What is CCTV ? CCTV is ( Closed-circuit television ) also known as video surveillance, is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. Why use ? Mainly surveillance
What is Relay in Electronics ? A relay is an electromagnetic switch operated by a small electric current that can turn on or off a much larger electric current.Relays was invented in 1835 by American electromagnetism pioneer Joseph Henry in