# PMIM-1 Assembly Guide
## Portable Marine Instrument Multiplexer

The PMIM-1 is a self-contained sensor box that attaches to a stanchion or companionway and streams NMEA 0183 sentences to the Nav app over Wi-Fi UDP broadcast. It provides GPS, AIS, heading, attitude (heel/pitch), and barometric pressure/temperature.

---

## Parts list

| Part | Notes | Est. Cost |
|---|---|---|
| ESP32 DevKit V1 (30-pin) | Must be 30-pin, not 38-pin | $9 |
| dAISy Mini (UART variant) | TTL UART version, not USB | $85 |
| BN-880 module | Circular PCB ~28mm, integrated ceramic patch antenna | $24 |
| GY-521 (MPU-6050) | Small blue board ~21×16mm | $8 |
| BMP280 breakout | Verify BMP280, not BMP180 | $3 |
| IP67 enclosure, white body / clear lid | ~120×80×40mm interior | $15 |
| Anker PowerCore 10000mAh | No auto-shutoff at light load | $20 |
| IP67 SMA female bulkhead | Panel-mount style with O-ring | $5 |
| BNC-F to PL-259 adapter | For VHF antenna connection | $7 |
| IPEX (U.FL) to SMA pigtail, ~100mm | Connects dAISy to bulkhead | incl. |
| GoPro adhesive base + handlebar clamp | Standard Hero mount ecosystem | $15 |
| 28 AWG silicone wire | ~1m each: red, black, yellow, green, blue, white, orange | $5 |
| M2×6 standoffs + screws | 8× for ESP32 and dAISy | $2 |
| Perfboard, ~50×70mm | Single-sided, wiring substrate | $1 |
| PG7 cable gland | Sized for USB-C cable OD (~4–5mm) | $2 |
| 4.7kΩ resistors | 2× for I2C pull-ups if BMP280 board lacks them | — |
| 47Ω 0.5W resistor | Power bank keepalive load (optional, see notes) | — |
| Gore-Tex speaker mesh tape | Breathable waterproof vent cover | $3 |
| Silicone O-ring grease | Thin smear on lid O-ring at close-up | — |
| **Total** | | **~$204** |

---

## Tools

- Soldering iron, fine tip, 320–350°C
- Solder, 0.5mm rosin-core, and flux pen
- Multimeter (continuity + DC voltage)
- Step drill or 15.5mm bit (SMA bulkhead hole)
- 4mm drill bit (BMP280 vent)
- PG7 cable gland hole size per gland datasheet (~12mm)
- Rotary tool or hand drill
- Hot glue gun (strain relief)
- Tweezers and helping hands

---

## Enclosure orientation

Orient the enclosure so the **clear lid faces up toward the sky**. This gives the BN-880's ceramic patch antenna a direct sky view. The GoPro mount adheres to the solid bottom face.

```
      Clear lid (faces sky)
      ┌─────────────────────────┐
      │   GPS antenna view      │
      └─────────────────────────┘
      Front face (toward bow preferred)
      ┌──────────┐
      │  [SMA]   │  ← AIS antenna exits here
      └──────────┘
      Back face
      ┌──────────────────────────┐
      │  [4mm vent, Gore-Tex]    │  ← BMP280 pressure equalization
      └──────────────────────────┘
      Bottom face (GoPro mount)
      ┌──────────────────────────┐
      │  [PG7 cable gland]       │  ← USB-C power from power bank
      └──────────────────────────┘
```

---

## Step 1 — Drill the enclosure

1. **SMA bulkhead hole:** Center on the front face, ~15mm from one edge. Step-drill to 15.5mm. Install the SMA bulkhead connector with O-ring and nut — finger-tight plus ¼ turn.

2. **BMP280 vent:** 4mm hole on the back face, as high as possible to avoid splash. Leave uncovered until components are mounted (Step 5).

3. **Power cable gland:** Bottom face. Drill to PG7 spec (~12mm). Thread the USB-C cable through before soldering its end — you can't pull a USB-C plug through a gland.

