This is an old post, preserved for reference.
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Following on from the previous articles on the LED Clock (a simple replacement and a teardown of the original clock and a more complicated replacement), the parts I ordered from CPC have finally arrived, I've now finished the replacement unit. And here it is.
The pin header on the left pokes out of the side of the clock, where there used to be a slide switch. This allows the 'Arduino USB2Serial light' to plug in to reprogram the unit, or to set the time.