Changing the frequency in VTX akk alpha via ESP32?

Maybe someone has a code example or knows how to switch the frequency on akk alpha via esp32. I currently have VTX akk alpha 25w.

I have already tried all possible options, but I got to the point that the desired frequency turns on for 1 second, and then resets to factory settings.

I'm using an EPS32 esp32 ttgo t-display. But I don't think the problem is due to the board's hardware.

What's strange is that there's a response to changing the frequency, but for some reason the VTX immediately resets the frequency to the one I manually set using the button on the VTX.

I apologize in advance for my English) I would be glad to any help.

Code:

#include <HardwareSerial.h>

#ifndef SA_TX_PIN
#define SA_TX_PIN 17
#endif

// BOSCAM A/B/E стандартні частоти (МГц)
static const uint16_t VTX_FREQ[3][8] = {
  {5865, 5845, 5825, 5805, 5785, 5765, 5745, 5725}, // A
  {5733, 5752, 5771, 5790, 5809, 5828, 5847, 5866}, // B
  {5705, 5685, 5665, 5645, 5885, 5905, 5925, 5945}  // E
};

static HardwareSerial SA(2);

static uint8_t currentBand = 0;
static uint8_t currentChannel = 0;
static bool switchedOnce = false;
static unsigned long startMs = 0;
static unsigned long lastFreqSet = 0;

static uint8_t crc8_d5(const uint8_t *data, size_t len) {
  uint8_t crc = 0x00;
  for (size_t i = 0; i < len; i++) {
    crc ^= data[i];
    for (int b = 0; b < 8; b++) {
      if (crc & 0x80) crc = (uint8_t)((crc << 1) ^ 0xD5);
      else crc <<= 1;
    }
  }
  return crc;
}

// Коди команд SmartAudio (часто зустрічаються у v2/v2.1)
#define SA_CMD_SET_FREQUENCY  0x03

static void saRebegin(uint32_t config, bool invert) {
  SA.end();
  SA.begin(4800, config, -1, SA_TX_PIN, invert);
}

static void saWriteFrameOnce(const uint8_t *frame, uint8_t framelen) {
  SA.write((uint8_t)0x00); // префікс для притиску лінії вниз
  delay(2);
  SA.write(frame, framelen);
  SA.write((uint8_t)0x00); // суфікс нульовим байтом
  SA.flush();
}

static void saSend(uint8_t cmd, const uint8_t *payload, uint8_t len) {
  uint8_t frame[4 + 8 + 1];
  frame[0] = 0xAA;
  frame[1] = 0x55;
  frame[2] = cmd;
  frame[3] = len;
  for (uint8_t i = 0; i < len; i++) frame[4 + i] = payload ? payload[i] : 0x00;
  uint8_t crc = crc8_d5(&frame[2], 2 + len);
  frame[4 + len] = crc;
  uint8_t framelen = 5 + len;

  // Використовуємо тільки один формат: 8E2, без інверсії
  saRebegin(SERIAL_8E2, false);
  saWriteFrameOnce(frame, framelen);
  delay(20);
  saWriteFrameOnce(frame, framelen);  // Повтор для надійності
}

// Встановити частоту напряму (МГц, little-endian)
static void saSetFrequency(uint16_t mhz) {
  uint8_t payload[2] = { (uint8_t)(mhz & 0xFF), (uint8_t)((mhz >> 8) & 0xFF) };
  saSend(SA_CMD_SET_FREQUENCY, payload, 2);
}

void setup() {
  Serial.begin(115200);
  SA.begin(4800, SERIAL_8E2, -1, SA_TX_PIN, false);
  Serial.println("SmartAudio init");

  // Початково: A CH3 (індекс 2)
  currentBand = 0;       // A
  currentChannel = 2;    // CH3
  saSetFrequency(VTX_FREQ[currentBand][currentChannel]);
  Serial.println("Set A CH3 via frequency");
  startMs = millis();
}

void loop() {
  // Перевіряємо, чи потрібно перемкнути частоту
  if (!switchedOnce && (millis() - startMs >= 10000UL)) {
    currentBand = 0;    // A
    currentChannel = 7; // CH8
    saSetFrequency(VTX_FREQ[currentBand][currentChannel]);
    Serial.println("Switched to A CH8");
    switchedOnce = true;
  }

  // Періодично оновлюємо частоту, щоб "утримувати" її
  if (millis() - lastFreqSet > 1000UL) {  // Кожну секунду
    saSetFrequency(VTX_FREQ[currentBand][currentChannel]);
    lastFreqSet = millis();
  }
}