Mac Midi Interface

From: ace@tidbits.com (Adam C. Engst) Subject: [*] minimal-midi-interface.txt Date: Sat, 22 May 93 08:24:20 PDT (Oops, I specifically wanted this stored in a /report type directory so that I could refer to it in the final installment of the TidBITS MIDI series. Thanks! :-) -ace) Here's a schematic for creating a simple MIDI interface for the Mac. It's a bit old, from what I gather from the person who sent it to me, and the address may not be valid for the author any more. Of course, I have no idea if these plans work. :-) cheers ... Adam C. Engst, TidBITS Editor MINIMAL MAC--MIDI INTERFACE =========================== Well, here it is all you MIDI fans. THE ultimate in simplicity!! This is a simple schematic for a serial to MIDI converter. There are two functions performed here. One is the conversion from current loop to RS-422. The second function is supplying the 1 MHz signal for the serial chip to sync up with the 31.5K baud rate of MIDI. Macintosh MIDI Serial port 5 pin DIN DB9 pin numbers pin numbers +-------+ +------+ 4 10|26LS32 | |7407 | >------+ |11 1| |2 220 ohm 5 5 9| +-----+ +------/\/\/-------< \ >------+ | | | \ | | | | | MIDI OUT +-------+ +------+ / 220 ohm 4 / 390 ohm +5 volts ---/\/\/-------< +5 volts --/\/\/----+ | +-------+ | +------+1 220 ohm 4 8 6|26LS31 | | |MCT2 +------/\/\/-------< \ >------+ |11| 5| | \ 9 5| +--+--+ | | MIDI IN >------+ | 4| |2 5 / | | +-+ +------------------< / +-------+ | +------+ | v Ground +-------+ +------+ 7 10|26LS31 | |1 MHZ | >------+ |9 8| OSC | 3 11| +-----+ | >------- | | | | | | | +-------+ +------+ Power connections: GROUND +5 ----- -- 7407 7 14 26LS31 8,12 4,16 26LS32 8,12 4,16 OSCILLATOR 7 14 Notes: The optical isolator MCT-2 above can probably be any relatively fast optical coupler. Note that the 390 ohm resistor may need to be adjusted to make sure the output does not saturate. Using a scope while feeding a MIDI signal in should show you whether the signal looks clean. The diagram has been drawn to show MAC signals on the left and MIDI signals on the right. Also note that the MAC pin numbers are for th…