Troubleshooting#upload

#include <LiquidCrystal.h>

#define DIODE_DROP 0.7

LiquidCrystal lcd(13, 12, 11, 10, 9, 8);

void setup()
{
lcd.begin(16, 2);
lcd.print(“Battery voltage:”);
}

void loop()
{
float voltage = analogRead(A0) / 1024.0 * 10.0;
if (voltage > 0.1)
voltage += DIODE_DROP;

lcd.setCursor(0, 1);

lcd.print(voltage, 2);

lcd.print(" Volts");
}

but there is fault avrdude: ser_open(): can’t open device “\.\COM3”: Cant be found indicated file …
Help

You need to select the port of your Arduino from the Tools > Port menu.

Thanks

And I have only on port when connected usb cabel ... and doesnt work ..

OK, when you've figured out what "doesnt work" means, get back to us.