How to convert a String to Hex array

Question

I am trying use a HMI display. If I want to send a data, for example I want to write "TOPWAY" to 0x00000080 address it should like that:

    Serial.write(0xaa); // packet head
    Serial.write(0x42); // VP_N16 string write command
    Serial.write(0x00); // VP_N16 address
    Serial.write(0x00);
    Serial.write(0x00);    
    Serial.write(0x80); 
    Serial.write(0x54); //T
    Serial.write(0x4f); //O
    Serial.write(0x50); //P
    Serial.write(0x57); //W
    Serial.write(0x41); //A
    Serial.write(0x59); //Y
    Serial.write(0x00); //string end with "\0" 
    Serial.write(0xcc); // packet tail
    Serial.write(0x33); // packet tail
    Serial.write(0xc3); // packet tail
    Serial.write(0x3c); // packet tail

I want to make a method like SendString(String abc) to send that like above. I need convert string a hex array and call in Serial.write(array[i]). Can you hep me?

Answer 1

I don't know anything about the particular display, but based on the information provided I hope this is at least shows the foundation of one way you could approach a final solution.

Update:

• Incorporated great improvements and a fix from Edgar in the comments.
• String overload.
• Display baud rate suggested by mehmet

#define DISPLAY_DEVICE Serial
#define DISPLAY_DEVICE_BAUD 9600

static uint8_t displayPktStart[] = {
    0xaa, // packet headchar
    0x42, // VP_N16 string write command
    0x00, // VP_N16 address
    0x00, // ...Fill
    0x00,
    0x80
  };

static uint8_t displayPktEnd[] = {
    0x00, // End of text
    0xcc, // packet tail
    0x33, // packet tail
    0xc3, // packet tail
    0x3c // packet tail
  };


void writeDisplay(const char* text)
{
  // Write packet headers
  DISPLAY_DEVICE.write(displayPktStart, sizeof displayPktStart);

  // Send text
  DISPLAY_DEVICE.print(text);

  // Write packet tail
  DISPLAY_DEVICE.write(displayPktEnd, sizeof displayPktEnd); 
}

void writeDisplay(const String& text)
{
  writeDisplay(text.c_str());
}

void setup()
{
  DISPLAY_DEVICE.begin(DISPLAY_DEVICE_BAUD);
}

void loop() 
{
  String msg = "TOPWAY";
  writeDisplay(msg);

  delay(2000);
  writeDisplay("Peanuts taste like chicken");
  delay(500);
  writeDisplay("");
  delay(1000);
  writeDisplay("No. Seriously");
  delay(2000);
}