I built a variant of the compressed air rocket launcher on Make Weekend Projects.

I don’t know who is having more fun with it, me or my kids. OK, I admit I am having more fun, but they love it too.

In any event, after having to repair the sprinkler valve control circuit a couple of times, I sat down to build something more reliable, and this is what I came up with.

Two 9V battery harnesses, two mono jacks from radio shack, and the box from an old ipod.

The case is upcycled from an old ipod box, and the connectors are cheap female mono audio jacks from Radio Shack. Even though valves is spec’d at 24VDC, 18VDC from the two 9V batteries is very reliable for dozens if not hundreds of activations.

The sprinkler valve and the launch release switch get the same treatment, using male audio jacks.

The switch and valve each get an 1/8″ male audio jack, again from Radio Shack

Here is the wiring diagram:

When we’re not launching air rockets, this system also works great for controlling the pneumatic-activated Halloween props I’ve built (more on that in another post).