LOCAL TELEPHONE LINE WITH DIVERTING SWITCH CIRCUIT SCHEMATIC DIAGRAM

LOCAL TELEPHONE LINE WITH DIVERTING SWITCH CIRCUIT SCHEMATIC DIAGRAM
In normal state, telephone no.1 and telephone no.2 can be used as an intercom when telephone no.3 is connected with the phone cable. To be used as an intercom, pick up telephone no.1 and push switch S1, then piezo buzzer 2 will sound, and so on.

Components :
Resistor R1 : 4.7k ohm
Polar capacitor C1 : 2.2uF/100V
PZ1-PZ3 : Piezo buzzer
S1-S2 : Push button
S3 : ON/OFF stereo switch
12V DC/200 mA power supply

HEADPHONE CIRCUIT FOR FIXED TELEPHONE LINE SCHEMATIC DIAGRAM

HEADPHONE CIRCUIT FOR FIXED TELEPHONE LINE SCHEMATIC DIAGRAM
This circuit requires low power, therefore can be installed parallel with the telephone. Transistor T1, Resistor R2,R3, and Zener diode are used to lower the input voltage become 5V. Transistor T2, resistor R6,R7, and capacitor C5 are used as the sound amplifier. This circuit is equipped with condenser microphone to speak and earphone to hear.