OG code

    #include <Time.h>

    // Simple macro for inverted pwm output (since my circuit will turn the lamp OFF whenever the output is HIGH)
    #define _analogWrite(a, b) analogWrite(a, 255-(b))

    // Globals
    const PROGMEM int pwmPin = 3;
    time_t lastUpdate = 0;
    int pwmValue = 0;

    void setup() {
        Serial.begin(9600);
        Serial.setTimeout(250);
        pinMode(pwmPin, OUTPUT);
        _analogWrite(pwmPin, pwmValue);
    }

    void loop() {
        // Get current time
        time_t currentTime = now();

        // If there's data available, process it
        if (Serial.available()) {
            // Read all the incoming data
            String str = Serial.readString();
            // Extract only the numbers from it
            String str2 = "";
            for (int i=0; i<str.length(); i++) {
                if (str[i] >= '0' && str[i] <= '9') str2 += str[i];
            }
            // Convert it to an int, and store it
            pwmValue = str2.toInt();
            // Save the current time
            lastUpdate = currentTime;
        }

        // Safety mechanism (if we haven't received anything in the last 30 seconds, set the output to 0)
        if (currentTime - lastUpdate > 30) pwmValue = 0;

        // Write the value we have to the output
        _analogWrite(pwmPin, pwmValue);

        delay(100);
    }