Ryan Malloy
7db4204d26
Replace altitude-validity heuristic with authoritative GGA quality field (SPS/DGPS/RTK) and GSA nav mode (2D/3D) via TinyGPSCustom extractors. Send $PAIR062 commands at boot to filter NMEA output to only GGA/GSA/RMC/GSV and configure PPS for fix-only pulses. GpsPayload struct gains fix_quality field (16 -> 14 bytes packed).
276 lines
14 KiB
Markdown
276 lines
14 KiB
Markdown
# BLE Bridge Wiring — ESP32-S3 + 2× MAX485
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Transparent BLE-to-RS422 bridge for the Winegard Carryout G2 satellite dish,
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with optional IMU and barometric sensors for orientation and refraction correction.
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## Parts
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**Bridge (required):**
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- ESP32-S3-DevKitC-1-N16R8
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- 2× MAX485 TTL-to-RS485 module
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- 1× SparkFun Bidirectional Logic Level Converter (BOB-12009, BSS138-based)
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- RJ-12 6P6C straight-wired cable with breakout
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- Hookup wire / jumpers
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**Sensors (optional):**
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- 1× GY-9250 (MPU-9250) — 9-axis IMU (accelerometer + gyroscope + magnetometer)
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- 1× BMP388 — barometric pressure + temperature
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- 1× RYS352A GPS module — observer location + PPS timing
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## Schematic
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```
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SparkFun Level Converter (BOB-12009)
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┌──────────────────────────────────────┐
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│ │
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ESP32 3V3 ──────────────►│ LV HV │◄── ESP32 5V
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ESP32 GND ──────────────►│ GND GND │◄── (shared)
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│ │
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ESP32 GPIO17 (TX) ──────►│ LV1 HV1 │──────► MAX485₁ DI
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ESP32 GPIO18 (RX) ◄──────│ LV2 HV2 │◄────── MAX485₂ RO
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│ │
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│ LV3 (spare) HV3 (spare) │
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│ LV4 (spare) HV4 (spare) │
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└──────────────────────────────────────┘
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MAX485 Board 1 (TX only) MAX485 Board 2 (RX only)
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┌────────────────────────┐ ┌────────────────────────┐
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│ VCC ◄── 5V │ │ VCC ◄── 5V │
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│ GND ◄── GND │ │ GND ◄── GND │
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│ │ │ │
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│ DI ◄── HV1 │ │ RO ──► HV2 │
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│ RO (unused) │ │ DI (unused) │
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│ │ │ │
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│ DE ◄── 5V ┐ locked │ │ DE ◄── GND ┐ locked │
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│ RE ◄── 5V ┘ TX mode │ │ RE ◄── GND ┘ RX mode │
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│ │ │ │
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│ A ───────────────────┼──► pin 2 │ A ◄──────────────────┼── pin 4
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│ B ───────────────────┼──► pin 3 │ B ◄──────────────────┼── pin 5
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└────────────────────────┘ └────────────────────────┘
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RJ-12 to Carryout G2
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┌───────────────────────────┐
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│ Pin 1 (White) ── GND │◄── ESP32 GND
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│ Pin 2 (Red) ── TX+/TA │◄── A₁
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│ Pin 3 (Black) ── TX-/TB │◄── B₁
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│ Pin 4 (Yellow) ── RX+/RA │──► A₂
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│ Pin 5 (Green) ── RX-/RB │──► B₂
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│ Pin 6 (Blue) ── N/C │
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└───────────────────────────┘
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```
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## Power Rails
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```
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ESP32 5V ──┬── Level Converter HV
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├── MAX485₁ VCC
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├── MAX485₁ DE + RE (tied high = TX mode)
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└── MAX485₂ VCC
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ESP32 3V3 ─── Level Converter LV
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ESP32 GND ─┬── Level Converter GND
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├── MAX485₁ GND
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├── MAX485₂ GND
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├── MAX485₂ DE + RE (tied low = RX mode)
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└── RJ-12 Pin 1
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```
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## RJ-12 Cable Notes
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Straight-wired 6P6C. Pin 1 is leftmost when looking at the jack with the clip
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facing away from you (tab down). Wire colors per the standard flat cable:
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| Pin | Color | Function | Connects to |
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|-----|--------|------------------|--------------------|
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| 1 | White | GND | Common ground |
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| 2 | Red | TX+ (TA) | MAX485₁ A |
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| 3 | Black | TX- (TB) | MAX485₁ B |
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| 4 | Yellow | RX+ (RA) | MAX485₂ A |
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| 5 | Green | RX- (RB) | MAX485₂ B |
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| 6 | Blue | N/C | — |
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If crimping your own cable, verify pin-to-color with a multimeter before
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connecting to the dish. RJ-12 crimps are easy to get reversed (pins mirror
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if the connector is flipped). A wrong connection won't damage anything
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(differential signals are current-limited) but communication won't work.
