Provides a stable 5 V supply from a 9–15 V DC input source.

Regulator Pinout (front view)

• Pin 1: VIN
• Pin 2: GND
• Pin 3: VOUT (5 V)

Input Side Components

• DC jack → Power switch → 7805 Pin 1
• 0.33 µF ceramic capacitor from Pin 1 to Pin 2
• 10 µF electrolytic capacitor from Pin 1 to Pin 2

Output Side Components

• 7805 Pin 3 → +5 V rail
• 0.1 µF ceramic capacitor from Pin 3 to Pin 2
• 10 µF electrolytic capacitor from Pin 3 to Pin 2

Thermal Notes

At 15 V input, the regulator may dissipate up to 0.4 W depending on load. Mount the 7805 with airflow clearance or attach a small heatsink if desired.

Converts the MIDI current loop into a logic‑level signal while maintaining galvanic isolation.

DIN input wiring

• DIN Pin 4 → 220 Ω resistor → 6N138 Pin 2
• DIN Pin 5 → 6N138 Pin 3
• DIN Pin 2 → Ground

This forms the standard MIDI current loop into the optocoupler.

Optocoupler power and bias

• 6N138 Pin 5 → Ground
• 6N138 Pin 8 → +5 V
• 6N138 Pin 7 (VB) → Leave unconnected for MIDI applications
  • (VB is used for CTR tuning in other applications, but not needed here)

Optocoupler output stage

• 6N138 Pin 6 (VO) → 10 kΩ pull‑up resistor → +5 V
• 6N138 Pin 6 (VO) → 470 Ω resistor → MPS6514 NPN Base
• MPS6514 NPN Emitter → Ground
• MPS6514 NPN Collector → +5 V through 10 kΩ pull‑up

This transistor stage strengthens the optocoupler output and ensures clean edges.

Logic output to 74HC14

• MPS6514 NPN Collector → 74HC14 Pin 1
• 74HC14 Pin 2 = cleaned, conditioned MIDI logic signal.

IN Activity LED

• MPS6514 NPN Collector → 1 kΩ resistor → LED anode
• LED cathode → Ground

The LED flashes on incoming MIDI activity.

Generates four identical, low‑latency copies of the cleaned MIDI signal.

Signal Conditioning

• 74HC14 Pin 1 → Pin 2 (first inverter)
• Pin 2 fans out to:
  • Pin 3
  • Pin 5
  • Pin 8
  • Pin 10

Output Pins

• THRU 1: Pin 4
• THRU 2: Pin 6
• THRU 3: Pin 9
• THRU 4: Pin 11

Each output passes through a 220 Ω resistor before reaching the panel‑mounted THRU jack.