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円" 
 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?

• Majenko: There is no such thing as a hex array. Everything is all just numbers. Even letters are numbers. Your string is already an array.
• Juraj: Serial.print("TOPWAY"); should do it
• mehmet: @Juraj you mean like that for total query like above: Serial.write(0xaa); Serial.write(0x42); Serial.write(0x00); Serial.write(0x00); Serial.write(0x00); Serial.write(0x80); Serial.print("TOPWAY"); Serial.write(0x00); //string end with "0円" Serial.write(0xcc); Serial.write(0x33); Serial.write(0xc3); Serial.write(0x3c); . if Not? please show me as answer not in comment.
• Juraj: the answer is below

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);
}

• Edgar Bonet: 1. Instead of writing a loop, you can DISPLAY_DEVICE.write(displayPktStart, sizeof displayPktStart);, and likewise for displayPktEnd. 2. You mean DISPLAY_DEVICE.print(text);, not println(). 3. Serial.print() will not send the terminating 0円, you may want to add that to displayPktEnd.
• voidPointer: @EdgarBonet Thanks. Updated.
• mehmet: Thanks A lot. I've added DISPLAY_DEVICE.begin(9600); in setup
• voidPointer: @mehmet I hope my update matches your expectations.
• mehmet: @voidPointer well, I don't want to bother you too much, but I have one more question. if I want to use dynamic address, such as "000080" instead of Serial.write(0x00); Serial.write(0x00); Serial.write(0x80); how to add this method, like writeDisplay(msg, "000080")