Arduino won't send serial data if connected with external power supply
Solution : The Arduino worked perfectly. When you connect the Arduino with an external power supply the Tx and Rx lights won't light up, Even when they are transmitting or receiving.



I'm adding this as the solution to stop this being re-added as an unsolved problem.



That is correct. The Tx and Rx LEDs are connected to the Atmega16U2 processor, and thus only flash if there is serial comms via USB.