JPS6280459U - - Google Patents

Description

【図面の簡単な説明】[Brief explanation of the drawing]

第１図は本考案の盗聴防止回路の回路図、第２
図は本考案の盗聴防止回路を備えた第１電話機、
第２電話機のブロツク図である。 主な図番の説明、３……通話回路、９……スイ
ツチ回路、１３……送受話回路、１４……電圧検
出回路、２０……パルス幅識別回路、２１……ラ
ツチ回路、２２……ラツチ解除回路。 Figure 1 is a circuit diagram of the wiretapping prevention circuit of the present invention, Figure 2
The figure shows the first telephone equipped with the wiretapping prevention circuit of the present invention.
FIG. 3 is a block diagram of a second telephone. Explanation of main drawing numbers, 3 ...Telephone circuit, 9 ...Switch circuit, 13 ...Talking/receiving circuit, 14 ...Voltage detection circuit, 20...Pulse width identification circuit, 21...Latch circuit, 22... Latch release circuit.

Claims (1)

【実用新案登録請求の範囲】[Scope of utility model registration request] 同一回線に並列接続される共同電話機において
電話回線の電圧を検出する電圧検出回路と、前記
電圧検出回路の検出信号を一定期間識別して該検
出信号に対応する識別信号を出力するパルス幅識
別回路と、電話回線がオフフツク状態の時に前記
パルス幅識別回路の識別信号によりラツチ信号を
出力するラツチ回路と、該ラツチ回路のラツチ信
号により通話回路を制御するスイツチング回路と
前記パルス幅識別回路よりの所定の識別信号又は
、スイツチング回路を介しての通話回路の電圧が
所定電圧の時にラツチ回路の動作を解除するラツ
チ解除回路とよりなり電話回線をオフフツク状態
にさせた電話機は瞬時に、通話回路の電圧により
ラツチ解除を起させて通話回路の動作を維持し、
他の電話機ではラツチ回路の起動により通話回路
を不動作にさせることにより盗聴防止を行なうこ
とを特徴とする盗聴防止回路。 A voltage detection circuit that detects the voltage of a telephone line in communal telephones connected in parallel to the same line, and a pulse width identification circuit that identifies a detection signal of the voltage detection circuit for a certain period of time and outputs an identification signal corresponding to the detection signal. a latch circuit that outputs a latch signal based on the identification signal of the pulse width identification circuit when the telephone line is in an off-hook state; a switching circuit that controls a telephone call circuit using the latch signal of the latch circuit; and a predetermined signal from the pulse width identification circuit. The identification signal or the latch release circuit that releases the operation of the latch circuit when the voltage of the communication circuit via the switching circuit reaches a predetermined voltage causes the phone to put the telephone line in an off-hook state, and the telephone instantly changes the voltage of the communication circuit. causes the latch to be released and maintains the operation of the communication circuit,
A wiretapping prevention circuit that prevents wiretapping by disabling a communication circuit in other telephones by activating a latch circuit.