This circuit can be used to glow a bulb or turn a alarm when the phone rings.Using this circuit  nuissence of telephone ring at night can be avoided.

When the telephone rings the line voltage rises to 72 volts.At this time the LED in the opto-coupler glows and the transistor conducts. Due to this the transistor Q1 conducts.This makes the relay ON.The load connected to the relay whether bulb or bell turns ON.


Circuit diagram with Parts list. 




  • Assemble the circuit diagram on a good quality PCB or common board.
  • Use a 5V DC power supply for powering the circuit.
  • The load can be connected through NC1,NC2 & C points of the relay.


  1. Seetharaman

    Hi Edgardo use it as a zener not as a diode.

  2. Hi Seetharaman,
    Thank you for the reply,
    With your assessment of the circuit, what circuit will I follow, the cathode to anode connection or the reversed zener connection.
    I am going to solder all the components but waiting for your reply to make GO of my project as featured.
    Thanks again.

  3. seetharaman

    Hi Elgardo it looks like both the zeners are reversed. When AC appears positive going will conduct above 40 volt and hence the LED in opto coupler will conduct in the negative cycle the zener and diode will conduct at low voltage itself hence no signal through optocoupler. With the peresent configuration relay will chatter always.

  4. Hi,
    This is a good circuit for my plan to amplify the telephone ringer in our factory’s production area.
    My question is;
    Are the zener diodes connections correct?
    I have seen like this circuit from Aaron cake but the connection of the zener diodes are in cathodes.
    Or these connections both will work?
    Thanks in advance.

  5. i AM a student in 12.
    are the circuit diagrams of buying sites are true ? or having some missed parts
    this opinion came in my brain becozzzz
    i hav downloaded a circuit diagram from” buying site” (name i don’t knew) but there is some problem in the circuit that don’t work
    even i met the specialist also
    diagram was of “automatic street signal” based on ‘LDR’