Problem in using Rx and Tx pins for serial Communication

Hello,
I want to use the external Rx and Tx pins Arduino uno board to perform serial communication. The problem with my system is that when i turn on my controller using an external power, it doesn't starts the communication automatically, while if it is connected with my system and i start the serial monitor than it starts transmitting the data.
Since i want to place it in my original board, i want the controller to start performing serial communication automatically when the power is turned on using an external adapter.
Regards

I guess publishing your code might be a good idea, not to mention a clearer expression of what you are trying to connect to. but the first issue is - how do you know if it is not transmitting data in the first instance? Maybe it is and you can't tell. The fact that it does when you connect the serial monitor rather suggests this, or your external power is inadequate. When you connect the serial monitor you reset the Arduino. It sounds rather like a wiring problem Tx to Rx, and Rx to Tx.

Thanks alot for replying. The problem is on any program, even any basic program that runs perfectly.
Regarding power, it doesnt matter too, for e.g if i power through usb, it doesnt works too.
Actually the Tx pin led present on the Arduino board doesn't blink when when it communicates with my system, which does blinks when a serial monitor starts.

Post a program that demonstrates the problem you would like to solve. (Preferably a short program)

Then we may understand what you are talking about.

...R

It sounds to me that you are using an Arduino with a USB interface, perhaps the UNO. In this case Tx and Rx leds won't light as they are lit by outputs from the USB interface. If you are trying to communicate via the 0and 1 pins of the arduino that is not using the USB and those leds won't light. The other problem is that the Arduino tx and rx are connected to the tx and rx pins on that USB chip, there are series resistors to isolate them a bit but you do need to drive them in both directions and not just have pullups or the USB chip will win. You are driving at logic levels aren't you and not the +/-12Volt swing of a serial port on for example a PC, that will blow your Arduinos inputs and on the transmit side the logic level swing of the arduino will not go to a -ve voltage and so won't work.

oh, ok, it wasnt error i was focusing the Tx led, which glows on transmission but it was not blinking so i was thinking that its not working, but i was sending the data to the serial port.
So thanks everyone for helping me.
Regards

One other point if you have anything connected to the Tx and Rx (0 and 1) you need to disconnect them before you upload code or the upload will fail as the USB chip won't be able to drive against those other connections.

he other problem is that the Arduino tx and rx are connected to the tx and rx pins on that USB chip, there are series resistors to isolate them a bit but you do need to drive them in both directions and not just have pullups or the USB chip will win.

That is some what hit or miss. I've had two arduinos connected tx/rx/gnd with separate IDE serial monitors running for each. I added a diode on the slave arduino tx line so it would not hold the master arduino rx high and that seemed to correct the bi directional communication issues. There is no way to isolate the tx on the arduino USB serial interface, but the communications seemed to work ok with just the slave diode.

In fact if your program is going to use the serial connection and you use the USB only to upload its simpler to use a mini or a mini pro which doesn't have the usb and also costs less and is smaller