The first garage door opener consisted of a radio transmitter, a receiver and an actuator to open or close the door. In this the receiver would detect a change in the amplitude and would open or close the door. However there was a security concern with these kinds of garage door openers. They could be opened by anybody with a transmitter. Also there were accidental openings of garage doors by neighbors trying to open their doors. The later door openers used a shared frequency to overcome the accidental opening by other users. Using dipswitches a total of 256 combinations were made to prevent interference from other garage door openers. However the security issue was still not overcome.
The present day garage door openers use rolling frequency or hopping code technology. In these the frequency of opening is look ahead type, that means every time the door is opened then the next time the door will be opened by another frequency.
The technology for garage door openers is fairly simple. Three kinds are used, chain drive, screw drive and belt drive. Chain drives are noisy as they use a metallic chain along with a metal trolley. However they are fairly cheap about $130 Screw drives consists of a threaded lead screw. They start at about $150 The newer models consist of plastic lined tracks to reduce the noise and increase the speed of opening. Belt drives are the costliest and the quietest. They begin at about $170
There is a misconception that the lifting is done by the door opener. However the actual lifting is done by the springs. When the door is closed the springs come into tension. When the door is being opened the spring does most of the lifting. There are two types linear expansion springs and torsional springs. Garage door openers are of two types, jackshaft type and trolley type. The jackshaft type occupies less space. The trolley type consists of trolley attached to the door and also to the motor. This occupies space in the ceiling but is more popular because it is safer. In jackshaft type, it is difficult to sense when someone is being crushed under the door. There are two types of motors available, AC and DC. AC is more common but DC has many advantages. It consumes less electricity, the speed is easily controlled and makes less noise.
There are some models which auto reverse incase of obstruction like a pet or a child. The remotes usually operate up to a distance of 150 feet. The remote can be used to switch on the light of the garage also. Most garage door openers come with a keypad, which can be installed outside the garage. This is used to open the garage, if the remote batteries are down or the user has forgotten the remote. Most garage door openers allow emergency release so that the door can be opened manually in case of power failures.
