Serial Connection of Arduino UNO to an old digital scale through the printer port

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I am a little lost. I tried using the diode and resistors from runaway_pancake. Still not working. I am not understanding how to use the TTL. It is a simople pinout for the scale. I changed the code around.

#include <SoftwareSerial.h>

SoftwareSerial scaleSerial(8,9); // RX, TX - adjust the pin numbers as needed
String incomingLine = "";

void setup() {
    Serial.begin(2400); // Set baud rate for the Serial Monitor
    scaleSerial.begin(2400);

    Serial.println("Setup complete. Waiting for incoming data...");
}

void loop() {
    if (scaleSerial.available()) {
        char incomingByte = scaleSerial.read();

        if (incomingByte == '\r' || incomingByte == '\n') {
            Serial.println("Received End of Line. Processing...");
            processCustomFormat();
        } else {
            incomingLine += incomingByte;
        }
    }

    // Your main code here, without delay
}

void processCustomFormat() {
    if (incomingLine.length() >= 15) {
        Serial.println("Processing Custom Format...");

        String header = incomingLine.substring(0, 2);
        String separator = incomingLine.substring(2, 3);
        String polaritySign = incomingLine.substring(3, 4);
        String weightData = incomingLine.substring(4, 12);
        String unitOfMeasure = incomingLine.substring(12, 15);

        Serial.println("Hello, Print Part of Program!");
        Serial.print("Header: ");
        Serial.println(header);
        Serial.print("Separator: ");
        Serial.println(separator);
        Serial.print("Polarity Sign: ");
        Serial.println(polaritySign);
        Serial.print("Weight Data: ");
        Serial.println(weightData);
        Serial.print("Unit of Measure: ");
        Serial.println(unitOfMeasure);
        Serial.println();
    } else {
        Serial.println("Incomplete or invalid line. Discarding...");
    }

    // Clear the accumulated line for the next iteration
    incomingLine = "";
}

I get the message "Setup complete, waint for incoming data" , so the program is at least reading. Obviously have no incoming data.