# Channel3 ESP32 Port

ESP32 port of the Channel3 analog NTSC/PAL television broadcast firmware.

## Overview

This project ports the ESP8266 Channel3 firmware to ESP32, maintaining the ability to broadcast RF signals on Channel 3 (61.25 MHz) directly from a GPIO pin.

**WARNING**: RF broadcast without proper licensing may be illegal in your jurisdiction. This project is for educational purposes only.

## How It Works

The ESP32 outputs an 80 MHz bitstream via I2S DMA. Pre-computed waveform patterns create harmonics at the Channel 3 carrier frequency (61.25 MHz for luma). The GPIO pin acts as an antenna, radiating RF directly.

### Key Differences from ESP8266 Version

| Component | ESP8266 | ESP32 |
|-----------|---------|-------|
| Clock source | 160 MHz / 2 | 160 MHz / 2 (PLL_D2) |
| DMA | SLC (sdio_queue) | GDMA (lldesc_t) |
| I2S mode | Standard I2S | LCD/parallel mode |
| ISR attach | ets_isr_attach() | esp_intr_alloc() |
| Framework | ESP8266 RTOS SDK | ESP-IDF 5.x |

## Building

### Prerequisites

- ESP-IDF 5.x installed and configured
- ESP32 development board (original ESP32, not ESP32-S2/S3/C3)

### Build Commands

```bash
# Set up ESP-IDF environment
. $IDF_PATH/export.sh

# Configure the project (optional - to change settings)
idf.py menuconfig

# Build
idf.py build

# Flash
idf.py -p /dev/ttyUSB0 flash

# Monitor
idf.py -p /dev/ttyUSB0 monitor
```

## Configuration

Use `idf.py menuconfig` to access settings under "Channel3 Configuration":

- **Video Standard**: NTSC (default) or PAL
- **I2S Data Output GPIO**: GPIO pin for RF output (default: GPIO22)
- **WiFi SoftAP SSID**: Access point name (default: "Channel3")
- **WiFi SoftAP Password**: Access point password

## Hardware Setup

1. Connect a short wire (antenna) to the configured GPIO pin (default GPIO22)
2. Tune an analog TV to Channel 3
3. The ESP32 will broadcast directly - no external components needed

**Note**: The RF output is very low power. The antenna must be very close to the TV antenna for reception.

## Project Structure

```
esp32_channel3/
├── CMakeLists.txt              # Main project CMake file
├── sdkconfig.defaults          # Default SDK configuration
├── main/
│   ├── CMakeLists.txt          # Main component build file
│   ├── Kconfig.projbuild       # Configuration options
│   ├── video_broadcast.c       # I2S DMA video generation (ESP32)
│   ├── video_broadcast.h       # Video broadcast header
│   ├── 3d.c                    # Fixed-point 3D graphics engine
│   ├── 3d.h                    # 3D graphics header
│   └── user_main.c             # Application entry & demo screens
└── components/
    └── tablemaker/
        ├── CMakeLists.txt      # Component build file
        ├── broadcast_tables.c  # Premodulated RF waveforms
        ├── broadcast_tables.h  # Table definitions
        ├── CbTable.c           # NTSC/PAL line type lookup
        └── CbTable.h           # Line type definitions
```

## Technical Notes

### I2S LCD Mode

The ESP32 I2S peripheral is configured in LCD mode for parallel output. This allows continuous DMA output at high bitrates without the overhead of standard I2S framing.

### Clock Configuration

The target is 80 MHz output to match the original ESP8266 implementation:
- ESP32 PLL_D2 clock: 160 MHz
- Divider: 2
- Output: 80 MHz

### DMA Operation

DMA descriptors are configured in a circular buffer. The ISR is called on each buffer completion (EOF), filling the buffer with the next line's premodulated data.

## Known Limitations

1. **RF Quality**: ESP32 GPIO slew rate and output characteristics differ from ESP8266. RF quality may vary.
2. **Timing Sensitivity**: Video signal generation is timing-critical. Heavy system load may cause visible artifacts.
3. **Legal Restrictions**: Unlicensed RF transmission is illegal in most jurisdictions.

## Credits

Original ESP8266 Channel3: Charles Lohr (CNLohr)
ESP32 Port: Based on original architecture

## License

See LICENSE file in the parent directory.