Added circuit diagram

doc/manuals/MicroDexed-Build_Manual/MicroDexed-Build_Manual.md

@@ -422,3 +422,8 @@ First check your MIDI wiring. Are you getting signals? There should be a note or
 Is the volume high enough? Turn the volume encoder (left) so that the display shows you a higher value (maximum 100).
 
 Has the SD card been recognized? You can only hear the sound if the SD card has been recognized correctly. If not, format it again as FAT32 and copy the data or try another SD card.
+
+## Appendix
+
+### Circuit diagram
+![](images/TeensyMIDIAudio.jpg)