I have been trying to work on this myself but not very successfully, as I haven't done much of this before.
I need a countdown, starting at 500, which is displayed at 1 second intervals. The countdown is never to reach 0; at random intervals, the countdown restarts. The restart is from a random number between 500 and the current number (I need it to be a little less obvious than restarting from 500 each time).
Ideally I would like the numbers to be displayed as seven-segment digits, like on stop watches, and as large as possible.