If the apartment to one telephone wiring pine in different rooms connected telephone sets, each of them can be equipped a simple indicator of employment telephone line that will allow the "no dig" in others conversation on one of the phones in parallel. In addition, the indicator able to signal the unauthorized use of a telephone line.
Diagram of the device shown in Fig.1.
The indicator is connected in parallel telephone line in accordance with its polarity. To protect the device from wrong connection is suitable diode VD1. When all of the telephone phones, modems, faxes "on the tube", the voltage on the telephone line - about 60 In (30 .40 In some types of PBX). High voltage through current limiting resistors R1, R2 and working in Micropower mode Zener bipolar transistors VT1 VT3 ...goes to the gate of field transistor VT5. Since voltage gate-source VT5 its threshold more voltage opening. VT5 is open and the other transistor (VT7) is closed, and super bright blue led HL1 is not lit. In this mode, the device consumes a current of about 8 mA, which is significantly less than that of the device [1-3].
If one of the parallel phone off the hook, the voltage telephone pine is reduced to 8...20 V, VT5 is closed, VT7 open, and led HL1 lit, signaling employment telephone pine. In this mode one the device draws from the telephone line current: 280 mA. Application super-bright led makes it possible to obtain a sufficiently bright luminescence at low current. Transistors VT4, VT6 limit the maximum voltage gate-source field-effect transistors at 7...10 V, preventing their breakdown. The Capacitor C1 reduces the sensitivity of the device to occasional short-term changes the voltage on the telephone line.
The device is mounted on a printed circuit Board size 35x35 mm (Fig.2). The printed circuit Board of this size easily fits in standard European wall socket on two telephones.
Bipolar transistors CTG you can replace any of the series CT. KT315. CT, SS9014. Field-effect transistor CPA can be replaced by CPA. having the same Pinout or BSS88. CPA, CPB. ZVN2120. Transistor VT7 (CPA). can withstand voltage the source-drain 400, you can replace imported analogue BSS124 or (with lower the reliability of the device) on CPA. KPA. given the differences in sokolivka. Super-bright led RL50-CB744D blue color and brightness of about 6000 MCD when the direct current of 20 mA can be replaced by DB5b-448ABCA (3000 MCD. blue), DB5D-448ABD (3500 MCD, blue), DB5-435SOR (4000 MCD, red), DB5-133AGCA (7000 MCD. green) and other similar. Diode KD243ZH can be replaced by any of the series CD,1N4003...1N4007.The condenser is any compact ceramic, resistors-C1-4, or imported counterparts. You can apply the SMD components.
The finished device does not require networking. On one telephone line can to set up to 8 of these indicators. When the device is placed inside the phone its connection is desirable to do so. so when you pick up the handset on this device is the power indicator is disconnected from the telephone line.
Literature
Author: A. Butov, S. CORBA Yaroslavl region