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## How It Works
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The Carryout G2 uses RS-422 full-duplex: two separate differential pairs,
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one for each direction. The MAX485 is a half-duplex RS-485 transceiver with
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a shared A/B pair and direction control pins (DE/RE). By hardwiring DE/RE,
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each board is locked into a single direction:
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- **Board 1 (TX):** DE=HIGH, RE=HIGH → driver always enabled, receiver disabled.
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ESP32 UART1 TX → level shifter → DI → differential A/B → G2 serial RX.
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- **Board 2 (RX):** DE=LOW, RE=LOW → driver disabled, receiver always enabled.
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G2 serial TX → differential A/B → RO → level shifter → ESP32 UART1 RX.
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The SparkFun level converter translates between 3.3V (ESP32) and 5V (MAX485)
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on both data lines. The two spare channels (LV3/HV3, LV4/HV4) are available
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if DE/RE ever need GPIO control for a half-duplex variant.
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## Firmware
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See `firmware/ble-bridge/` — transparent BLE Nordic UART Service (NUS) bridge.
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The firmware is the same regardless of whether the RS-422 transceiver is a
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MAX490 (single full-duplex chip) or two MAX485s (locked half-duplex pair).
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It only sees UART TX/RX on GPIO17/18.
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## Sensors — I2C Bus
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The MPU-9250 and BMP388 share a single I2C bus on GPIO8 (SDA) / GPIO9 (SCL).
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Both run at 3.3V directly from the ESP32, no level shifting needed.
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```
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I2C Bus (3.3V, 400kHz)
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─────────────────────
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ESP32 3V3 ──┬──────────────────┬─── MPU-9250 VCC
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│ └─── BMP388 VCC
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│
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├── 4.7KΩ ── SDA bus ──┬── MPU-9250 SDA
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│ └── BMP388 SDI
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│
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└── 4.7KΩ ── SCL bus ──┬── MPU-9250 SCL
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└── BMP388 SCK
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ESP32 GPIO8 (SDA) ──── SDA bus
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ESP32 GPIO9 (SCL) ──── SCL bus
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ESP32 GND ──┬── MPU-9250 GND
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└── BMP388 GND (SDO to GND = addr 0x76)
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MPU-9250 AD0 ── GND (I2C address = 0x68)
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BMP388 SDO ── GND (I2C address = 0x76)
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```
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The 4.7KΩ pull-ups are shared — one pair for the whole bus. Many breakout
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boards include onboard pull-ups already; if both the GY-9250 and BMP388
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boards have them, the combined parallel resistance (~2.3KΩ) is still fine
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for 400kHz I2C at 3.3V. Only add external pull-ups if neither board has them.
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### MPU-9250 (GY-9250) — 9-Axis IMU
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| I2C Address | 0x68 (AD0 → GND) |
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|-------------|-------------------|
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| VCC | 3-5V (onboard LDO) |
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| Interface | I2C (up to 400kHz) or SPI |
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**What it provides for satellite tracking:**
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- **Magnetometer (AK8963):** Compass heading for automatic north alignment.
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Eliminates manual alignment of dish base "BACK" marking to true north.
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Apply local magnetic declination to convert magnetic north → true north.
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- **Accelerometer:** Gravity vector → tilt angle = elevation. Independent
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verification of the dish firmware's reported EL position.
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- **Gyroscope:** Angular rate during slews. Detect oscillation, overshoot,
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and vibration for tuning the leapfrog overshoot compensation algorithm.
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**Mounting considerations:** The magnetometer is extremely sensitive to nearby
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ferrous metals and electromagnetic interference from motors. Mount on the
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fixed base plate, away from motor housings, with a known axis aligned to the
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dish's reference direction. Rigid mounting — any flex between sensor and dish
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structure introduces measurement error.
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### BMP388 — Barometric Pressure + Temperature
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| I2C Address | 0x76 (SDO → GND) |
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|-------------|-------------------|
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| VCC | 3.3V |
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| Pressure range | 300-1250 hPa |
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| Pressure resolution | ±0.01 hPa (±8 cm altitude) |
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| Temperature accuracy | ±0.5°C |
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| Interface | I2C (up to 3.4MHz) or SPI |
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**What it provides for satellite tracking:**
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- **Atmospheric refraction correction.** Radio signals bend as they pass
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through the atmosphere, especially at low elevation angles. The amount of
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bending depends on air pressure and temperature. At 15° elevation (the
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Trav'ler's minimum), refraction shifts apparent position by ~0.2°.
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Standard refraction models (Bennett, Saemundsson) take pressure and
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temperature as inputs — the BMP388 provides both in real time.
