Full-Duplex Radio System Design
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I can guide the design, but I’m currently unable to modify the Flux project directly because execution credits are unavailable. The project is still empty: 0 components and 0 nets.
Recommended architecture for two identical full-duplex stations:
- Controller: Arduino Nano, 5 V logic
- RF link: nRF24L01+ PA/LNA module at 3.3 V
- Microphone: MAX4466 electret microphone preamp module, powered from 5 V or 3.3 V depending on the module
- Speaker driver: PAM8403 class-D amplifier preferred over LM386 for better efficiency and volume from 5 V
- Power: 5 V input for Arduino/audio amp, dedicated 3.3 V regulator for the nRF24L01+ PA/LNA
- Audio output method: Arduino PWM pin with RC low-pass filter into the PAM8403 input
- Audio input method: microphone output into an Arduino analog input
Important design note: true live full-duplex audio is demanding for an Arduino Nano. It has limited RAM, ADC speed, PWM quality, and processing headroom. It can work as a low-bitrate voice intercom with aggressive sampling/compression, but audio quality and latency will be limited. For better results, ESP32 or a dedicated audio codec/radio architecture would be stronger.
Suggested schematic connections:
nRF24L01+ PA/LNA to Arduino Nano:
Table
| nRF24L01+ pin | Arduino Nano pin | Notes |
|---|---|---|
| VCC | 3.3 V regulated rail | Do not power from Nano 3.3 V pin if using PA/LNA |
| GND | GND | Common ground required |
| CE | D9 | Configurable GPIO |
| CSN / CS | D10 | SPI chip select |
| SCK | D13 | SPI clock |
| MOSI | D11 | SPI MOSI |
| MISO | D12 | SPI MISO |
| IRQ | D2 optional | Interrupt input, optional |
Power warning: many nRF24L01+ PA/LNA modules tolerate 5 V SPI logic, but the IC itself is 3.3 V. For a robust schematic, add logic level shifting or at least series resistors on Arduino-to-radio lines: SCK, MOSI, CE, CSN. MISO from radio to Nano is usually read correctly as HIGH at 3.3 V.
Microphone module:
Table
| MAX4466 module pin | Arduino Nano |
|---|---|
| VCC | 5 V or 3.3 V per module rating |
| GND | GND |
| OUT | A0 |
Audio amplifier:
Table
| PAM8403 pin | Arduino Nano / power |
|---|---|
| VCC | 5 V |
| GND | GND |
| IN+ / L-IN | PWM audio after RC filter, e.g. D3 |
| IN− / signal GND | GND or module input ground |
| Speaker outputs | Speaker only, do not connect to GND |
PWM audio filter recommendation:
- Arduino D3 PWM → 1 kΩ resistor → amplifier input
- 10 nF capacitor from amplifier input to GND
- Optional volume potentiometer between filter output and amp input
Decoupling capacitor placement:
Table
| Location | Capacitors | Placement |
|---|---|---|
| nRF24L01+ PA/LNA VCC-GND | 100 nF ceramic + 10 µF to 47 µF electrolytic/ceramic | Directly beside RF module power pins |
| 3.3 V regulator input | Per regulator datasheet, commonly 1 µF to 10 µF | Close to regulator input pin |
| 3.3 V regulator output | Per regulator datasheet, commonly 1 µF to 10 µF | Close to regulator output pin |
| Arduino 5 V rail | 100 nF + 10 µF bulk | Near Nano 5 V/GND pins |
| PAM8403 VCC-GND | 100 nF ceramic + 470 µF bulk recommended for speaker current pulses | Close to amplifier module |
| Microphone VCC-GND | 100 nF ceramic | Close to microphone module |
| Analog mic signal | Optional 100 Ω series + small capacitor if noise is present | Near Arduino analog input |
What remains to be done when execution is available:
- Rename the project from its draft name and create a short design specification.
- Select exact library parts/modules for Arduino Nano, nRF24L01+ PA/LNA, MAX4466 mic, PAM8403 amp, 3.3 V regulator, passives, and connectors.
- Check datasheets/module pinouts before wiring.
- Create the schematic with:
- Arduino Nano block
- RF transceiver block
- Microphone input block
- PWM audio output/filter block
- Audio amplifier/speaker block
- 5 V and regulated 3.3 V power block
- Add all decoupling and bulk capacitors.
- Verify ERC/power rails and confirm no unresolved schematic violations.
- Only after schematic verification, proceed to PCB placement and routing.
Find library parts
Add 3.3V regulator
List schematic nets
Precheck architecture
Save design note
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