Hi Guys,
I'm totally new here and just starting to do some reading. I'm interested in building a rig like this:
BUT it can use a much smaller solenoid and the entire setup needs to be battery powered. Does this seem feasible with a smaller than 12v battery? Or will the components drain the battery too quickly (even when not in use, but bluetooth needs to remain on). Any help or advice is appreciated, my electrical knowledge is minimal, and most of the arduino boards seem to require a 12v supply.
I would suggest that you build the circuit exactly the same as the Make example. If you have a multimeter with a miliamps scale, then measure the current consumption of the circuit. Then calculate how big of a battery you need to meet your intended battery life. (You didn't tell us how long you want this to run on a battery - days or years?)
Remember the 'size' of a battery is not measured by its voltage. I've seen 1.2v batteries that require a crane to lift them. The important rating is the amp-hours or, for most batteries, the miliamp-hours (mAh). A 1000mAh battery will provide 5mA to a circuit for 200 hours, for example.
Arduino is not built for low power consumption. You can run the smaller ones off a coin cell but they still aren't intended to run for months or years in the same way that your car-key remote does. Getting that sort of battery life requires more than just a basic Arduino.