Originally Posted by noelex 77
Rob have you any information of the self consumption of the circuit?
The 555 consumes about 100mW at 12v and overall consumption will be that plus the power usage of the original LED when it's on. In savings from forgetting to manually switch the thing off, you should be well ahead. IOW there's really no reason not to use this circuit unless soldering up a piece of Veroboard (tm) is beyond you.
The chip itself sells for under $0.50 (20 pcs for $7.99, free postage) on eBay. Light dependent resistors are around $0.35 in 10-off quantities.
Fitting it on a vertical surface should obviate the need for cleaning
BTW the load can either go from the Output pin to Ground, or to +12V, depending on whether you need to switch something ON or OFF at night. The Output pin can source or sink 200mA, larger loads can be routed through an additional transistor switch or even a relay.
As far as basic electronic building blocks go, the 555 would have to be one of the most useful ICs ever invented. I'm sure you can think of a few other uses for a timer chip aboard as well. A 20-min wake-up buzzer while single-handing, a shower pump
timer? Wouldn't leave the dock
The 555 book has loads of additional uses listed: http://www.4shared.com/rar/iy3nZYxK/555_book.html