Hi, I have got a strange bug.
I bought Arduino nano clone for less than $2 with the CH340 USB serial converter to see if it is even possible - I thought the ATMega alone costs more (it definitely does in our local store). Everything looks fine apart from one thing.
I need to have Serial Monitor opened for the Arduino to work - even if Serial is not used at all. If I close the Serial Monitor the Arduino stops doing whatever it does and start blinking the "L" LED regularly with about 1 or 2 Hz frequency. When I open the Serial Monitor again the sketch runs as expected (I know it restarts the Arduino) and after closing it the blinking starts again. There is my minimal example:
void setup() {
pinMode(13, OUTPUT);
digitalWrite(13,LOW);
pinMode(8, OUTPUT);
}
void loop() {
digitalWrite(8,HIGH);
delay(1000);
digitalWrite(8,LOW);
delay(100);
}
With Serial Monitor open the LED connected to pin 8 is blinking while onboard LED is off. As soon as I close Serial Monitor the external LED turns off while the onboard LED is blinking (with duty cycle approx 5-10%).
Thanks for any advice!
EDIT: I tried measuring voltages on pins. In general voltages are the same as on my (working) UNO: stable 5V is on 5V output and TX and RX pins (digital 0 and 1), on pin 13 is alterning 0 and 5 (as the LED is blinking), all other I/O pins are floating.