MIDI (cable) tester: A tester for MIDI connection is a real asset for many constructors. The one presented here is kept fairly simple as shown in Fig. 1.
The LED shows whether MIDI data are present where the tester is connected. Since these data consist of very short pulses, the LED must be a high-efficiency type.
To test both ends of a cable, the tester must be built in duplicate: one terminated into a socket and the other into a plug. A possible design is shown in Fig. 2.
The connectors should preferably be metal DIN types. The LED can be housed in the rubber support sleeve as shown in Fig. 3. The connecting wires to the LED must, of course, be well insulated.
This tests USB MIDI in host mode.
- Set the Android device’s volume to around halfway.
- Plug in the USB keyboard using the OTG adapter.
- Start either the SynthExample or the MidiScope apps.
- From the menu select the USB keyboard. It will display the brand.
- On the keyboard, play some notes. You should hear notes being played on the phone if you run SynthExample. If you used MidiScope, you should have seen the NoteOn and NoteOff notifications on your screen.
- Unplug the keyboard. The Sender for Synth menu should display – – – – –.
- Exit the application by pressing the Back button.
Why do MIDI cables use all 5 pins?
While the connectors have five pins, only three of them are used. If you want to wire your own MIDI cable, you’ll need two male, 5-pin DIN connectors and a length of shielded, twisted-pair (STP) cable.
MIDI is electronic data transmitted over an unbalanced cable, so cable length and quality have the same implications as unbalanced audio lines: shorter and higher quality are better. 20 feet is a very safe and conservative limit for MIDI cable length. Runs of 50 feet or more are possible with high-quality cable.
