🎛️ Wire Color Key

• Red → +12 V input
• Orange → +5 V regulated
• Black → Ground
• Yellow → MIDI signal lines (raw + clean)
• Blue → Logic connections (inverter inputs/outputs)
• Green → LED wiring
• White → Misc short links / regulator wiring

🧱 FULL STEP‑BY‑STEP ASSEMBLY

1. Build the 12 V → 5 V Regulator Block

Place the 78L05

Flat face toward you:
(1) IN — (2) GND — (3) OUT

Wire the input

• Red wire: 12 V → 1N4007 → 78L05 pin 1
• Black wire: 12 V ground → GND rail

Add capacitors

• 100 µF: 78L05 pin 1 → GND
• 10 µF: 78L05 pin 3 → GND
• 100 nF: 78L05 pin 3 → GND

Create rails

• Orange wire: 78L05 pin 3 → +5 V rail
• Black wire: 78L05 pin 2 → GND rail

2. Add the 5 V Power‑On LED

Place this near the regulator block.

• Green wire: +5 V rail → 1 kΩ resistor → LED anode
• LED cathode → Black wire → GND

This LED lights whenever the regulator is producing 5 V.

3. Place the ICs

• 6N138 left‑center, straddling the trench
• 74HC14 right‑center, straddling the trench

4. Power the ICs

• Orange wire: 6N138 pin 8 → +5 V
• Black wire: 6N138 pin 5 → GND
• Orange wire: 74HC14 pin 14 → +5 V
• Black wire: 74HC14 pin 7 → GND

Pull‑up

• 10 kΩ: 6N138 pin 6 → +5 V (orange)

5. Place and Wire the MIDI IN Header

Header pin mapping:

• Pin 1 = DIN pin 4
• Pin 2 = DIN pin 5
• Pin 3 = DIN pin 2 (GND)

Wire it

• Yellow wire: IN pin 1 → 220 Ω → 6N138 pin 2
• Yellow wire: IN pin 2 → 6N138 pin 3
• Black wire: IN pin 3 → GND

Protection diode

• Between 6N138 pins 2 and 3
• Stripe toward pin 2

6. Connect 6N138 Output to 74HC14 and MatrixPortal RX

• Yellow wire: 6N138 pin 6 → 74HC14 pin 1
• Blue wire: 74HC14 pin 2 → MatrixPortal RX

⭐ Important clarification:

74HC14 pin 2 is the “clean MIDI” signal.
All THRU inverter inputs will connect to this exact pin.

7. Connect ALL THRU Inverter Inputs to 74HC14 Pin 2

Use blue wires to tie each inverter input to the clean MIDI node at pin 2:

• 74HC14 pin 3 → pin 2
• 74HC14 pin 5 → pin 2
• 74HC14 pin 9 → pin 2
• 74HC14 pin 11 → pin 2

This means:

Pin 2 is the single source feeding all four THRU inverters.

8. Add THRU/OUT Activity LED

This LED shows the buffered MIDI signal feeding all THRUs and your internal OUT.

• Green wire: 74HC14 pin 2 → 1 kΩ → LED anode
• LED cathode → Black wire → GND

9. Place THRU Headers (THRU1–4)

Each header:

• Pin 1 = DIN pin 4 (from +5 V via 220 Ω)
• Pin 2 = DIN pin 5 (from inverter output via 220 Ω)
• Pin 3 = DIN pin 2 (GND)

Place them along the bottom right of the breadboard.

10. Wire THRU Outputs

THRU1 (inverter B)

• Blue wire: 74HC14 pin 4 → 220 Ω → THRU1 pin 2
• Orange wire: +5 V → 220 Ω → THRU1 pin 1
• Black wire: THRU1 pin 3 → GND

THRU2 (inverter C)

• Blue wire: 74HC14 pin 6 → 220 Ω → THRU2 pin 2
• Orange wire: +5 V → 220 Ω → THRU2 pin 1
• Black wire: THRU2 pin 3 → GND

THRU3 (inverter D)

• Blue wire: 74HC14 pin 8 → 220 Ω → THRU3 pin 2
• Orange wire: +5 V → 220 Ω → THRU3 pin 1
• Black wire: THRU3 pin 3 → GND

THRU4 (inverter E)

• Blue wire: 74HC14 pin 10 → 220 Ω → THRU4 pin 2
• Orange wire: +5 V → 220 Ω → THRU4 pin 1
• Black wire: THRU4 pin 3 → GND

11. Internal MIDI OUT (No DIN Jack)

Use the last inverter (F):

• Yellow wire: MatrixPortal TX → 74HC14 pin 13
• Blue wire: 74HC14 pin 12 → internal OUT node (your choice)

This gives you a clean, buffered logic‑level MIDI OUT.

This chapter provides the complete physical layout for assembling the MIDI Interface on a 2" × 3.5" solderable half‑breadboard perfboard (ElectroCookie style).
It includes:

• Exact placement of the 6N138, 74HC14, 78L05, NPN transistor, resistors, and capacitors
• Placement of all panel headers (MIDI IN, 4× THRU, LED, switch, DC input)
• Power‑rail usage and recommended routing strategy
• A literal, row‑and‑column‑based layout for reproducibility

Perfboard overview

You are using a 2" × 3.5" solderable half‑breadboard perfboard with:

• A center gap between rows E and F for DIP ICs
• Power rails along the left and right edges
• Rows labeled A–J (top to bottom)
• Columns numbered 1–30 (left to right)

For consistency, this manual uses:

• Row A = top edge
• Row J = bottom edge
• Column 1 = left edge
• Column 30 = right edge

ICs straddle the E/F gap.

