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SB-LIVE Midi Interface |
Suggerimento : |
Attenzione
si
consiglia l'eventuale realizzazione tramite un esperto di elettronica onde
evitare spiacevoli danni alla periferica MIDI.
|
How to build a MIDI interface for a SB/SB Pro/SB16:
The SoundBlaster MIDI
port uses two pins from the 15-pin joystick port. These normally would
be redundant +5volt and ground lines. In the SoundBlaster, there are called
MIDI TXD (Transmit eXternal Data) and MIDI RXD (Receive eXternal Data).
The signals to and from
the SoundBlaster are TTL logic signals.
MIDI uses a current loop
interface, so the job of the interface box is to convert between TTL-level
signals and the MIDI current loop.
If you want to use the
MIDI interface and the SoundBlaster joystick interface simultaneously,
you can make a simple adapter by connecting one male and 2 female 15-pin
connectors to a short length of ribbon cable.
For simplicity, the schematics
show the MIDI input and output circuits seperately, but they share the
+5volt and ground lines. (Pins 8 and 5 on the SoundBlaster). The interface
uses 4-wire shielded cable to connect the computer to the interface box
and two 2-wire sheilded cables to connect the interface box to the input
and output ports on the MIDI instrument.
The MIDI input port only
can connect to one instrument, but the MIDI Out from the computer could
go to up to 5 MIDI instruments.
The schematic diagram
only shows one complete MIDI output line. You can connect up to 4 additional
MIDI outputs by adding a 220ê resistor (from the +5volt pin to pin
4 on the MIDI cable)
and a 220ê resistor
(from the buffer output to pin 5 of the MIDI plug) for each output. You
should also add a 220pf capacitor between each additional MIDI line and
ground.
Construction:
Start with using half of a dual 20-pin IC board, using the first six pins for the optocoupler and the last fourteen pins for the hex buffer. Then remove portions of some of the copper lines on the circuit board with an X-Acto knife, as is shown in the schematic in the SBMIDI2.PCX graphic file.
Cut each trace on both ends first, then remove the copper between the cuts. Now on to component installation! Be sure to use rosin-core solder and a low-wattage soldering iron. Solder the 20-pin socket to the center of the board, being careful not to bridge solder between connections. Then install the other components in the locations shown in the SBMIDI3.PCX schematic.
While looking at
the SBMIDI3.PCX
schematic, note that the ringed end
of diode D1 needs to connect to pin1 of the optocoupler.
Be sure to run hookup
wires from the ground pin on the optocoupler (Pin 4) to the ground pin
of the hex buffer (Pin 7) and between pins 11 and 12 on the hex buffer.
The remaining hookup wires are optional for additional MIDI outputs. Notice
that both a resistor and a capacitor must be connected in the same hole
for each MIDI Out. Then connect the 4-conductor sheilded cable to pins
5,8,12 and 15 of the 15-pin plug. Connect the shield to the metal case
of the plug. Connect the other end of the 4-wire cable to the corresponding
locations shown in the SBMIDI3.PCX schematic. Tie the cable sheild to the
large mounting hole in the circuit card and connect one end of each of
the two connector shielded cables to pins 4 and 5 of the MIDI plugs. Connnect
the shield in the MIDI plugs to pin 2. Mark one cable "MIDI IN" and the
other cable "MIDI OUT". Connect the other end of the cables to the
corresponding locations on the circuit card. Tie the shields to mounting
holes in the circuit card and connect all three shields together with a
hookup wire. Check the card and cables to ensure that all connections are
correct, file small notches in the cover of the aluminum box for the cables,
and wrap a piece of heavy paper around the circuit card to prevent shorting.
Your next step is to plug the 15-pin connector into the SoundBlaster and
the MIDI In and Out to the MIDI jacks on your MIDI instrument.
Testing:
A MIDI port requires software
to function. You can test the input portion of the MIDI interface with
the FM Organ program bundled with the SoundBlaster. With "MIDI Mode" selected,
MIDI Note-On messages will play sounds from the SoundBlaster card, but
only those notes valid for the musical key you have selected. For example,
if you select the key of C, only the white keys will sound. To test the
MIDI Out portion of the interface, you can use any MIDI sequencer that
supports SoundBlaster. All of Voyetra's sequencers, Cakewalk, and Trax
are examples of some that are avaliable. When you go
shopping for a sequencer,
make sure you specify that you have a SoundBlaster. The SoundBlaster/SoundBlaster
Pro MIDI interface is NOT Roland MPU-401 compatible, but the SB16's MIDI
interface is.
Parts List:
Resistors:
(¬-watt, 1%, metal
film)
R4,R5 220ê
R1 270ê
R2 1Kê
R3 4.7Kê
Capacitors:
(25 working volts or
greater)
C1,C2 220pF ceramic
Diodes:
D1 1N914 or 1N4148
Integrated Circuits:
IC1 4N35 Optocoupler
IC2 7407 Hex Buffer
IC Sockets:
(IC1) 8-pin
(IC2) 14-pin
Other Components:
1 Dual IC board, Radio
Shack part #276-159
1 15-pin male DB-style
connector, solder cup
1 Hood for 15-pin DB
connector
2 5-pin DIN plugs, 180ø
1 Aluminum project box,
approx. 3"x2"x2"
2' of 4-conductor shielded
cable
8' of 2-conductor shielded
cable
Other info:
Creative Labs, Inc. BBS: (405)742-6660 1200/2400/9600/14400 v32/v32bis
Note: Please do NOT call the Technical Support department of Creative Labs for help on this - With this file, you have just as much information as they do! If you don't want to deal with it, just _buy_ the cable - It costs $24.95 + S&H direct from Creative Labs. The sales number is (800)998-1000.
Good luck!
ATTENZIONE! E' opportuno per le informazioni necessarie fare capo ai siti internet della creative sia http: ( http://www.cle.creaf.com ) che ftp: ( ftp.cle.creaf.com ) per dati e acquisti.
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