Title:
TELEVISION INTERPHONE SYSTEM
Document Type and Number:
Japanese Patent JPH0235888
Kind Code:
A
Abstract:
PURPOSE:To obtain a guide when a signal line is provided by operating a test switch provided inside a master machine when an interphone system is provided, and issueing an alarm when a current value supplied from the master device to a slave device is <= the prescribed value. CONSTITUTION:When the signal line of the interphone system is provided, the constant current at a high level is sent through a balun 15 and a terminal T1 to a transmission line l by the operation of a test switch SW. The returned current from the slave device 2 side is grounded through a terminal T2, the balun 15 and a resistance RT. That is, the current returned from the master device 1 and the slave device 2 is converted to a voltage at both ends of the resistance RT, and the voltage is compared with a reference voltage VREF by a comparator CMP of a monitor circuit 12. When the voltage at both ends of the resistance RT is lower than the reference voltage VREF, a transistor Q4 of an alarm circuit 13 is driven, conducted through a resistance R5 to a light emitting diode L, and displayed by lighting up a lamp.
Inventors:
MIZUGUCHI KEIICHI
TANIGAWA YOSHIHIRO
UENO YOSHIAKI
TANIGAWA YOSHIHIRO
UENO YOSHIAKI
Application Number:
JP18634388A
Publication Date:
February 06, 1990
Filing Date:
July 26, 1988
Export Citation:
Assignee:
MATSUSHITA ELECTRIC WORKS LTD
International Classes:
H04N7/18; H04M9/00; H04Q9/00; (IPC1-7): H04M9/00; H04N7/18; H04Q9/00
Attorney, Agent or Firm:
Hiroyuki Nakai
Next Patent: JPH0235889