McBain wrote:When I plug in the Uno, the on/off LED turns on, and the pin 13 LED begins flashing steadily at about .5Hz. When I attempt to upload a sketch, pin 13 blinks very rapidly at the moment I click upload, then returns to blinking steadily at about .5Hz.
I realize this is a long shot, but the .5hz blinking of the LED is the demo program "Blink" loaded into the Arduino when it was originally programmed with a boot loader. It provides a quick visual check that the AVR is working.
Sometimes, the first "demo" program people attempt to upload is also "Blink.pde" which is effectively the same program.
If you were trying to upload blink.pde you would get the symptoms you describe, .5 hz blink, rapid blinking, .5hz blink. I suggest to folks who are trying out the Arduino for the first time that they change blink.pde to either blink quickly or very slowly. That way the blink rate changes from the original install