Easy Loudspeaker Circuit For Telephone


This below circuit is a
easy handsfree telephone receiver system. This doesn’t have dialing
circuit so, it’s not a total phone replacement circuit, but it’s just
only a loudspeaker system (i.e, phone receiver,not dialer). This is a
easy circuit with all parts easily available, and without any complex
I.C. It is made of just capacitors, diodes, resistors, and transistors.
This circuit can be made within 70 rupees and it compromises of the
following sections,

Circuit

Circuit diagram

  1. Power rectifier and filter section
    This section is made of a simple bridge rectifier and a indicating power LED.
  2. Voltage regulator section
    This section is made upon transistor Sl100, which is a general purpose NPN transistor in metal package. That is used to regulate voltage at a level of 9+0.6=9.6V by a 9V zener diode.
  3. Speaker output section
    This section contains a high impedance speaker and two BC548 NPN
    transistor to amplify the signal from line, the input of the 548
    transistor pair is fed with a linear or pot control of 10K for volume
    adjust.
  4. Microphone input section
    This section contains a condenser microphone (tablet) and two BC548 NPN
    transistor to amplify the signal from mic, the output of the 548
    transistor pair is fed with a linear or pot control of 10K for volume
    adjust to the line.

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