# BLE Bridge Wiring — ESP32-S3 + 2× MAX485

Transparent BLE-to-RS422 bridge for the Winegard Carryout G2 satellite dish,
with optional IMU and barometric sensors for orientation and refraction correction.

## Parts

**Bridge (required):**
- ESP32-S3-DevKitC-1-N16R8
- 2× MAX485 TTL-to-RS485 module
- 1× SparkFun Bidirectional Logic Level Converter (BOB-12009, BSS138-based)
- RJ-12 6P6C straight-wired cable with breakout
- Hookup wire / jumpers

**Sensors (optional):**
- 1× GY-9250 (MPU-9250) — 9-axis IMU (accelerometer + gyroscope + magnetometer)
- 1× BMP388 — barometric pressure + temperature
- 1× RYS352A GPS module — observer location + PPS timing

## Schematic

```
                          SparkFun Level Converter (BOB-12009)
                         ┌──────────────────────────────────────┐
                         │                                      │
ESP32 3V3 ──────────────►│ LV                            HV │◄── ESP32 5V
ESP32 GND ──────────────►│ GND                          GND │◄── (shared)
                         │                                      │
ESP32 GPIO17 (TX) ──────►│ LV1                          HV1 │──────► MAX485₁ DI
ESP32 GPIO18 (RX) ◄──────│ LV2                          HV2 │◄────── MAX485₂ RO
                         │                                      │
                         │  LV3  (spare)          HV3  (spare)  │
                         │  LV4  (spare)          HV4  (spare)  │
                         └──────────────────────────────────────┘


    MAX485 Board 1 (TX only)              MAX485 Board 2 (RX only)
    ┌────────────────────────┐            ┌────────────────────────┐
    │  VCC ◄── 5V            │            │  VCC ◄── 5V            │
    │  GND ◄── GND           │            │  GND ◄── GND           │
    │                        │            │                        │
    │  DI  ◄── HV1           │            │  RO  ──► HV2           │
    │  RO     (unused)       │            │  DI     (unused)       │
    │                        │            │                        │
    │  DE  ◄── 5V ┐ locked   │            │  DE  ◄── GND ┐ locked  │
    │  RE  ◄── 5V ┘ TX mode  │            │  RE  ◄── GND ┘ RX mode │
    │                        │            │                        │
    │  A  ───────────────────┼──► pin 2   │  A  ◄──────────────────┼── pin 4
    │  B  ───────────────────┼──► pin 3   │  B  ◄──────────────────┼── pin 5
    └────────────────────────┘            └────────────────────────┘

                        RJ-12 to Carryout G2
                    ┌───────────────────────────┐
                    │  Pin 1 (White)  ── GND     │◄── ESP32 GND
                    │  Pin 2 (Red)    ── TX+/TA  │◄── A₁
                    │  Pin 3 (Black)  ── TX-/TB  │◄── B₁
                    │  Pin 4 (Yellow) ── RX+/RA  │──► A₂
                    │  Pin 5 (Green)  ── RX-/RB  │──► B₂
                    │  Pin 6 (Blue)   ── N/C     │
                    └───────────────────────────┘
```

## Power Rails

```
ESP32 5V ──┬── Level Converter HV
           ├── MAX485₁ VCC
           ├── MAX485₁ DE + RE (tied high = TX mode)
           └── MAX485₂ VCC

ESP32 3V3 ─── Level Converter LV

ESP32 GND ─┬── Level Converter GND
           ├── MAX485₁ GND
           ├── MAX485₂ GND
           ├── MAX485₂ DE + RE (tied low = RX mode)
           └── RJ-12 Pin 1
```

## RJ-12 Cable Notes

Straight-wired 6P6C. Pin 1 is leftmost when looking at the jack with the clip
facing away from you (tab down). Wire colors per the standard flat cable:

| Pin | Color  | Function         | Connects to       |
|-----|--------|------------------|--------------------|
| 1   | White  | GND              | Common ground      |
| 2   | Red    | TX+ (TA)         | MAX485₁ A          |
| 3   | Black  | TX- (TB)         | MAX485₁ B          |
| 4   | Yellow | RX+ (RA)         | MAX485₂ A          |
| 5   | Green  | RX- (RB)         | MAX485₂ B          |
| 6   | Blue   | N/C              | —                  |

If crimping your own cable, verify pin-to-color with a multimeter before
connecting to the dish. RJ-12 crimps are easy to get reversed (pins mirror
if the connector is flipped). A wrong connection won't damage anything
(differential signals are current-limited) but communication won't work.

