H04Q1/00—Details of selecting apparatus or arrangements
H04Q1/18—Electrical details
H04Q1/30—Signalling arrangements; Manipulation of signalling currents
H04Q1/38—Signalling arrangements; Manipulation of signalling currents using combinations of direct currents of different amplitudes or polarities over line conductors or combination of line conductors
Landscapes
Engineering & Computer Science
(AREA)
Computer Networks & Wireless Communication
(AREA)
Relay Circuits
(AREA)
Charge And Discharge Circuits For Batteries Or The Like
(AREA)