led matrix via web steuern (Anfänger)

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Guten Tag,

ich möchte gerne eine 8x8 Led Matrix via Web steuern.
Ich verwende 1 x UNO und 1 X Ethernet Shield und 1 x Adafruit_8x8matrix.
Vom Prinzip habe ich es fast fertig.
So sieht mein Code bisher aus:

#include <SPI.h>
#include <Ethernet.h>
#include <Wire.h>
#include "Adafruit_LEDBackpack.h"
#include "Adafruit_GFX.h"

Adafruit_8x8matrix matrix = Adafruit_8x8matrix();

byte mac[] = { 
  0x90, 0xA2, 0xDA, 0x0E, 0xFE, 0x92 };
byte ip[] = { 
  192,168,2,108 };
byte gateway[] = { 
  192,168,1, 1 };
byte subnet[] = { 
  255, 255, 0, 0 };
EthernetServer server(80); //server port
String readString;


void setup(){

  //start Ethernet
  Ethernet.begin(mac, ip, gateway, subnet);
  server.begin();
  Serial.begin(9600);
  Serial.println("Arduino ist waitung for matrix data"); 

  matrix.begin(0x70);  // pass in the address
  matrix.setBrightness(15); // 0 to 15
  matrix.blinkRate(0);
}

void loop(){
  // Create a client connection
  EthernetClient client = server.available();
  if (client) {
    while (client.connected()) {
      if (client.available()) {
        char c = client.read();

        //read char by char HTTP request
        if (readString.length() < 100) {

          //store characters to string
          readString += c;
          //Serial.print(c);
        }

        //if HTTP request has ended
        if (c == '\n') {


          Serial.println(readString); //print to serial monitor for debuging

          client.println("HTTP/1.1 200 OK"); //send new page
          client.println("Content-Type: text/html");
          client.println();


          delay(1);
          //stopping client
          client.stop();


          String matrix_daten = splitString(readString,'@',1);
          
//---------------------- aus dem String matrix_daten soll folgendes entstehen
static const uint8_t PROGMEM
  smile_bmp[] =
  { B00111100,
    B01000010,
    B10100101,
    B10000001,
    B10100101,
    B10011001,
    B01000010,
    B00111100 };    
//----------------------

          matrix.clear();
          matrix.drawBitmap(0, 0, smile_bmp, 8, 8, LED_ON);
          matrix.setBrightness(1);
          matrix.writeDisplay();  

          //clearing string for next read
          readString="";

        }
      }
    }
  }
}


String splitString(String s, char parser,int index){
  String rs='\0';
  int parserIndex = index;
  int parserCnt=0;
  int rFromIndex=0, rToIndex=-1;

  while(index>=parserCnt){
    rFromIndex = rToIndex+1;
    rToIndex = s.indexOf(parser,rFromIndex);

    if(index == parserCnt){
      if(rToIndex == 0 || rToIndex == -1){
        return '\0';
      }
      return s.substring(rFromIndex,rToIndex);
    }
    else{
      parserCnt++;
    }

  }
  return rs;
}

Nun sollen die Matrixdaten über ein URL übermittelt werden:
http://192.168.2.108/?@ B00111100,B01000010,B10100101,B10000001,B10100101,B10011001,B01000010,B00111100@

Diesen stehen auch schon in der Variable matrix_daten bereit.

Wie kann ich diese jetzt weiterverarbeiten, damit sie in dieser Zeile Verwendung finden:
matrix.drawBitmap(0, 0, smile_bmp, 8, 8, LED_ON);

Über Hilfe freue ich mich
Grüße
Christoph