---

## Step 2 — Perfboard layout

Cut perfboard to fit the enclosure floor with ~5mm clearance each side. Lay out components before soldering anything:

```
┌────────────────────────────────────────────┐
│                                            │
│  [BN-880]              [ESP32 DevKit V1]   │
│  compass far corner    ┌────────────────┐  │
│  ≥35mm from ESP32      │                │  │
│   ○ (28mm circle)      │  30-pin        │  │
│                        │  DevKit        │  │
│  [BMP280]              │                │  │
│  near back vent        └────────────────┘  │
│                                            │
│  [GY-521]      [dAISy Mini]                │
│  center        right side, near SMA wall   │
│                                            │
└────────────────────────────────────────────┘
```

> **Critical:** Keep BN-880 (HMC5883L compass) at least 35mm from the ESP32. The 2.4 GHz Wi-Fi radio causes magnetic interference at close range.

Mount ESP32 and dAISy on M2×6 standoffs. Mount BN-880, GY-521, and BMP280 with double-sided foam tape, BN-880 ceramic antenna facing up toward the clear lid.

---

## Step 3 — Power wiring

```
Power bank → USB-C cable → PG7 cable gland
    → ESP32 VIN (5V)    [red wire]
    → ESP32 GND         [black wire]

ESP32 3.3V pin → 3.3V bus rail along perfboard edge
ESP32 GND      → GND bus rail

3.3V rail → dAISy VCC, BN-880 VCC, GY-521 VCC, BMP280 VCC
GND rail  → all module GNDs
```

> **Before powering:** Measure 3.3V rail to GND resistance cold (power off). Should be several kΩ. A short here will kill the ESP32's onboard regulator.

**Power bank keepalive:** If the power bank cuts out at light load, solder a 47Ω 0.5W resistor between the 5V and GND rails on the perfboard. This draws ~100mA continuously and keeps the bank alive. Try without it first — Anker PowerCore units usually don't need it.

---

## Step 4 — UART wiring

| Signal | ESP32 pin | Module pin | Wire color |
|---|---|---|---|
| UART1 RX | GPIO16 | dAISy TX | Yellow |
| UART1 TX | GPIO17 | dAISy RX | Orange |
| UART2 RX | GPIO4 | BN-880 TX | Green |
| UART2 TX | GPIO2 | BN-880 RX | White |

> dAISy RX and BN-880 RX are only needed for sending config commands. Leave them unconnected for basic operation if you want to keep it simple.

**Baud rates:**
- dAISy Mini UART: 38400 8N1
- BN-880 GPS: 9600 8N1 (default)

---

## Step 5 — I2C bus wiring

Single shared bus to all three sensors:

| Signal | ESP32 pin | Wire color |
|---|---|---|
| SDA | GPIO21 | Blue |
| SCL | GPIO22 | Purple |

Daisy-chain both SDA and SCL to each sensor: GY-521 → BN-880 → BMP280.

**Pull-up resistors:** GY-521 and BN-880 breakouts have 4.7kΩ pull-ups onboard. Check your BMP280 board — if it lacks them, add 4.7kΩ from SDA→3.3V and SCL→3.3V on the perfboard.

**I2C addresses:**

| Device | Address | How to set |
|---|---|---|
| MPU-6050 (GY-521) | 0x68 | Leave AD0 floating or tie to GND |
| HMC5883L (BN-880) | 0x1E | Fixed |
| BMP280 | 0x76 | SDO pulled LOW (0x77 if HIGH) |

---

## Step 6 — RF chain

```
dAISy Mini IPEX/U.FL port
    → IPEX-to-SMA pigtail (route flat inside enclosure)
    → SMA bulkhead (in enclosure wall, O-ring sealed)
    → [outside] BNC-F to PL-259 adapter
    → VHF antenna coax
```

Keep the IPEX pigtail as short as possible and route it away from I2C and UART wires. Seat the IPEX connector firmly — it should click.

---

## Step 7 — Calibration button

Add a normally-open tactile button for IMU zero-offset calibration:

- One terminal → GPIO0
- Other terminal → GND
- 10kΩ pull-up from GPIO0 → 3.3V (or use ESP32 internal pull-up in firmware)

For field access without opening the box, thread an IP67 panel-mount push-button through the enclosure wall. Otherwise, accept that calibration requires opening the lid — acceptable for initial dock setup.

