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Telephone line Based Audio Muting and Light-On Circuit . Very often when enjoying music or watching TV at high audio level, we may not be able to hear a telephone ring and thus miss an important incoming phone call. To overcome this situation, the circuit presented here can be used. The circuit would automatically light a bulb on arrival of a telephone ring and simultaneously mute the music system/TV audio for the duration the telephone handset is off-hook. Lighting of the bulb would not only indicate an incoming call but also help in locating the telephone during darkness. . Telephone line Based Audio Muting and Light-On Circuit diagram :   Telephone line Based Audio Muting and Light-On Circuit Diagram  . On arrival of a ring, or when the handset is off-hook, the inbuilt transistor of IC1 (opto-coupler) conducts and capacitor C1 gets charged and, in turn, transistor T1 gets forward biased. As a result, transistor T1 conducts, causing energisation of relays RL1, RL2, and RL3...

 Build a MT8870 DTMF Telephone Dial Tone Decoder Circuit Diagram. This is a  simple MT8870 DTMF Telephone Dial Tone Decoder Circuit Diagram . In this circuit one common DTMF receiver IC is the Motorola MT8870 that is widely used in electronic communications circuits. The MT8870 isan 18-pin IC. It is used in telephones and a variety of other applications. When a proper output is not obtained in projects using this IC, engineers or technicians need to test this IC separately.  A quick testing of this IC could save a lot of time in research labs and manufacturing industries of communication instruments. Here’s a small and handy tester circuit for the DTMF IC. It can be assembled on a multipurpose PCB with an 18-pin IC base. One can also test the IC on a simple breadboard. For optimum working of telephone equipment, the DTMF receiver must be designed to recognize a valid tone pair greater than 40 ms in duration and to accept successive digit tone-pairs that are greater than ...

Build a Telephone Conversation Recorder Circuit Diagram . This Telephone Conversation Recorder Circuit Diagram enables automatic switching-on of the tape recorder when the handset is lifted. The tape recorder gets switched off when the handset is replaced. The signals are suitably attenuated to a level at which they can be recorded using the ‘MICIN’ socket of the tape recorder. Points X and Y in the circuit are connected to the telephone lines.  Resistors R1 and R2 act as a voltage divider. The voltage appearing across R2 is fed to the ‘MIC-IN’ socket of the tape recorder. The values of R1 and R2 may be changed depending on the input impedance of the tape recorder’s ‘MIC-IN’ terminals. Capacitor C1 is used for blocking the flow of DC. The second part of the circuit controls relay RL1, which is used to switch on/off the tape recorder.   Telephone Conversation Recorder Circuit Diagram A voltage of 48 volts appears across the telephone lines in on-hook condition. This volta...

A project of Telephone for VoIP gate Circuit Diagram. Calls over the Internet can be in several different ways. For households with a permanent connection to the Internet, it is advantageous to use different IP phones and VoIP gateways that need to function on the computer. Because IP phones are still relatively expensive, they are used more often different VoIP gateway. VoIP gateway is "one end" connected to a network with access to the internet, the "other end" connects a standard analog phone, which is then used in the normal way and that has given a telephone number available from any fixed or mobile phone. Some VoIP gateway router in addition to that we need as well, if we want to access via a modem to connect multiple computers. To my VoIP gateway, we can connect nehomologovaný, self made ​​phone. Instructions for simple phone is the subject of this article. How to the phone works Normally the phone line is a DC voltage, usually 50 to 70 V. During the ring...