jer@peora.UUCP (J. Eric Roskos) (02/24/86)
Last weekend I posted a long anecdote about my frustrations in trying to build a MIDI interface for the Macintosh. In response to that, I received a number of suggestions, and I worked again this weekend on it. After building three unsuccessful prototypes, the fourth one worked. I will post the drawings for it in a couple of weeks, after I am fairly sure I don't experience any "blighter blow ups". I feel confident that the interface meets the specs for the line drivers, etc. in the Macintosh, but the Mac has a couple of not-well-documented things in it (i.e., RFI filters in the power supply output and the serial port) which I'm not as sure about. The interface (which is just for DMCS, so it only has an output side, no input) uses 1 1MHz crystal, 1 7404, 1 741, 4 resistors, 2 diodes, and 1 9-volt battery, so it costs around $10, a good bit less than the commercially available ones. Here are the salient parameters, which I didn't have last week: - The clock frequency (for DMCS) is 1 MHz. - The clock pulses have to go between 0V and -5V with respect to the ground pin (pin 1); i.e., the clock is *negative* with respect to ground (finding that out was what took 2 prototypes... plus 2 more to make a driver for the clock input that worked). Thank you to chips@tekchips, arms@alberta, and kahrs@alice for their suggestions. I'll post the drawings in a couple of weeks... I also have one for the IBM PC, if anyone's interested, but it requires a Motorola 6801, since it's really a 9600-baud serial to MIDI buffer/interface (but it goes both ways, input and output, instead of just output the way the Mac one is). -- UUCP: Ofc: jer@peora.UUCP Home: jer@jerpc.CCUR.UUCP CCUR DNS: peora, pesnta US Mail: MS 795; CONCURRENT Computer Corp. SDC; (A Perkin-Elmer Company) 2486 Sand Lake Road, Orlando, FL 32809-7642