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- **Temperature monitoring.** Ambient temperature at the dish for thermal
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drift awareness and electronics health monitoring.
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**Refraction formula (simplified Bennett):**
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```
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R = 1/tan(el + 7.31/(el + 4.4)) × (P/1010) × (283/(273 + T))
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```
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Where R is refraction in arcminutes, el is apparent elevation in degrees,
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P is pressure in hPa, T is temperature in °C. At el=15°, P=1013, T=20°C:
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R ≈ 3.4 arcmin ≈ 0.057°. Small but meaningful for narrow-beam antennas.
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## GPS — RYS352A
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The RYS352A is a compact GPS module with PPS output. It connects via UART2 and
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provides observer location for satellite pass prediction and a 1Hz PPS pulse
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for precise UTC time synchronization.
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```
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ESP32 GPIO5 (UART2 RX) ◄── RYS352A TX (NMEA sentences out)
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ESP32 GPIO6 (UART2 TX) ──► RYS352A RX (config commands in, optional)
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ESP32 GPIO7 ◄── RYS352A PPS (1Hz rising edge, ~100ns jitter)
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ESP32 3V3 ──► RYS352A VCC
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ESP32 GND ──► RYS352A GND
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```
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| Module Pin | ESP32 Pin | Function |
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|------------|-----------|----------|
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| VCC | 3V3 | 3.3V power (onboard LDO on most breakouts) |
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| GND | GND | Ground |
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| TX | GPIO5 (UART2 RX) | NMEA sentence output at 115200 baud |
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| RX | GPIO6 (UART2 TX) | PAIR/NMEA config input (optional) |
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| PPS | GPIO7 | 1Hz pulse synchronized to GPS time |
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**PPS (Pulse Per Second):** The RYS352A outputs a precise 1Hz pulse on the
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rising edge, synchronized to UTC via GPS constellation. The firmware captures
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this edge via interrupt (`micros()` timestamp) for correlating satellite events
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with sub-microsecond precision relative to the GPS epoch. The module's RTC
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battery backup enables warm starts (~5s) after initial cold start fix (~30-60s).
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**UART notes:** The RYS352A defaults to 115200 baud NMEA output with `GN`
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talker ID (multi-constellation). The TX line (GPIO6) is used at boot to send
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`$PAIR` proprietary commands (Airoha AG3352 engine) that configure the GPS
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module for satellite tracking use. See `docs/RYS352x_PAIR_Command_Guide.md`
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for the full command reference.
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**Boot-time PAIR init sequence:** The firmware sends `$PAIR062` commands at
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startup to filter NMEA output — only GGA (position/quality), GSA (fix mode/DOP),
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RMC (time/date/speed), and GSV (satellite visibility, every 5th fix) are enabled.
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Redundant sentences (GLL, VTG, ZDA, GRS, GST, GNS) are disabled to reduce parser
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load and latency. A `$PAIR752` command configures PPS to pulse only on 2D/3D fix
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with 100ms pulse width. Each command waits for `$PAIR001` ACK; failures are
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logged but non-fatal — the GPS works with defaults if PAIR commands are unsupported.
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The firmware uses TinyGPS++ v1.1+ with custom field extractors (`TinyGPSCustom`)
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to read GGA quality (field 6: SPS/DGPS/RTK) and GSA nav mode (field 2: 2D/3D)
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directly from the NMEA stream, replacing the earlier heuristic that inferred
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fix type from altitude validity. Both `GN` and `GP` talker ID variants are
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registered for compatibility across constellation configurations.
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## Full GPIO Map
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| GPIO | Function | Interface | Notes |
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|------|----------|-----------|-------|
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| 5 | GPS RX | UART2 RX | ← RYS352A TX (NMEA out) |
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| 6 | GPS TX | UART2 TX | → RYS352A RX (config in) |
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| 7 | GPS PPS | GPIO interrupt | 1Hz rising edge |
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| 8 | I2C SDA | I2C | MPU-9250 + BMP388 (shared bus) |
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| 9 | I2C SCL | I2C | MPU-9250 + BMP388 (shared bus) |
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| 17 | RS-422 TX | UART1 TX | → Level shifter → MAX485₁ DI |
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| 18 | RS-422 RX | UART1 RX | ← Level shifter ← MAX485₂ RO |
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| 38 | RGB LED | WS2812 | Onboard NeoPixel (DevKitC V1.1) |
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| 43 | USB Console TX | UART0 | CH343 USB-serial (untouched) |
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| 44 | USB Console RX | UART0 | CH343 USB-serial (untouched) |
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## Loopback Test (no dish)
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Before connecting to the G2, verify the bridge by shorting MAX485₁ A to
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MAX485₂ A, and MAX485₁ B to MAX485₂ B (loop TX back into RX). Anything
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sent via BLE or USB serial should echo back.
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