How to light the heartbeat LED?
Addition for the wiki, it took me a while to find out myself.
The heartbeat LED can be controlled from the daughter board. It is connected to pin 8.
Sample Arduino code:
#define HEARTBEAT (8) // inverted! digitalWrite(HEARTBEAT, LOW); // switch light on delay(2000) // wait 2 secs digitalWrite(HEARTBEAT, HIGH); // switch light off