Arduino board LED and external LED on pin 13 blinking at different rates

Trying the blink example code without any modification on a Duemilanove board (with ATMEGA328) I get the board LED blinking correctly every 1000ms and the LED connected to pin13 blinking almost three times during the on cycle of the board led...

Any ideas why and how to fix it?

It might be a flashing LED - some LEDs have a chip inside them that makes them flash. Does it flash when connected to +5v? (use a series resistor for this test - even though if it is a flashing LED it probably won't need one)

gosh.. you're right! I didn't know about different kinds of LEDs. It's a flashing one, mystery solved.

thanks for the quick reply

Wow.. I was ALMOST ready to say "That's Impossible".. but I have learned the hard way NOT to say that :slight_smile:

I ALMOST wish you hadn't answered this already...

It ranks up there with the unknown, hidden from view, left-handed threaded access screw.