Here is my First published Instructable - an poor man's efficient AUTO DOOR Closer which is totally gravity driven

Step 1: Automatic Door Closer - Materials

1. 2 meter long rope (preferably nylon - 5mm or thicker than that)

2. 1 wood screw or nail - atleast 2 inch long

3. empty 2 liter soda bottle

4. water(or sand) - as per requirement

Tools

5. Screw driver or Hammer

Step 2: How It Is Made?

1. Start with driving the screw in the top limp of the frame of the door.

It should in the center or towards the opening side but not close to the hinge.

Drive the screw or nail deep enough to carry at most 2 kg of weight( which depends on the speed of closure needed).

2. Tie the rope one end to the pet bottle and the other end to the nail securely. the rope length should be so that the bottle hangs at the center of the door or lower. (So by Indian standards for a 2 m high door take 1 m long piece rope.)

3 . Next fill the bottle with water or sand as you wish. But the level of material depends mainly on the speed at which door need to be closed and also changes with the weight of the door. But when the door closes fast it gives a bigger unpleasant bang noise. It can be avoided by properly sticking some foam or thermocole without affecting the full shutting of door. But it is to the user to decide. I didn't use any foam, rather I used lesser water in the bottle.

4. This method saves a lot of walking to open or closing the door as the case may be in any room or home. Also it is helpful in preventing heat to enter as in air conditioned room and vice verse in heated rooms.

5. This is very cheap and effective and operates by gravity. Low maintenance as the rope may wear out after continuous rubbing with door. If improved, a pulley placed at the rubbing point will improve the functioning.