VTXControl

Arduino library providing video transmitter (VTX) control via SmartAudio and Tramp protocols.

Supports switching power levels, channels/frequencies, and PitMode on VTX modules from Arduino-based systems (AVR, ESP32, etc.).

Protocol implementations derived from BetaFlight and ArduPilot. Serial transport uses SoftwareSerialWithHalfDuplex (AVR, interrupt-driven) or ESP32HalfDuplex (ESP32, polling bit-banged), selected automatically at compile time.

• Polling RX — available() busy-waits up to 150ms for the first byte, then 5ms between subsequent bytes. No ISR dependency.
• Bit-banged TX — GPIO driven directly with wait_us() delays.
• Line settling — listen() inserts a 1ms delay after TX to suppress false start bits from line ringing.
• Buffer drain — flush() clears the circular buffer and waits for idle line (≥10ms).

Byte-index based parsing replaces the packed-struct reinterpret-cast that had wrong alignment:

AA 55 CMD LEN [VER] [CH] [PW] [MODE] [FREQ_H] [FREQ_L] ... [CRC]
              [4]   [5]   [6]   [7]

Fixes silent misconfiguration where buffer[4] (version byte) was previously read as the channel index.

#include <VTXControl.h>

const uint16_t powers[] = {25, 200, 400, 800};
const uint16_t freqs[] = {
  5865, 5845, 5825, 5805, 5785, 5765, 5745, 5725,  // Band A
  5733, 5752, 5771, 5790, 5809, 5828, 5847, 5866,   // Band B
  5705, 5685, 5665, 5645, 5885, 5905, 5925, 5945,   // Band E
  5740, 5760, 5780, 5800, 5820, 5840, 5860, 5880,   // Fatshark
  5658, 5695, 5732, 5769, 5806, 5843, 5880, 5917,   // Race
};

VTXControl vtx(SmartAudio, 17, powers, 4, freqs, 40);

void setup() {
  Serial.begin(115200);
  if (vtx.updateParameters())
    vtx.setPitMode(false);       // ensure VTX is transmitting
}

void loop() {
  vtx.setChannel(0);             // 5865 MHz
  vtx.setPower(1);               // 200 mW (index 1)
  delay(1000);
  vtx.setChannel(39);            // 5917 MHz
  delay(1000);
}

VTXControl vtx(Tramp, 53, powers, 4, freqs, 40);

void setup() {
  Serial.begin(115200);
  vtx.updateParameters();
}

VTXControl(
  int vtxMode,                  // SmartAudio or Tramp
  int softPin,                  // GPIO pin for half-duplex communication
  const uint16_t powers[],      // power levels in mW
  int powers_len,               // number of power levels
  const uint16_t freqs[],       // frequency table in MHz
  int freqs_len,                // number of frequencies
  int responseTimeOut = 1000,   // response timeout per poll (ms)
  bool smartBaudRate = true,    // auto-scan baud rates on failure
  int numtries = 3              // retries before changing baud rate
);

• SmartAudio uses 4800 baud (or auto-detected, typically ~4980 baud), 8N2
• Tramp uses 9600 baud, 8N1
• PitMode is supported for SmartAudio only (not Tramp)
• Temperature query (GetSensor) for Tramp is parsed but not exposed
• CRC verification can be disabled via SMARTAUDIO_IGNORE_CRC in VTX_SmartAudio.h
• Eachine TX5258 and similar clones may need SMARTAUDIO_WRITE_ZEROBYTES_AT_THE_END set to true
• Use the VTX_Test sketch to diagnose unknown VTX models

The VTX_Test/ folder contains a diagnostic sketch that can:

• Send arbitrary SmartAudio commands
• Analyze VTX responses
• Try different baud rates
• Dump raw response bytes

Use this to characterize a new VTX before integrating.

ESP32HalfDuplex and SoftwareSerialWithHalfDuplex are LGPL 2.1. The remainder of VTXControl is GPL 3.0 — see LICENSE file.