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