Automatic Timer for Rain Barrel

Since I had a rain barrel I wanted to add a little automation to it. The best time to water is early in the morning, before the sun has come up. of course, early in the morning I need to be off to work. To help me out I purchased an Automatic Water Timer and some soaker hose. After hooking it all up I was quite pleased with myself.
It took me a while to realize it, the automatic timer wasn’t working. It never actually came on. The problem was that I was testing it by hooking it to the house water line then, when it worked fine, I put it back on the barrel. Apparently (obviously now), there are two kinds of automatic timers. The kind that use the high pressure of city water lines to actuate and the kind I need for a gravity fed system.
When you get your own make sure it’s one that operates at 0 PSI, not just the kind that works with low pressure soaker hoses.
I ended up ordering a Solar Rain Barrel Timer online, which says it can operate at 0-80 psi. I couldn't find anything similar in any of my local hardware stores and this one seemed the best for the price.