## How It Works

The Carryout G2 uses RS-422 full-duplex: two separate differential pairs,
one for each direction. The MAX485 is a half-duplex RS-485 transceiver with
a shared A/B pair and direction control pins (DE/RE). By hardwiring DE/RE,
each board is locked into a single direction:

- **Board 1 (TX):** DE=HIGH, RE=HIGH → driver always enabled, receiver disabled.
  ESP32 UART1 TX → level shifter → DI → differential A/B → G2 serial RX.

- **Board 2 (RX):** DE=LOW, RE=LOW → driver disabled, receiver always enabled.
  G2 serial TX → differential A/B → RO → level shifter → ESP32 UART1 RX.

The SparkFun level converter translates between 3.3V (ESP32) and 5V (MAX485)
on both data lines. The two spare channels (LV3/HV3, LV4/HV4) are available
if DE/RE ever need GPIO control for a half-duplex variant.

## Firmware

See `firmware/ble-bridge/` — transparent BLE Nordic UART Service (NUS) bridge.
The firmware is the same regardless of whether the RS-422 transceiver is a
MAX490 (single full-duplex chip) or two MAX485s (locked half-duplex pair).
It only sees UART TX/RX on GPIO17/18.

## Sensors — I2C Bus

The MPU-9250 and BMP388 share a single I2C bus on GPIO8 (SDA) / GPIO9 (SCL).
Both run at 3.3V directly from the ESP32, no level shifting needed.

```
                    I2C Bus (3.3V, 400kHz)
                    ─────────────────────

ESP32 3V3 ──┬──────────────────┬─── MPU-9250 VCC
             │                  └─── BMP388 VCC
             │
             ├── 4.7KΩ ── SDA bus ──┬── MPU-9250 SDA
             │                      └── BMP388 SDI
             │
             └── 4.7KΩ ── SCL bus ──┬── MPU-9250 SCL
                                    └── BMP388 SCK

ESP32 GPIO8  (SDA) ──── SDA bus
ESP32 GPIO9  (SCL) ──── SCL bus

ESP32 GND ──┬── MPU-9250 GND
             └── BMP388 GND (SDO to GND = addr 0x76)

MPU-9250 AD0 ── GND  (I2C address = 0x68)
BMP388   SDO ── GND  (I2C address = 0x76)
```

The 4.7KΩ pull-ups are shared — one pair for the whole bus. Many breakout
boards include onboard pull-ups already; if both the GY-9250 and BMP388
boards have them, the combined parallel resistance (~2.3KΩ) is still fine
for 400kHz I2C at 3.3V. Only add external pull-ups if neither board has them.

### MPU-9250 (GY-9250) — 9-Axis IMU

| I2C Address | 0x68 (AD0 → GND) |
|-------------|-------------------|
| VCC | 3-5V (onboard LDO) |
| Interface | I2C (up to 400kHz) or SPI |

**What it provides for satellite tracking:**

- **Magnetometer (AK8963):** Compass heading for automatic north alignment.
  Eliminates manual alignment of dish base "BACK" marking to true north.
  Apply local magnetic declination to convert magnetic north → true north.
- **Accelerometer:** Gravity vector → tilt angle = elevation. Independent
  verification of the dish firmware's reported EL position.
- **Gyroscope:** Angular rate during slews. Detect oscillation, overshoot,
  and vibration for tuning the leapfrog overshoot compensation algorithm.

**Mounting considerations:** The magnetometer is extremely sensitive to nearby
ferrous metals and electromagnetic interference from motors. Mount on the
fixed base plate, away from motor housings, with a known axis aligned to the
dish's reference direction. Rigid mounting — any flex between sensor and dish
structure introduces measurement error.

### BMP388 — Barometric Pressure + Temperature

| I2C Address | 0x76 (SDO → GND) |
|-------------|-------------------|
| VCC | 3.3V |
| Pressure range | 300-1250 hPa |
| Pressure resolution | ±0.01 hPa (±8 cm altitude) |
| Temperature accuracy | ±0.5°C |
| Interface | I2C (up to 3.4MHz) or SPI |

**What it provides for satellite tracking:**

- **Atmospheric refraction correction.** Radio signals bend as they pass
  through the atmosphere, especially at low elevation angles. The amount of
  bending depends on air pressure and temperature. At 15° elevation (the
  Trav'ler's minimum), refraction shifts apparent position by ~0.2°.
  Standard refraction models (Bennett, Saemundsson) take pressure and
  temperature as inputs — the BMP388 provides both in real time.
- **Temperature monitoring.** Ambient temperature at the dish for thermal
  drift awareness and electronics health monitoring.

