Ryan Malloy
f218cd468b
RYS352A GPS on UART2 (GPIO5/6) with PPS interrupt (GPIO7), MPU-9250 IMU and BMP388 barometer on shared I2C bus (GPIO8/9). Sensor data exposed via dedicated BLE service with binary notify characteristics alongside the existing NUS serial bridge. Sensors degrade gracefully if not wired.
261 lines
13 KiB
Markdown
261 lines
13 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 9600 baud |
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| RX | GPIO6 (UART2 TX) | UBX/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 9600 baud NMEA output. The TX line
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(GPIO6) is optional — only needed if you want to send UBX configuration
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commands to change update rate, constellation selection, or enable additional
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NMEA sentences. The firmware uses TinyGPS++ to parse standard GGA/RMC sentences.
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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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