From ucsd!nosc!helios.ee.lbl.gov!pasteur!ames!mailrus!csd4.milw.wisc.edu!leah!itsgw!steinmetz!uunet!ingr!henges Sat Dec 31 04:52:40 PST 1988 Article 3701 of rec.music.synth: Path: ucsd!nosc!helios.ee.lbl.gov!pasteur!ames!mailrus!csd4.milw.wisc.edu!leah!itsgw!steinmetz!uunet!ingr!henges >From: henges@ingr.com. (John Hengesbach) Newsgroups: comp.sys.mac,rec.music.synth Subject: Re: DIY MIDI interface? Keywords: MIDI Message-ID: <3318@ingr.com.> Date: 30 Dec 88 16:05:21 GMT References: <817@ttrdf.UUCP> Reply-To: henges@ingr.UUCP (John Hengesbach) Organization: Intergraph Corp. Huntsville, Al Lines: 99 Xref: ucsd comp.sys.mac:14949 rec.music.synth:3701 In article <817@ttrdf.UUCP> fjo@ttrdf.UUCP (Frank Owen ) writes: > > Has anyone figured out how to kludge up a Do-It-Yourself MIDI interface >for the Macintosh? It seems that the one Apple sells has practically no A reply... 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. >>>>>>> DATA FLOW >>> (MAC TO MIDI INSTRUMENT) >>>>>>>>> +-------+ +------+ To MAC 4 10|26LS32 | |7407 | Serial >------+ |11 1| |2 +------+ 5 Port 5 9| +-----+ +-----+R=220 +-----< \ DB9 pin >------- | | | +------+ \ (5 pin DIN socket) Numbers | | | | | MIDI OUT +-------+ +------+ / (to instrument) +------+ +------+ 4 / +5 volts -+R=390 +--+ +5 volts -+R=220 +-----< +------+ | +------+ +-------+ | +------+1 +------+ 4 8 6|26LS31 | | |MCT2 +-----+R=220 +-----< \ >------+ |11| 5| | +------+ \ (5 pin DIN socket) 9 5| +--+--+ | | MIDI IN >------- | 4| |2 5 / (from instrument) | | +-+ +------------------< / +-------+ | +------+ | v Ground <<<<<<<<<<<<< DATA FLOW << (MIDI INSTRUMENT TO MAC ) <<< +-------+ +------+ 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 resistormay 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. There have also been allowances made for the fact that 80 column ascii displays are not **exactly** graphics terminals. Also note that the MAC pin numbers are for the DB9 connector **NOT** the 8 pin mini-DIN connector!! The age old question of where to get power for this always remains. On the pre-MAC-PLUSs, there was power available from the serial port connector. I solved this problem by finding a 7 VDC AC adapter at a parts store and using a 5 volt voltage regulator IC to bring it down to 5 volts. This is left as an exercise for the student..... The 26LS31 and 26LS32 are the same type of chips which are used in the MAC for RS-42? conversion. I got them from a store in Santa Clara California (Anchor Electronics (408) 727-3693). They also have 1 Mhz Oscillators as well. I have built several variations of this over the last two years and have had good success using a variety of music software with them. John Hengesbach (205)772-1669 uunet!ingr!henges Intergraph Corporation Huntsville, AL 35807