What would be a good way to open and close an air vent? I have a servo from an old RC airplane that would do the job, but I am hoping to use a less expensive device if possible.
The air vent opening would be a tube of about 10cm in diameter. Somehow I need to open and close a vent with the Arduino controlling it. When closed it should be insulated (hot/cold insulation not electrically isolated). It could be mounted on a flat wall or surface. I was thinking of a piece of styrofoam with a hinge along the top, which would swing up to open the vent and fall down to close it. There would not be a lot of pressure on the vent. I would expect the vent to open and close about 100 times a day.
I can picture how to do it with the servo I have, but is there any other way that could be done with less expensive equipment? Maybe a small motor or solenoid? Maybe in combination with a latch so the solenoid did not have to be powered the entire time? Step motor? Eventually I would hope to run it off of a solar powered battery, so low amp draw devices would be good. Durability is important, it should be able to run at least a year or more, hopefully.
The project is to build a refrigerator that is cooled by outside air during the winter. There will also be a fan and thermistors to measure when outside air is cool enough to chill the fridge, and to turn the fan on and off to adjust the fridge temperature. The air vent "valve" is not strictly necessary, but when the furnace and hot water heater are running in the house, they produce a vacuum that will pull cold air in, which potentially could freeze the stuff in the fridge (not good).