Ryan Malloy
f2c1eb84d2
The AG3352 GNSS engine in the RYS352A ships at 115200 8N1 per the datasheet spec table. 9600 was a generic assumption that would cause the UART to read garbage and never acquire a fix.
261 lines
13 KiB
Markdown
261 lines
13 KiB
Markdown
# 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) | UBX/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. The TX line
|
||
(GPIO6) is optional — only needed if you want to send UBX configuration
|
||
commands to change update rate, constellation selection, or enable additional
|
||
NMEA sentences. The firmware uses TinyGPS++ to parse standard GGA/RMC sentences.
|
||
|
||
## 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.
|