Arduino funtioning whitout serial monitor software

I have a question....

I have a program code uploaded to an arduino but this code no execute or operate after open de serial monitor of arduino software.

I can fix this issues??? Or is normal and is a rule open de serial monitor ever


It's not normal so there is possibly something wrong with code you haven't shown us or the connections to the Arduino that you've said nothing about.

Do you have anything connected to pins 0 and 1, the hardware serial pins?


If your code has in it:-

while (!Serial) { }

Then it will not run without the connection to a serial port.

But hey, who knows unless you post your code.

Or is normal and is a rule open de serial monitor ever

No it is not normal, an Arduino can work without a serial port connection.

Thanks for the responses, and it is my code ( is very simple and basic for the moment but i try to conect to arduino via telnet over the CMD of windows and is imposible to connect and show the text in screen before open serial monitor):

nclude <SPI.h>
#include <Ethernet.h>

byte mac = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
byte ip = {192, 168, 1, 7 };
byte gateway = {192, 168, 1, 1 };
byte subnet = {255, 255, 255, 0 };

boolean connectFlag = 0;

unsigned long timeOfLastActivity;
unsigned long allowedConnectTime = 300000;

EthernetServer server(23);
EthernetClient client = 0;

void setup()

for(int i= 0; i < 10; i++) pinMode(i, OUTPUT);

Ethernet.begin(mac, ip, gateway, subnet);

void loop()
// look to see if a new connection is created,
// print welcome message, set connected flag
if (server.available() && !connectFlag) {
connectFlag = 1;
client = server.available();
client.println(“hello world");
client.println("? for help");

What Happend? :frowning:

Which Arduino board are you using?


I am using a arduino uno whit a Ethernet shield... the access for telnet via utp cable is functioning but olny if start the serial monitor, if not the connection and the show “hello word” is not perform.

The only thing I can think is that when you open Serial Monitor it resets the Uno. Maybe that reset is somehow needed?

Mmmm is posible, Maybe. I try other options today and I will tell you how it was!