battery / external power supply


i experince some strange behaviour when i try to power arduino via battery or other external power supply. as long as my external supply is around 5V everything is working. when i go over it (like 9v battery) the RX TX leds also start to light up - slowly depending on the voltage. until ca. 5.5 V they are dark. i tested 3 boards so far - same behaviour - is this really supposed to be ?

any idea


Hi erich

Yes it's a strange behaviour but harmless. It is due to the fact that, when the usb is unplugged, the LEDs are still powered at 5 volts but the chip they are connected to isn't. This means that the cathodes are "floating" and the LED might flicker.

This has been changed in future productions where the LEDs will be powered by the USB bus so when the board is not plugged into the computer the LED will be always off.

As I said before it's harmless.