In the history of television, there are a handful of events that stand out. The invention of black and white tv sets, the first broadcasts of television signals, the color tv, and the rise of cable television sets stand out in particular. Additionally, the VCR marks an important event in the history of TV. For the first time, people could control what they wanted to watch on their tv sets. Video stores, something that was non-existent before, started popping up on nearly every street corner. The other amazing thing about VCR sets is how they work. Find out how these incredibly intricate and interesting devices work.
The VHS Tape
For a device that you can buy for $2, the VHS is pretty complex. Comprising of an outer shell with a moving, spring-loaded door, the main part of the VHS is the tape. Two spools hold the tape while two spring-loaded locks prevent the tape from unrolling, and low-friction rollers guide the tape across the front of the shell. The tape itself is 800 feet long and 1/2 inch wide. It is oxide-coated mylar tape and it acts as the recording medium. When the tape is inserted into the VCR, the VCR uses a lever to release and open the door. This exposes the tape and inserts a pin into the hole to disengage the two locks on the spools. Then the drive can extract the tape and play it.
The VCR has two main jobs; to deal with the fragile and incredibly long tape, and to read the signals off the tape and convert them into signals that a TV can understand. The recording heads are mounted on a rotating drum that is tilted in respect to the tape. The device has to read the audio and control tracks from the tape, keep the tape moving at exactly the right speed and detect the end of the tape. When a VCR loads the tape, two rollers pull the tape out of the cassette. The rollers help move the tracks around the drum. Then the pinch and inertia rollers engage and the tape is pressed onto the erase and audio heads. To sense the end of the tape, the VCR shines a light through the tape and when it “sees” the clear leader, it knows the end of the tape.