By Dennis Kambury
Troubleshooting is a regular part of keeping your studio up and running, and when your MIDI gear isn't behaving like it should, it helps to have the tools to locate the problem. For years, I've carried around a simple MIDI tester that plugs into any MIDI Out port and flickers when data is being transmitted. Not long ago, a friend asked where he could find a MIDI tester of his very own, but that proved more difficult than you would think!
Despite our best efforts on the Internet, we were unable to locate a pre-made MIDI tester anywhere in the U.S., so I dug up the MIDI specs, delved into the parts box, heated up the soldering iron, and built one from scratch. (NOTE: to build the MIDI Tester you should already have some electronics-soldering experience. If you don't, study up on basic soldering techniques and cautions before you start this project.
With that caveat out of the way, here's how to make the DIY MIDI Tester:
You'll need just a few parts for this project: a short MIDI cable; a 5-volt LED (whatever color suits your fancy is fine); wire cutters; electrical tape; heat-shrink tubing; a soldering iron; and solder. You can find all of these items at your local Radio Shack.
With the wire cutters, lop the plug off one end of the MIDI cable and determine which wires go to which pins on the remaining plug. You can use an ohmmeter or just check the color of the wires. Although there are 5 pins, we'll only be using the wires connected to pins 4 and 5. See the diagram below for the standard MIDI plug pinout:
Now take a look at your LED - one lead is longer than the other, and that's the anode, or positive end. Solder the anode lead of the LED to pin 4's wire, and the short, cathode leg to pin 5's wire. That's it! To complete your tester, wrap the exposed wires with electrical tape so they don't short out against each other, and finish the whole assembly with a bit of heat-shrink tubing.
Although it's unlikely, should your tester fail to test, go back and make sure you've connected everything properly, that you're using the correct value LED, and that none of your wires are crossed.
Plug your MIDI Tester into the MIDI Out port of your keyboard (or other MIDI gear) and play. You should see bright flashes for Note On and Note Off events, CC changes, and other passing MIDI messages. MTC and Active Sensing will cause the LED to glow dimly.