2
4
5
1 (NC)
3 (NC)
A
B
MIDI Out/Thru Jack
(Exterior view)
An LED between pins 4 and 5 on a MIDI Out or Thru jack will flash when data passes. Fig. A: When wiring a receptacle remember that the pins are reversed. You can also connect directly to a captive MIDI cable.
Fig. B: You can wire a 220-ohm resistor in series with the LED to protect it, but for quick checks, it’s perfectly safe without one.
MATERIALS
High-intensity LED
5-pin DIN jack or MIDI cable
Insulated wire or wire wrap
Hollow toy
(Optional: 220 resistor, LED socket)
TOOLS
Soldering iron or wirewrap tool
Drill
Tapered reamer
Long-nose pliers
Wire cutters/stripper
How It Works
Only the three center pins in a MIDI Out jack are connected. Pin 2 is ground, pin 4 is +5VDC, and pin 5 is normally at +5VDC, but it drops to 0VDC when MIDI data goes out. So if you connect the anode (long leg) of an LED to pin 4 and the cathode to pin 5, the LED will flash when MIDI data goes out (see Figure B). Note that MIDI pins are numbered non-consecutively, with pin 2 in the middle, between pins 4 and 5.
You can also use this device as a visual metro-
nome. Just send it a control-change message
your instrument is generating MIDI messages for every quarter note, with a burst of messages to
both raw notes and any additional twiddling. If mark the downbeat. (If sending from a sequencer,
the detector shows that the MIDI is coming out of you may need to filter out MIDI Clock data, which
your instrument, you know you have to look else- pulses 24 times per quarter note.)
where for the reason you’re not hearing anything.
To determine if my keyboard was successfully generating data, I built this simple MIDI detector and packaged it in a small Japanese monster toy.
Besides looking cool, the toy — a Bandai Mechanikong — pulled apart easily to grant access to its insides. It also had a flat spot on the back where I David Battino ( batmosphere.com) edits the O’Reilly Digital mounted the MIDI jack. I’ve since built three more Media site ( digitalmedia.oreilly.com) and co-wrote The Art monster MIDI detectors (see previous page). of Digital Music.
See a movie of the Mechanikong MIDI detector in action at makezine.com/07/diy-monstermidi.
References:
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