PCB Interface

NHP_Synth: ESP32 Dual DDS Synthesizer

This project implements a dual-channel Direct Digital Synthesis (DDS) signal generator on the ESP32 platform. It features:

• Two independent sine wave outputs (via DACs on GPIO25 and GPIO26)
• Precise square wave output (GPIO18) synchronized to DDS phase
• UART command interface for real-time control
• Phase, frequency, and amplitude control for each channel
• Odd harmonic mixing with amplitude and phase control per channel (total 8 simultaneous harmonics across both channels)
• External sync input (GPIO19, rising edge)
• High-resolution timer for accurate waveform generation

Features

• Frequency Range: 20 Hz to 8 kHz (configurable)
• Amplitude Ramping: Smooth amplitude changes to prevent clicks
• Phase Control: Set phase offset for each channel
• Harmonic Mixing: Add odd harmonics (3rd, 5th, 7th, etc) to either channel, with amplitude and phase control. Up to a total of 8 harmonics can be active across both channels at once.
• UART Commands:
  • wf[a|b]<freq>: Set channel A or B frequency (Hz)
  • wp[a|b]<deg>: Set channel A or B phase (degrees, -180 to +180)
  • wa[a|b]<ampl>: Set channel A or B amplitude (0-100)
  • wh[a|b]<order>,<pct>[,<phase>]: Mix odd harmonic to channel A or B (e.g. wha3,10 for 10% 3rd harmonic, or wha7,20,-90 for 20% 7th harmonic at -90° phase)
  • whcl[a|b]: Clear all harmonics for channel A or B
  • help: Show help message

Hardware Connections

• DAC Channel A: GPIO25
• DAC Channel B: GPIO26
• Square Wave Output: GPIO18
• Sync Input: GPIO19 (rising edge, with pulldown)

Project Structure

NHP_Synth/
├── firmware/           # ESP32 firmware (ESP-IDF project)
│   ├── main/          # Main application source
│   ├── .devcontainer/ # ESP-IDF development container
│   └── .vscode/       # ESP32-specific VS Code settings
├── host/              # Python host control interface
│   ├── synth_control/ # Python control library
│   ├── examples/      # Usage examples
│   ├── .devcontainer/ # Python development container
│   └── .vscode/       # Python-specific VS Code settings
├── tools/             # Shared utilities and scripts
└── .vscode/           # Root workspace configuration

Build & Flash

Firmware (ESP32)

Navigate to the firmware directory and use ESP-IDF:

cd firmware
idf.py build
idf.py -p /dev/ttyUSB0 flash

Or use the convenient script for multiple devices:

./tools/flash_multiple.sh

Host Control (Python)

A Python interface is provided for programmatic control:

cd host
python3 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

# Run examples
python examples/basic_control.py
python examples/harmonic_sweep.py

UART Usage

Connect to the ESP32 UART (default 115200 baud) and type commands as described above. Type help for a list of commands.

Linux commands to test UART

# Generate a square wave on Channel A at 50Hz
printf "wha3,33\r" > /dev/ttyUSB1
printf "wha5,20\r" > /dev/ttyUSB1
printf "wha7,14\r" > /dev/ttyUSB1
printf "wha9,11\r" > /dev/ttyUSB1
printf "wha11,9\r" > /dev/ttyUSB1
printf "wha13,8\r" > /dev/ttyUSB1
printf "wha15,7\r" > /dev/ttyUSB1
printf "wha17,6\r" > /dev/ttyUSB1

# Clear all harmonics for Channel A and B
printf "whcla\r" > /dev/ttyUSB1
printf "whclb\r" > /dev/ttyUSB1

# Rolling harmonic phase for Channel A and B
ph=-180
while true; do
    printf "wha5,20,%d\n" "$ph" > /dev/ttyUSB1
    invph=$((ph * -1))
    printf "whb3,10,%d\n" "$invph" > /dev/ttyUSB1
    sleep 0.03
    ph=$((ph + 1))
    if [ "$ph" -gt 180 ]; then
        ph=-180
    fi
done

Development

VS Code Workspace

Open the multi-root workspace for unified development:

code .vscode/NHP_Synth.code-workspace

DevContainers

Each component has its own development container:

• Firmware: ESP-IDF container with all tools
• Host: Python container with analysis libraries

Tools

• tools/flash_multiple.sh - Flash firmware to multiple devices
• tools/uart_test.py - Test UART communication

File Structure

• firmware/main/main.c: Main ESP32 application source
• firmware/build/: Build artifacts (ignored by git)
• host/synth_control/: Python control library
• host/examples/: Python usage examples
• tools/: Shared utilities and scripts
• .gitignore: Excludes build and config files from version control

License

MIT License (or specify your license here)