How To: Add a 5-Pin DIN MIDI Input to GenMDM

Overview
GenMDM firmware 102 and above support an old style 5-pin DIN input running at 31250 baud. This is in addition to the USB MIDI input. Both can be used simultaneously.

This tutorial covers how to easily and quickly add a MIDI socket to the GenMDM hardware.

Materials Needed
In this tutorial, breadboarding will be used as this is easy, quick and doesn't require any soldering.

The following items are needed:

• GenMDM interface

• breadboard
• breadboard jumpers

• 4n28 chip
• 1n4148 diode
• 3.3kΩ resistor
• 100kΩ resistor
• 5-pin DIN socket

Step-by-Step Guide

1. Remove the Teensy board from the GenMDM interface PCB

2. Place the Teensy on the breadboard.

3. Place the 4n28 on the breadboard. In the diagram below, pins 3 and 4 are furthest away from the Teensy.

4. Connect 1n4148 diode between pins 1 and 2 of the 4n28 IC. The small stripe should be closest to pin 1.

5. Connect the 100kΩ resistor between pin 6 of the 4n28 IC and the ground bus.

6. Connect the 3.3kΩ resistor between pin5 of the 4n28 IC and the 5V bus.

7. Place the 5-pin DIN socket on the breadboard.

8. Connect the 5C VCC pin from the Teensy board to the 5V bus on the breadboard.

9. Connect the 0V ground pin from the Teensy board to the ground bus on the breadboard.

10. Connect pin 4 of the 4n28 IC to ground.

11. Connect pin 5 of the 5-pin DIN socket to pin 1 of the 4n28 IC.

12. Connect pin 4 of the 5-pin DIN socket to pin 2 of the 4n28 IC.

 13. Connect pin 5 of the 4n28 IC to digital pin 7 (the eighth pin on the left hand side) of the teensy

14. Connect the first pin of the GenMDM interface PCB to the first pin of the teensy board (i.e ground). 

15. Connect the second pin of the GenMDM interface PCB to the second pin of the teensy board.

16. Connect the third pin of the GenMDM interface PCB to the third pin of the teensy board.

17. Connect the fourth pin of the GenMDM interface PCB to the fourth pin of the teensy board.

18. Connect the fifth pin of the GenMDM interface PCB to the fifth pin of the teensy board.

19. Connect the sixth pin of the GenMDM interface PCB to the sixth pin of the teensy board.

20. Connect the seventh pin of the GenMDM interface PCB to the seventh pin of the teensy board.

21. Connect the eighth pin of the GenMDM interface PCB to the eighth pin of the teensy board.