cv to midi???

[Christian Hofmann]

On Mon, 8 Nov 1999 11:54:54 -0000 
"Fraser, Colin J" <Colin.Fraser at scottishpower.plc.uk> wrote:

> I've never actually seen an electrical spec for a midi output stage.
> Anyone know where it might be found ?
> Since I make midi to din sync convertors that are powered from the midi
> line, I'd be interested to see whether devices they don't work with are
> still within the midi spec.

Hi Colin,
last night I had a look at the official MIDI spec.

It says:

"5 mA current loop type. Logical 0 is current ON. One output shall drive
one and only one input. [...] The receiver must require less than
5mA to turn on.
[...] 
Pin 2 of the MIDI In connector should also be left unconnected.
The grounding shield connector on the MIDI jacks should not be connected
to any circuit or chassis ground."


Then there's a schematic example:

Output: logic gate via 220R to pin 5, +5V via another 220R to pin 4.
Ground to pin 2, and to shield (whatever that's supposed to be,
considering it's inside the sendig device, not on the cable side; looks
like a shielded cable between DIN connector and the 220R's; maybe they
mean the external MIDI cable shield).
The sending logic gate is foggily specified as "IC or transistor", I've
seen 74LS04s being used for that.

Input: pin 4 via 220R to opto coupler anode, pin 5 to coupler cathode (no
resistor here), pin 2 not connected. Additionally there's a reverse
1N914 diode to protect the coupler against reverse polarity (diode anode
to coupler cathode and vice versa).
The coupler is shown as a Sharp PC900, "HP 6N138 or other can be used
with appropriate changes; other high-speed optoisolators may be
satisfactory"

Verbal schematics. I think we haven't had that before...

cu
Christian