eli5: how do cctv cameras work?


How do cameras transport visual information to a different location with just a couple of wires?

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An optical sensor takes an image and converts it into digital information. That digital information is set down the wire. Once the display unit recieves the digital informaiton, it recreates the image

In addition, it’s a closed circuit network of cameras. So each camera at their own position will have varying timeframes for recording.

Most often it’s 24/7 with monitoring from security. However there are two types, on site and off site monitoring and recording.

Onsite is seen most often with smaller companies. Mom and pop shops, however larger companies have it as well.

Off site monitoring can be done by larger companies that outsource the work for multiple reasons. Possibly insurance claims if there is any claims like damage from weather, people, animals etc, or thefts. There is a separate eye witness for legal reasons and the equipment is installed and maintained by that company. Like ADT, or even Brinks security. But most importantly the video feed can be left with the company off site safe and secure to an extent.

> How do cameras transport visual information to a different location with just a couple of wires

How do you think tv or the internet works?

Everything is encoded, which means the data is converted into a format for transport and then read by a display to be converted into pixels.

The same way any other TV works.

I’ll use NTSC (American old analog) as an example, because it’s simple. An NTSC video signal is a series of lines. Each line is just the brightness of a meter as it sweeps across the line. When the meter reaches the end, it jumps down to the next line, and the source transmits a very strong pulse (called H-blank).

When the meter reaches the bottom of the screen, the next several lines are filled with “special” data. At minimum, this is just an easily detected pattern (called V-blank) that the receiver can use to jump back to the top.

Color (if supported at all) is transmitted, by adding an oscillating sine wave to the video signal. Technically two (one for red, and one for blue), each staggered a quarter-cycle apart. During each H-blank, a few cycles of solid red are transmitted, so a color receiver can remember its timing and tell the two color signals apart. A monochrome transmitter can omit color altogether, and a monochrome receiver can ignore color.

Importantly, the thing with these kinds of analog TV, is that they are just a stream of voltages over time. So they don’t care if they’re transmitted over the air, or a pair of wires. (You need a minimum 2, since electricity needs a return path.)

Digital is the same, except that instead of the light readings being exact voltages, they’re specific patterns of 1’s and 0’s.

The eye in the camera (ccd sensor) takes the light (image) the camera sees and converts it to a varying voltage on the wire (coax, cat5, etc). The recorder or television takes that varying voltage and remakes the picture with light.