Sometimes it might be nice to interface a SEGA Master System MIDI Interface (SMSM) with old school MIDI gear. This means that we need to add a 5 pin MIDI DIN plug input to our SMSM project, but how?
Well, luckily, the answer is very easy! With only a few extra components, we can take a finished SMSM interface and quickly (without spending too much cash) add a standard MIDI input.
You will need:
• An SMSM interface, finished up to step #23
• A 4n28 optocoupler
• A 100 kΩ resistor
• A 3.3 kΩ resistor
• A 1n4148 diode
• A 5-pin DIN socket or plug (depending on your MIDI gear)
http://little-scale.com/SMSM/SMSM_100/SMSM_100_Arduino_MIDI_IN.ino. Use this instead of the SMSM 100 Arduino Serial Input (as shown in the original SMSM tutorial).