[sdiy] MIDI activity indicator circuit

[Arthur Harrison]

One suggestion:  Make an edge detector for each monitored point with a
resistor, capacitor, and exclusive-or gate, and follow that with a
monostable multivibrator "pulse-stretcher" that drives an LED.  There are
four exclusive or gates in a package (such as the CMOS CD4070B), and two
CMOS monostables in a package (such as the CD4538B). The monostable outputs
can probably drive high-efficiency LEDs directly at 3 to 5 milliamperes,
which would save you the LED driver, but you could also add drivers (7 in a
package for the ULN2004, and 8 in a package for the ULN2804) if you want to
deliver more current to the LEDs. You could possibly replace each monostable
with a diode, two resistors, and capacitor feeding the LED driver directly,
but the packaged monostables offer more design convenience.

-Art

----- Original Message -----
From: "Hallvard Tangeraas" <northstar2010 at yahoo.no>
To: "Synth-DIY list" <synth-diy at dropmix.xs4all.nl>
Sent: Wednesday, October 24, 2001 6:35 PM
Subject: [sdiy] MIDI activity indicator circuit


> One of my current projects is to rack-mount an Atari ST computer with
> all sorts of extra hardware goodies added, making it the ultimate MIDI
> computer (in my opinion) in a sturdy, compact 19" rack enclosure
> without having all sorts of bits and wires hanging out of it.
>
> One of the things will of course be added MIDI capabilities. I use
> Notator SL (see my signature for a mailing-list on this software which
> I run, in my signature) and with some add-on boxes from C-Lab I now
> have loads of extra MIDI in and out ports.
>
> Now, finally my question...
> I would like to add MIDI activity indicator LEDs for each IN and OUT
> port, flashing/lighting up whenever a MIDI signal goes through that
> port. Does anyone have such a circuit available?
> I know that simply connecting an LED to the MIDI pins will make it
> flash, but (a) it doesn't light up very well, and (b) I don't want to
> put any extra load on the MIDI circuitry or interfere with the signal
> in any way as I believe this is just a "quick and dirty" solution. I'm
> looking for a proper, stable solution, but hopefully nothing too
> complicated or expensive if possible.
>
>
> Hallvard
> --
> Notator/Creator SL : <http://www.notator.org>
> Atari Launchpad    : <http://launchpad.atari.org>
>
>