Instructables

Day/Night sensor with 3hour delay?

Hi!

I need to build a circuit for a friend. He has a billboard that needs to be lighted every night, but it needs to be lighted only for about three hours (until he closes shop). 

The only problem is, there is no way to get mains power to the billboard, so we figured that we'd set a small 12v battery, solar cells, and some led tape, that would be enough. 

Now all i need is a 12v circuit that would detect low-light conditions (night) and would turn on a timer which would turn off the whole circuit after 3 hours.

I searched the net and my local electronics stores, but couldn't find a circuit that would suit my needs... 
So any help would be greatly appreciated!

mpilchfamily8 months ago
So the place closes 3 hours after sunset regardless of the time of year? If not an LDR and 3 hour timer may not be the best option. What's the matter with lighting the sign up and flipping a switch.
Hrenowsky (author)  mpilchfamily8 months ago
The problem is, thah the sign is too far from the store to run any cable to it. Also there's a human factor of forgetting to turn the sign on, or forgetting to turn it off and completely discharing the battery...
Burf8 months ago
It seems to me that you're overthinking the problem. Why not just use a standard light timer with a 12 volt wall wart transformer? Something like this:
timerswitch.png
mpilchfamily Burf8 months ago
He did say there is no way to get mains power to the board.