I am trying to make a connection between 2 Arduino's with the APC220 rf modules.

void setup() {

void loop() {
   int value = 5;

I uploaded this code to my Arduino Nano and Uno. I disconnected the rf modules for uploading the code.

I tried to run this program with an external power source (lipo 11.1V 2200mAh). The Arduino is powered on(power led is on) BUT the tx led doesn't blink.

The only way to make it work is by using the usb and opening the serial monitor on my pc.

I tried to use a 10k resistor between tx and rx (or rx to ground) but the code won't run...

Can someone help me?

Solution : the arduino worked perfect. When you connect the arduino with an exernal power supply the tx and rx lights won't light up, Even when they are transmitting or receiving.

  • 1
    You'll want to add your solution as an answer and select it. Also, the TX and RX LEDs are generally only for the USB connection, which includes the serial monitor. Jun 2, 2015 at 9:12
  • your Arduino's has to have common ground also.
    – Martynas
    Jun 2, 2015 at 9:56
  • Is it an official arduino board? Which type?
    – Paul
    Jun 2, 2015 at 13:29

2 Answers 2


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.


I think tx not activated without available serial connection. What is you rf module and what is the baud rate of RF module. Also can you share connection diagram or a test video. Alternativeliy you can look SoftwareSerial: http://www.arduino.cc/en/Reference/SoftwareSerial

  • I set the baudrate of both the apc220's to 9600 with rf magic. I don't want to use software serial because I need the storage space of the tx and rx.
    – Michael
    May 23, 2015 at 13:30

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