wilts@cavax.ab.ca (Ed Wilts) (09/01/89)
>>I need a MIDI interface and found an old schematic for one that >>someone designed -- 1 IN, 2 OUTS, 1 THRU. It consisted only of a few >>hex-inverters, an opto-isolator and some resistors. I realize that >>because of the Amiga's UART not a whole lot more is required, but can >>this possibly be all that needed? >> >>Or, should I buy one somewhere? > >The latest Amiga Transactor (September, I believe), has MIDI >interface specs for ALL Amigas. It also has specs for building >a box that will split the signals comming into the box into 5 (or so) >signals comming out. You can also find the schematic in a very old Amazing Computing, a back issue of Electronic Musician and the latest (1.7) of AmigoTimes. I recommend that if you build one if you're up to a little electronic hacking. The only thing I strongly suggest is that you add a switchable RS232 pass-thru so that you can switch to a modem without powering down. Because all the schematics I have seen so far take their power from the Amiga's serial port, you can NOT replace the MIDI interface with your modem cable and get away with it very often. That's how I blew up my first one :-( The Amazing Computing schematic included the pass-thru as well as support for two inputs - this is very handy if you have > 1 keyboard or have 1 keyboard and a sound box (such as a D-110, FB01, TX81Z, etc) that supports an editor/ librarian. Sure beats switching cables... it has two outs and a thru and automagically switches the outs to thrus if you switch the box to RS232 thru instead of MIDI. If you're really energetic, add an external power supply instead of drawing from the Amiga. It'll be a little easier if you ever upgrade to a 500/2000. Base it on the 74LS04 instead of a LM339 and you only need a +5 signal (and no -5) and you can easily generate this from a cheapo wall transformer from Radio Shack pumped through a 7805 voltage regulator. Enjoy! .../Ed (Wilts%CaVax.AB.CA@UncaNet.Bitnet) Ed Wilts Sr. Systems Analyst, Canadian Occidental Petroleum Ltd. Calgary, Alberta, Canada (403) 234-1007
scott@edson.ee.UAlberta.ca (Scott Stephens) (09/02/89)
In article <22969@louie.udel.EDU> wilts@cavax.ab.ca (Ed Wilts) writes: > >>>I need a MIDI interface and found an old schematic for one that >>>someone designed -- 1 IN, 2 OUTS, 1 THRU. It consisted only of a few >>>hex-inverters, an opto-isolator and some resistors. I realize that >>>because of the Amiga's UART not a whole lot more is required, but can >>>this possibly be all that needed? > >You can also find the schematic in a very old Amazing Computing, a back > >from the Amiga. It'll be a little easier if you ever upgrade to a 500/2000. >Base it on the 74LS04 instead of a LM339 and you only need a +5 signal (and >no -5) and you can easily generate this from a cheapo wall transformer from >Radio Shack pumped through a 7805 voltage regulator. > >Enjoy! > > .../Ed (Wilts%CaVax.AB.CA@UncaNet.Bitnet) >Ed Wilts >Sr. Systems Analyst, Canadian Occidental Petroleum Ltd. >Calgary, Alberta, Canada (403) 234-1007 The Amazing Compute article was in Vol. 2 # 2, I built it and it works just fine. I'd use a 74LS14, rather than a 7404, because of the Schmitt triggers, but since these parts will not go to negative voltages, are you SURE it will drive the Amiga input and the inputs to the Synths???? Also the only schematic I've got for an LM339 shows an inverting output on output 3 (this from a Motorola data book), and this should be used to drive the RS232 line to the Amiga (I can't remember whether I actually checked this or not, but the worst that would happen would be driving the Amiga with inverted data). R. Scott Stephens