To AWOL: my application is actually more complicated, as it involves also a buzzer and an external LED, but the problem stays. I'm powering it form USB.
To Grumpy_Mike: I tried to disable watchdog as following, but the problem remains:
#include <avr/wdt.h>
int led = 13;
ISR (WDT_vect)
{
wdt_disable();
}
void setup() {
pinMode(led, OUTPUT);
}
void loop() {
digitalWrite(led, HIGH);
}
I tried also just putting command wdt_disable in the void loop() but doesn't solve the problem!