Note -- I filed the traces off of the bottom power rails so that each of those holes is individual and can be used for the headers.

IC orientation

6N138 placement

Place the 6n138 so that:

• Pins 1-4 sit on E8–E11
• Pins 5-8 sit on F11–F8

74HC14 Placement

Place the 74HC14 so that:

• Pins 1–7 sit on E12–E18
• Pins 8–14 sit on F18–F12

This keeps it to the right of the 6N138 with clean routing to the THRU resistors.

78L05 Regulator

Place 78L04 so that:

• H26 = VIN
• H27 = GND
• H28 = +5 V

Component placement map

Below is the literal placement map for all components.

ICs

• 6N138: E8–E11 / F8–F11
• 74HC14: E12–E18 / F12–F18

Transistor

• NPN (2N3904/2N2222):
  • Collector → near F10/F11 region
  • Base → near F9 (470 Ω resistor connects here)
  • Emitter → ground rail

Recommended location: Rows G–H, Columns 9–11

Resistors

MIDI IN / Optocoupler

• 470 Ω: between 6N138 pin 6 (F10) and NPN base
• 10 kΩ: between NPN collector and +5 V rail
• 1 kΩ: LED series resistor near LED header

MIDI THRU

Place the four 220 Ω resistors in a vertical bank below the 74HC14:

• R1: G13
• R2: G14
• R3: G15
• R4: G16

Each connects from a 74HC14 output to its corresponding THRU header.

Capacitors

Regulator input side

• 0.33 µF: between H26 (VIN) and H27 (GND)
• 10 µF (16 V+): same nodes, placed nearby

Regulator output side

• 0.1 µF: between H28 (+5 V) and H27 (GND)
• 10 µF (10 V+): same nodes, placed nearby

Panel header placement

All panel headers are placed along the bottom edge (Row J) for clean wiring to the enclosure.

Left to Right:

1. MIDI IN Header (3‑pin)
   • J5–J7
2. MIDI THRU Headers (4× 3‑pin)
   • THRU1: J10–J12
   • THRU2: J14–J16
   • THRU3: J18–J20
   • THRU4: J22–J24
3. LED Header (2‑pin)
   • J26–J27
4. Power Switch Header (2‑pin)
   • J28–J29
5. DC Input Header (2‑pin)
   • J30–J31 (or nearest available)

Power rails

Use the built‑in rails:

• Left rail: Ground
• Right rail: +5 V

Connect:

• 78L05 output (H28) → +5 V rail
• 78L05 ground (H27) → ground rail
• 6N138 pin 8 (F8) → +5 V rail
• 6N138 pin 5 (F11) → ground rail
• 74HC14 pin 14 → +5 V rail
• 74HC14 pin 7 → ground rail

Recommended routing strategy

MIDI IN section

• Keep the LED‑side wiring short
• Route the 470 Ω resistor directly to the NPN base
• Keep the 10 kΩ pull‑up close to the NPN collector

THRU section

• Route each 74HC14 output straight down to its 220 Ω resistor
• Then straight to the THRU header pins
• Maintain clean, parallel lines for serviceability

Power section

• Keep regulator capacitors tight to the 78L05
• Use short, direct traces to the rails
• Avoid crossing the logic section with VIN wiring

Final checkpoints

Before soldering the wiring:

• Confirm 6N138 pin 8 is on F8 and goes to +5 V
• Confirm 6N138 pin 5 is on F11 and goes to ground
• Confirm 74HC14 pin 14 is powered and pin 7 is grounded
• Confirm all THRU resistors are 220 Ω
• Confirm the NPN emitter is grounded
• Confirm the LED resistor is 1 kΩ
• Confirm the regulator capacitors are oriented correctly

MIDI IN Header (3‑pin)

• Pin 1 → DIN Pin 4
• Pin 2 → DIN Pin 5
• Pin 3 → Ground (DIN Pin 2)

THRU Headers (4 × 3‑pin)

Each THRU jack uses:

• Pin 1 → +5 V (through 220 Ω) → DIN Pin 4
• Pin 2 → 74HC14 output (through 220 Ω) → DIN Pin 5
• Pin 3 → Ground → DIN Pin 2

Power Switch Header (2‑pin)

• Pin 1 → DC jack +V
• Pin 2 → 7805 VIN

IN LED Header (2‑pin)

• Pin 1 → LED anode (via 1 kΩ)
• Pin 2 → Ground

MatrixPortal Header (3‑pin)

• GND
• RX (from MPS6514 NPN collector)
• +5 V

Power Test

• Apply 9–15 V DC
• Verify 5 V output from the regulator
• Check for excessive heat

MIDI IN Test

• Connect a MIDI source
• Confirm IN LED activity

THRU Output Test

• Connect downstream devices
• Verify all receive identical MIDI data

MatrixPortal Test

• Connect RX and GND
• Run firmware
• Confirm MIDI events are received