Relay An electrically operated switch, for example a 9V battery circuit connected to the coil can switch an AC mains circuit. The rectangle represents the coil. NO = Normally Open, COM = Common, NC = Normally Closed.
Logic gates process signals which represent true (1, high, +Vs, on) or false (0, low, 0V, off). For more information please see the page on logic gates. There are two sets of symbols: traditional and IEC (International Electrotechnical Commission).
An AND gate can have two or more inputs. The output of an AND gate is true when all its inputs are true.
An OR gate can have two or more inputs. The output of an OR gate is true when at least one of its inputs is true.