**Refraction formula (simplified Bennett):**
```
R = 1/tan(el + 7.31/(el + 4.4)) × (P/1010) × (283/(273 + T))
```
Where R is refraction in arcminutes, el is apparent elevation in degrees,
P is pressure in hPa, T is temperature in °C. At el=15°, P=1013, T=20°C:
R ≈ 3.4 arcmin ≈ 0.057°. Small but meaningful for narrow-beam antennas.

## GPS — RYS352A

The RYS352A is a compact GPS module with PPS output. It connects via UART2 and
provides observer location for satellite pass prediction and a 1Hz PPS pulse
for precise UTC time synchronization.

```
ESP32 GPIO5 (UART2 RX) ◄── RYS352A TX  (NMEA sentences out)
ESP32 GPIO6 (UART2 TX) ──► RYS352A RX  (config commands in, optional)
ESP32 GPIO7             ◄── RYS352A PPS (1Hz rising edge, ~100ns jitter)
ESP32 3V3               ──► RYS352A VCC
ESP32 GND               ──► RYS352A GND
```

| Module Pin | ESP32 Pin | Function |
|------------|-----------|----------|
| VCC | 3V3 | 3.3V power (onboard LDO on most breakouts) |
| GND | GND | Ground |
| TX | GPIO5 (UART2 RX) | NMEA sentence output at 115200 baud |
| RX | GPIO6 (UART2 TX) | PAIR/NMEA config input (optional) |
| PPS | GPIO7 | 1Hz pulse synchronized to GPS time |

**PPS (Pulse Per Second):** The RYS352A outputs a precise 1Hz pulse on the
rising edge, synchronized to UTC via GPS constellation. The firmware captures
this edge via interrupt (`micros()` timestamp) for correlating satellite events
with sub-microsecond precision relative to the GPS epoch. The module's RTC
battery backup enables warm starts (~5s) after initial cold start fix (~30-60s).

**UART notes:** The RYS352A defaults to 115200 baud NMEA output with `GN`
talker ID (multi-constellation). The TX line (GPIO6) is used at boot to send
`$PAIR` proprietary commands (Airoha AG3352 engine) that configure the GPS
module for satellite tracking use. See `docs/RYS352x_PAIR_Command_Guide.md`
for the full command reference.

**Boot-time PAIR init sequence:** The firmware sends `$PAIR062` commands at
startup to filter NMEA output — only GGA (position/quality), GSA (fix mode/DOP),
RMC (time/date/speed), and GSV (satellite visibility, every 5th fix) are enabled.
Redundant sentences (GLL, VTG, ZDA, GRS, GST, GNS) are disabled to reduce parser
load and latency. A `$PAIR752` command configures PPS to pulse only on 2D/3D fix
with 100ms pulse width. Each command waits for `$PAIR001` ACK; failures are
logged but non-fatal — the GPS works with defaults if PAIR commands are unsupported.

The firmware uses TinyGPS++ v1.1+ with custom field extractors (`TinyGPSCustom`)
to read GGA quality (field 6: SPS/DGPS/RTK) and GSA nav mode (field 2: 2D/3D)
directly from the NMEA stream, replacing the earlier heuristic that inferred
fix type from altitude validity. Both `GN` and `GP` talker ID variants are
registered for compatibility across constellation configurations.

## Full GPIO Map

| GPIO | Function | Interface | Notes |
|------|----------|-----------|-------|
| 5 | GPS RX | UART2 RX | ← RYS352A TX (NMEA out) |
| 6 | GPS TX | UART2 TX | → RYS352A RX (config in) |
| 7 | GPS PPS | GPIO interrupt | 1Hz rising edge |
| 8 | I2C SDA | I2C | MPU-9250 + BMP388 (shared bus) |
| 9 | I2C SCL | I2C | MPU-9250 + BMP388 (shared bus) |
| 17 | RS-422 TX | UART1 TX | → Level shifter → MAX485₁ DI |
| 18 | RS-422 RX | UART1 RX | ← Level shifter ← MAX485₂ RO |
| 38 | RGB LED | WS2812 | Onboard NeoPixel (DevKitC V1.1) |
| 43 | USB Console TX | UART0 | CH343 USB-serial (untouched) |
| 44 | USB Console RX | UART0 | CH343 USB-serial (untouched) |

## Loopback Test (no dish)

Before connecting to the G2, verify the bridge by shorting MAX485₁ A to
MAX485₂ A, and MAX485₁ B to MAX485₂ B (loop TX back into RX). Anything
sent via BLE or USB serial should echo back.