[henpa]

Yeah, I'm no electronics expert (far from it), but that part also confused me. Can someone explain?

[jonathonf]

Depending on the supply requirements, he might use voltage ripple as a reference.

With an unsmoothed rectified supply you get a nice "pulsed" input anyway:

http://falstad.com/circuit/#%24+1+5.0E-6+1.8479586061009856+...

[smoyer]

True but you'd expect that to be 120Hz rather than 60Hz.

[dogma1138]

Use a diode so you only get half of the sin waves, that's 60hz which makes it very easy to build a clock off since you don't need to do any multiplications on the base clock frequency it self.

[jonathonf]

So you could: a) use a half-rectified supply b) halve the count.

A) would be easier. :)

[smoyer]

True ... not so good for efficiency and you'd need a bigger smoothing capacitor. (I'm assuming since this is all discrete, there's no need for a fully regulated power supply).

[morcheeba]

You'd want a fully regulated power supply for this, /especially/ because it's discrete. You want the LEDs to remain constant brightness, but, more importantly, you don't want an unregulated power supply to overvolt and destroy all this hard work.