Specifications

CIRCUIT IDEAS
tive half cycles and off-period of ring sig-
nal. Once the handset is picked up, the
relays will still remain energised because
of low-impedance DC path available (via
cradle switch and handset) for the in-built
diode of IC1. After completion of call when
handset is placed back on its cradle, the
low-impedance path through handset is
no more available and thus relays RL1
through RL3 are deactivated.
As shown in the figure, the energised
relay RL1 switches on the light, while
energisation of relay RL2 causes the path
of TV speaker lead to be opened. (For
dual-speaker TV, replace relay RL2 with
a DPDT relay of 6V, 200 ohm.) Similarly,
energisation of DPDT relay RL3 opens
the leads going to the speakers and thus
mutes both audio speakers. Use ‘NC’ con-
tacts of relay RL3 in series with speakers
of music system and ‘NC’ contacts of RL2
in series with TV speaker. Use ‘NO’ con-
tact of relay RL1 in series with a bulb to
get the visual indication.
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