12V fans and water-pump are either always on or else only on for a few seconds when needed.
- Eyebrow fans ... always on (see attached pic). Subtly move the fiber-optic eyelashes so that Dragon appears to be in a world where there is wind blowing. These are the only ones not controlled by NetDuino.
- Dry-Ice water pump ... on for a few seconds when its time for the Dragon to exhale. Send hot water from large thermos into Dry-Ice compartment.
- Throat fans ... on for a few seconds in sync with water pump. Send the dry-ice fog generated by the hot water out the mouth.
- Nose fan ... on for a few seconds when its time for the Dragon to inhale. Nasal cavity is air-tight compartment about the size of a toaster with large concealed fan blowing air out. Fan is hidden in the roof of the mouth, which is closed during inhalation. Only air intake path is the two large nostrils, so I expect (not proven yet, but ever hopeful) that the fog will be sucked into the nasal cavity and make it appear that the Dragon is inhaling. At the same time, the yellow lights in the nasal cavity glow brighter and the servos attached to the nose slowly raise it up a few inches.
So ... short answer ... all I need for NetD to do is cause 12V to be turned on for a few seconds and then off again. Don't need to vary the 12 volts. Played with that initially, but found it wasn't really necessary since short on/off bursts do the trick just as well.