I have a simple HTTP server that monitors a serial port and responds to HTTP requests by sending the value. The serial port constantly outputs data, so that apart from a brief moment when the device is initializing the Arduino always has data available. Once a value is retrieved from the RS232 connection it is stored in a buffer. The buffer is overridden when new values are received.

Occasionally the server does not respond to a request. Monitoring through Chrome developer tools reports net::ERR_CONNECTION_RESET Could it be that the Arduino is busy with processing the serial port when the connection request is made? What I find very difficult to understand is that once in a while the code below will display "Not available". This shouldn't happen because, as stated above, the buffer is always available.

    client.println("HTTP/1.1 200 OK");
    client.println("Content-Type: text/html");
    client.println("Connection: close");
    client.println("Cache-Control: no-cache, no-store, must-revalidate");
    client.println("Pragma: no-cache");
    client.println("Expires: 0");
    client.println("Refresh: 5");
    client.println("<!DOCTYPE HTML>");
    client.print("Value: ");
    if (valueReady()) {
      client.println( getValue() );
    } else {
      client.println( "Not available" );

The "Not available" message is really confusing because that should only occur when the Arduino starts. valueReady() will only return false when power is first applied.

The LEDs on the Ethernet shield do not indicate that the Arduino is being reset, but it seems as if the sketch is periodically restarting. Is it possible for a buffer overrun to cause the Arduino to reboot?

1 Answer 1


The delay was occurring because, in some cases, I was storing the RS232 data into a character array past the initialized length. It looks like it was causing the Arduino to reboot.

  • It's often a good practice to send debug information (flashing LED's or sending a string) at startup. The vaguest problems (, power issues and some memory issues) can be spottend this way.
    – aaa
    Commented Apr 7, 2016 at 5:31

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