---

## Step 8 — BMP280 pressure vent

Cut a 15mm circle of Gore-Tex speaker mesh tape. Apply it over the 4mm vent hole from the **inside** of the enclosure, pressing firmly around all edges. This lets atmospheric pressure equalize for accurate barometer readings while blocking water.

Position the BMP280 within 20mm of this hole with its sensor port facing toward it.

---

## Step 9 — Pre-close checklist

Run through this before sealing the enclosure:

- [ ] Continuity: all GND connections ring out to common ground
- [ ] No shorts: 3.3V rail to GND ≥ 5kΩ cold
- [ ] IPEX connector fully seated (it clicks)
- [ ] SMA bulkhead O-ring seated, nut snug
- [ ] PG7 cable gland compression ring tight around USB-C cable
- [ ] BN-880 ceramic antenna facing up toward clear lid
- [ ] All wires lie flat — none above the tallest component
- [ ] I2C scan (with firmware running) shows 0x1E, 0x68, 0x76
- [ ] NMEA sentences confirmed arriving on phone before sealing

---

## Step 10 — Seal and mount

1. Confirm lid O-ring is clean and seated in its groove. Apply a thin smear of silicone grease.
2. Close lid. Tighten all screws evenly in a cross-pattern.
3. **IP test:** Hold under running tap water for 10 seconds. Dry, open, check for moisture. Do this before attaching the GoPro mount.
4. Attach GoPro adhesive base to the bottom face (or use the handlebar clamp on a stanchion).

**Companionway:** Peel adhesive, press to clean dry surface, weight for 24h cure.  
**Stanchion:** Handlebar clamp around 25mm tube. Use a rubber shim if your stanchion diameter differs. Orient clear lid skyward and inboard for best GPS view.

---

## First power-on

1. Leave box open for initial test.
2. Connect power bank. ESP32 LED should illuminate.
3. On your phone, join the PMIM-1 Wi-Fi AP (SSID set in firmware).
4. Open Nav app → enable NMEA Instruments in hardware settings.
5. Confirm data: GPS fix within ~60s cold start; AIS targets if vessels nearby; attitude immediately; baro after a few seconds.
6. Tilt the box ~15° and confirm the inclinometer in the app responds.
7. Close box, re-test over Wi-Fi.

---

## Troubleshooting

| Symptom | Likely cause | Fix |
|---|---|---|
| Power bank cuts out after ~30s | Auto-shutoff at light load | Add 47Ω keepalive resistor |
| Compass heading drifts or spins | BN-880 too close to ESP32 | Increase separation, add mu-metal shim |
| No AIS targets (even near traffic) | IPEX not seated / bad antenna connection | Re-seat IPEX, check SMA continuity |
| dAISy takes ~30s to start | Normal warm-up | Wait — not a fault |
| GPS cold start >5 min | Poor sky view | Orient clear lid more skyward |
| 0x76 missing from I2C scan | BMP280 SDO high (→ 0x77) or bad connection | Check SDO pin, rescan at 0x77 |
| Baro reads but lags weather changes | Vent hole blocked or Gore-Tex not breathable | Check mesh tape seal |

---

## Pin summary

```
ESP32 DevKit V1 — complete pin assignment

GPIO1  → UART0 TX (debug/flash — do not use for peripherals)
GPIO3  → UART0 RX (debug/flash — do not use for peripherals)
GPIO2  → UART2 TX → BN-880 RX
GPIO4  → UART2 RX → BN-880 TX
GPIO16 → UART1 RX → dAISy TX
GPIO17 → UART1 TX → dAISy RX
GPIO21 → I2C SDA  → MPU-6050, HMC5883L, BMP280
GPIO22 → I2C SCL  → MPU-6050, HMC5883L, BMP280
GPIO0  → Calibration button (pull-up, active LOW)
VIN    → 5V from power bank
3.3V   → 3.3V supply rail
GND    → Common ground
```