180 lines
7.8 KiB
Plaintext
180 lines
7.8 KiB
Plaintext
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==============================
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A cheap MIDI connector box
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for the Sound Blaster card
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v1.0
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by
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Adam Mirowski
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mir@chorus.fr
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==============================
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Sound Blaster has a "built-in MIDI interface", but "all you need
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is a MIDI Connector Box (optionally available) in order to connect
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your SB to MIDI instruments or keyboards", says the add on the
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box. The list price for that gadget is as high as $79.95 and
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anyway it is not available here in France. Also, the MIDI
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interface is not compatible with the MPU-401 standard (and de
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facto norm) and is only one-way-at-a-time. So the box is not worth
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the money, except if you try to set up it by yourself. For $5 you
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can get the basic functionalities and for $10 everything which
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comes with the original one.
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Parts
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=====
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Qty Name Type Tandy ref
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---------------------------------------------------
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1 Optocoupler 4N25 276-9294
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3 Resistors 220 ohm 271-015
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1 Resistor 1 Kohm
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1 AND gate 74LS08 276-9276
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2 DIN plugs Female 5 pins 274-9110
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1 Canon DB plug Male 15 pins Not sold
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[1] Diode 1N914
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1 Veroboard (*) 5cm by 5cm
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8 Wires Not shielded
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1 Box to put all that stuff inside
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[] - didn't use it myself.
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(*) I am not sure how it is called in English. It is a piece of
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epoxide with a raster of holes spaced at 2.54mm. On one side
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there are preprinted copper tracks along each line of holes
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(in one direction only). You cut off unused portions of the
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tracks and join the other with straps, so as to get a
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primitive form of a printed circuit board. You then insert the
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electronic parts and solder them.
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Sound Blaster MIDI/Game connector REAL cabling
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==============================================
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+------------------------------------------+
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! Pin Signal !
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!------------------------------------------!
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! 1 +5V !
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! 2 X button for joystick A !
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! 3 X potentiometer for joystick A !
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! 4 Ground !
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! 5 Ground !
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! 6 Y potentiometer for joystick A !
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! 7 Y button for joystick A !
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! 8 +5V !
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! 9 +5V !
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! 10 X button for joystick B !
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! 11 X potentiometer for joystick B !
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! 12 MIDI out !
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! 13 Y potentiometer for joystick B !
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! 14 Y button for joystick B !
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! 15 MIDI in !
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+------------------------------------------+
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The interesting pins are 12, 15, 4 (or 5) and 9 (or 8 or 1).
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BTW, if your joystick Y cable assumes that pin 12 is ground (as it
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is on a normal game port), it will not work with the SB.
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Interface cabling
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=================
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The cabling is roughly the same as in the MIDI 1.0 Specification,
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except that I used a different optocoupler and "AND" gates instead
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of inverters (simply because Tandy sold the former with docs :-).
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Numbers between parentheses are pin numbers. ICs have a standard
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pin numbering scheme. Other parts have pin numbers written on
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them. For resistors, it's simply to make difference between the
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two ends.
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6 5 4
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+--!----!----!--+
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Usually ! ! IC seen from the top
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a hole --> > !
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! !
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+--!----!----!--+
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1 2 3
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"MIDI-in", "MIDI-out" design the female MIDI plugs. "Game/MIDI"
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designs the 15 pin female connector on the SB.
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FROM PIN TO PIN
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MIDI input part
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---------------
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MIDI-in (4) Resistor1 220ohm (1)
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Resistor1 220ohm (2) Optocoupler (1)
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Optocoupler (2) MIDI-in (5)
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[Optocoupler (1) Diode -]
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[Optocoupler (2) Diode +]
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Games/MIDI (9) Resistor4 1Kohm (1)
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Resistor4 1Kohm (2) Optocoupler (5)
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Games/MIDI (15) Optocoupler (5)
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Optocoupler (4) Game/MIDI (4)
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MIDI output part
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----------------
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Games/MIDI (12) AND gate (1)
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AND gate (1) AND gate (2)
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AND gate (3) Resistor2 220ohm (1)
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Resistor2 220ohm (2) MIDI-out (5)
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MIDI-out (4) Resistor3 220ohm (1)
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Resistor3 220ohm (2) Game/MIDI (9)
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Games/MIDI (9) AND gate (14)
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Games/MIDI (4) AND gate (7)
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Final remarks
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=============
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When using a "veroboard", don't forget to cut tracks under the IC
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and the optocoupler, or they will be short-circuited.
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You will probably also want to setup two MIDI cords, to attach the
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interface to an instrument. To stay under $5, you could use male
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plugs instead of female ones for the interface and plug them
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directly into the instrument.
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When preparing the cords, be careful about not swapping the wires.
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The pin 4 from one plug must be wired to pin 4 from the other end,
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and the pin 5 must be attached to pin 5. None of the other pins
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must be wired, nor the overall cable shielded. There is no ground
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in MIDI cords.
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If you want more outputs, you have to slightly extend the MIDI
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output part. I would rather have only one AND gate input attached
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to the SB MIDI-out pin and only one MIDI-out plug per AND gate
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output. If Creative Labs offer 5 MIDI outs in the original
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Connector Box, it is probably because they use simple inverters
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(or buffers) and there are 6 per IC. As I previously said, I
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bought AND gates only because they had data sheets attached,
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whereas inverters/buffers had not...
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Direct your remarks to mir@chorus.fr, or to
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M. Adam Mirowski
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Chorus systemes
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6, avenue Gustave Eiffel
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F-78182 Saint-Quentin-en-Yvelines CEDEX
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FRANCE
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My phone number is +33 (1) 30-64-82-00
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I obviously won't take any responsibility for the damages you
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could do to your Sound Blaster or to your MIDI equipment while
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using this interface.
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Downloaded From P-80 International Information Systems 304-744-2253
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