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I have been working on a setup for a sound installation, and have hit a bit of a wall trying to figure out the best solution for automatically turning the installation on for a few hours a day.  Originally I was using a simple circuit with a photocell, transistor and H1AA005 relay but the lighting situation at the site is not consistent enough for this to be a viable solution.  I also would prefer to limit the # of hours the installation is on per day to save the battery (with the photocell solution, if it was consistent, the installation would be on 12+ hours a day, but with a timer I would probably put it on for 5 or less). The installation will be up for 6 weeks, and the timer will be set once and will not be altered for the duration of the installation. It must run off a 12v battery. I am wondering if anyone is familiar with a simple and inexpensive solution (either using Arduino or not)? In my initial research the solutions I've come across are either very expensive (more than $100) or very involved.  Many thanks for any input or links!  A detailed diagram of the system (including load requirements, etc.) is attached.

[Reply #1 on:]

http://prostores1.carrierzone.com/servlet/super-feed_com/-strse-5/12-volt-dc-programmable/Detail

FYI this is the most promising ready-made solution I found.  It's a bit pricier than I'd like but it's definitely the cheapest option that I've come across which does what I need. 

[Reply #2 on:]

Indeed, using an arduino with a RTC (realtime clock) module would be your cheapest option (< 30 euro /dollar). Gives you more freedom as wel.

Just calculate the periods you want your device in terms of seconds since 1-1-1970 and have your code poll every minute orso whether such a period is begun. You do need to power the arduino of course. But maybe you can do that from the solar source?

a tut: http://www.ladyada.net/learn/breakoutplus/ds1307rtc.html on to build your own

but you can also get these module preassembled http://www.sparkfun.com/products/99

[Reply #3 on:]

Thanks, that's very helpful--much appreciated!