Phone rang indicator light Electronic Circuit

From CircuitsArchive

This, will detect the ring signal, energize the relay which latches up, and the LED comes on and stays on till you push SW.

                                                 ____
 tip o--CC---RR----o-D<-------o-----o------>D----^  ^----o-----+
                   |          |     |             SW     |     |
                   |          |     |                    |     |
                  \-/         |-    R||                  B-    LED
                   Z          C     L|| ............     A     |
                   |          |+    Y||          __.__   T+    R
                   |          |     |         +--o   o---+     |
                   |          |     |         |                |
 ring o------------o----------o-----o---------o----------------+
    
    CC=.47 uF 200 V. capacitor
    RR= 3k (depends on relay)
    D = 200V diode  ( > < direction od diodes)
    Z = 12 zener
    RLY= any small relay
    SW= normally closed switch
    K = relay's contacts
    BAT= 9 V. battery
    R = 500 ohm (for LED)
    C = some (10) uF capacitor
 

Components are not critical. It should latch on first ring, if not reduce RR. If it took too long to deenergize, reduce the C.

Sources

• Massoud Ajami (massoud[at]chemteca.sdsu.edu)