Question

I am doing a project with an arduino to make a bell ring, and when I first tried, it worked how I wanted it to (wait(Serial.read())), but now I need to send over 100 0‘s over the serial port just to make it show for 4 seconds. Here is my Java code:
prepare for longness

Main.ringBell("100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000");

public static void ringBell(String length) throws Exception {
     output.write(length.getBytes());
     output.flush();
}

Here is the Arduino sketch:

int ledPin = 13;

void setup() {
    pinMode(ledPin, OUTPUT);
    Serial.begin(9600);
}

void loop() {
    if(Serial.available() > 0) {
        digitalWrite(ledPin, HIGH);
        delay(Serial.read());
        digitalWrite(ledPin, LOW);
    }
}

Does anyone see a error in my code? If so, please just let me know what’s wrong and I’ll fix it.

Thank you.

Answer 1

You are not sending one big number to the arduino but several ASCII bytes. The Arduino will see this sequence:

49, 48, 48, 48, 48, 48, ...

In each loop it will read one byte and wait for that number of milliseconds. 49 or 48 milliseconds are not a long time. So what you have is a constant flicker of the LED which is to fast to see with the eye.

The next thing is: You are sending the bytes in one flush. But the Arduino has only a small internal buffer of 64 byte (see available docu). The rest is simply forgotten.

Lets calculate roughly: 64 bytes * (48 ms delay per byte ) is 3072ms. Yes, this sounds plausible.

Next thing would be: delay only can handle arguments of type unsigned long which is 32 bit which translates to ~4,000,000,000 milliseconds you can wait. Your argument in Main is way beyond this limit.

So: The easiest thing is to use parseInt instead of read. And in Main supply only numbers in the range of a positive int (0.. 32767). And also do some delays in your Main before sending the next ringBell.