Ground 12 - +12V 13 - Interrupt¢ ¢ For this project, we will only need to use pin #'s 3,4,5, and 10 of the¢ serial port.¢¢¢ ---------------¢ (CRUDE) Ground (pin 4)¢ SCHEMATIC: 7404 |¢ |\ |\ 2| ¢ | \ | \ 220 ohm 5 o 4¢ data out ---| O--| O---\/\/\/---------o o---/\/\/\/-- +5 (pin 10)¢ from computer | / | / 3 o o 1¢ (pin 5) |/ |/ MIDI OUTPUT cable to synth ¢ ¢ 2¢ 5 o 4¢ Ground---o o------------(optoisolator)------- data in to computer¢ 3 o o 1 (pin 3)¢ MIDI INPUT cable¢ from synth¢ ¢ Pins 1,3 of the Midi Output cable and pins 1,2,3 of the Midi Input¢ cable are not connected.¢ ¢ The optoisolator is optional, although it is recommended for extra¢ protection for your midi keyboard. I have used the interface ¢ hard wired without the optoisolator without any problems (so far).¢ ¢ Also note: the normal serial i/o to the disk will sometimes interfere¢ with the midi interface and vice versa. This sometimes results in ¢ a note sounding on the synth when loading or saving a file, or the¢ disk will glitch if you try playing the keyboard during disk i/o.¢ One possible way to remedy this annoying problem is to replace¢ the 7404 with a tri-state buffer which can be turned to a high-Z state¢ using the motor control (pin 8) from the serial port. ¢ ¢ Anyway, BE CAREFUL and check all your wiring before you hook the ¢ interface up to the synthesizer. ¢ ¢ Please let me know if you have any suggestions for improving the ¢ interface.¢ ¢ next:: BASIC Midi Recorder Program¢ New & Improved Assembly Source Code¢ ¢ ---------------------------------------------------------------¢ Christopher Terpin¢ terpin@autarch.acsu.buffalo.edu¢ ¢ News-Disk Editor's note: As with all projects of this nature,¢ I can't be held responsible if something goes wrong. You're on¢ your own! Good luck!¢¢ NOTE: I didn't have enough room to put the M/C source code on this¢ issue, so I'll put that on issue 10. The Basic MIDI recorder is on¢ this issue called MIDI.BAS.¢
