Why does TX stop when on battery power?

Projects Programming
1

I have a program running fine when connected to USB (UNO). When I disconnect, the LED (#13) keeps working but the TX light stops...WHY?

void setup() {
// put your setup code here, to run once:
Serial.begin(9600); // Start serial Serial at 9600 baud
}

void loop() {
// put your main code here, to run repeatedly:
delay(1000);
Serial.write("test");
digitalWrite(13, HIGH); // set the LED on
delay(1000); // wait for a second
digitalWrite(13, LOW); // set the LED off
delay(1000); // wait for a second
}

2

Well, if you disconnect the USB cable, there would be no more transmit or receive signals, so it make sense that tx goes out. Your sketch tells the led to blink on and off, whether or not the USB cable is connected, assuming you are powering the arduino from a wall wort or battery.

3

Serial data is still being transmitted out the arduino tx pin, just not out the usb serial convertor because there is no attachment to the PC usb and the serial converter chip is what drives the send and receive leds. Check with a scope on pin 1 and I'm sure you will see the data still being sent out every two seconds.

Lefty