Automatic muting tv when phone rings and display incoming call in lcd display

Discussion in 'The Projects Forum' started by ronald_ng, Jun 2, 2008.

  1. ronald_ng

    Thread Starter New Member

    Jun 2, 2008

    I am doing a project on automatic muting tv when phone rings and display the incoming call in lcd. The line voltage condition is 50.1V without ringing and 53V to 55V when receive ring signal. The frequency for the line is approximately 20Hz. Anyone can give me any relevant information or circuit diagram which i can apply in Malaysia for the above condition? Urgent!!! :confused:
  2. mik3

    Senior Member

    Feb 4, 2008
    You can sue a microphone to detect the ringing tone of the phone or you can use a half wave rectifier and a low pass filter to obtain a dc output. Then divide this dc voltage by using resistors (voltage divider network) and then detect it with your control element (transistor, microcontroller etc). If you use a microcontroller put clamping diodes in parallel with capacitors (zener diodes) to absorb any voltage spikes which can destroy your microcontroller.

    Be aware of the voltage. 50 volts are approximately the limit that the human body will shocked.
  3. Externet

    AAC Fanatic!

    Nov 29, 2005
    You probably measured the line wrong, with a DC voltmeter.
    The ringing signal is about 90VRMS at 20HZ superimposed to the 50VDC.

    As you want the action to take place at ringing, not at lifting handset, you need to use an optocoupler connected to the line trough a capacitor in series. 0.1uF should be enough.
    The ringing signal will pass trough the capacitor and activate the optocoupler to enable the mute condition.

    Your rationale may have a flaw. When the telephone stops ringing because you answer, the tv will go back to audio.

    The convenient way to do it is by sensing the seized line condition and mute the tv during that condition.
    Displaying the caller number is "caller identification" and should be an available service in your country to work. Dedicated gadgets do that.