fjo@ttrdf.UUCP (Frank Owen ) (12/28/88)
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 hardware, and should be a snap to build. Is this correct? I think the cheapest commercially availible interface runs about $80. That's not an astronomical amount of money, but if I could make one myself for, say $20 and a couple hours of assembly time, I could use the money saved for other toys. Any info, or pointers in the right direction would be appreciated. Frank Owen (fjo@ttrdf) 312-982-2182 AT&T Bell Laboratories 5555 Touhy Ave., Skokie, IL 60077 PATH: ...!att!ttrdf!fjo -- Frank Owen (fjo@ttrdf) 312-982-2182 AT&T Bell Laboratories 5555 Touhy Ave., Skokie, IL 60077 PATH: ...!att!ttrdf!fjo
henges@ingr.com. (John Hengesbach) (12/31/88)
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
nick@lfcs.ed.ac.uk (Nick Rothwell) (12/31/88)
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 >hardware, and should be a snap to build. Is this correct? I have a MacDrawing of a MIDI interface for the Mac, originally by Kirk Austin of MacTutor, I think. It has a dozen, perhaps 20 components. Doesn't look too difficult- except that I know nothing about electronics, so I'll have to ask my dad. (just kidding...) Shall I post a BinHex'ed form of the MacDrawing? >Frank Owen (fjo@ttrdf) 312-982-2182 Nick -- Nick Rothwell, Laboratory for Foundations of Computer Science, Edinburgh. nick@lfcs.ed.ac.uk <Atlantic Ocean>!mcvax!ukc!lfcs!nick ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ...while the builders of the cages sleep with bullets, bars and stone, they do not see your road to freedom that you build with flesh and bone.
sp@killer.DALLAS.TX.US (Steve Parker) (01/03/89)
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 > hardware, and should be a snap to build. Is this correct? Yea, pretty much. The one I made cost me only about $10 since I had a few scrap parts. The only trick is you have to pump a 500k/1M/2M (depending on software) clock signal back into the ext clock line, since there is no way to divide the internal clock in the SCC to get 31.25k baud. Also, you DO have to use those pc900 optos on the inputs, garden-variety optos are simply not fast enough. I think there was an old issue of Dr. Dobbs (not positive) that had a schematic for a mac interface in it. If you write me (and aren't in a hurry) I can try to dig up the exact reference. - Steven Parker (sp@killer.Dallas.TX.US)
czei@accelerator.eng.ohio-state.edu (Michael S. Czeiszperger) (01/03/89)
In article <6636@killer.DALLAS.TX.US> sp@killer.DALLAS.TX.US (Steve Parker) writes: >[...] The only trick is you have to pump a 500k/1M/2M (depending on >software) clock signal back into the ext clock line, since there is no way >to divide the internal clock in the SCC to get 31.25k baud. Also, you DO I built mine with a 500kHz clock, but later changed it to 1MHz because of compatibility problems. Yes, you would think Mac MIDI software should be able to handle all three clock speeds, but in practice, the default is *always* 1MHz, and some software doesn't support anything else. If you're building your own, save yourself some hassles and use a 1MHz clock. -- Michael S. Czeiszperger | "milihelen: The amount of beauty required to launch Systems Analyst | a single ship." The Ohio State University | 2015 Neil Ave, Columbus, OH 43210 ARPA:czei@icarus.eng.ohio-state.edu PAN:CZEI (614) 292-0161
englandr@phoenix.Princeton.EDU (Scott Englander) (01/05/89)
In article <12456@dcatla.UUCP> dlmnm@sunc.UUCP (Michael N. Moran) writes: >On a related topic, I'd like to know if there is a "correct" way to >setup a serial port to use external clocking. I could muck with the >serial chip directly but ... the implications make me shudder. There is a line on the Mac serial port called HSKi or TRxC, which you can use to feed in an external clock signal. You need to use an interface chip to convert TTL to bipolar signals, of course. -- - Scott
waksman@eniac.seas.upenn.edu (Adlai Waksman) (01/22/89)
In article <12456@dcatla.UUCP> dlmnm@sunc.UUCP (Michael N. Moran) writes: >On a related topic, I'd like to know if there is a "correct" way to >setup a serial port to use external clocking. ... Most MIDI software expects a 1 MHz external clock on the Mac's HSKi line (also called Ext Clk or TRxC; pin 2 on the Mini-DIN 8-pin serial port, or pin 7 on the pre-Mac Plus DB-9 serial port). This is not a TTL clock; it must swing both above and below 0 volts. To convert a TTL clock signal (0-5v) to a bipolar one, Kirk Austin's method from his October 1985 MacTutor schematic has worked for me. Couple the signal capacitatively: /------------o to Mac HSKi (-2.5 - +2.5v) 1MHz TTL clock ----||---+ 0.1uF \---/\/\/---+ 1K _|_ GND (Mini DIN #4, DB-9 #3; /// and TTL circuits' ground) ___________________________________________Adlai Waksman(@eniac.seas.upenn.edu) ...The Universe is thronged with fire and light, And we but smaller suns, which, skinned, trapped and kept Enshrined in blood and precious bones, hold back the night. (Ray Bradbury)