Circuit Project: Doorbell Warning Switch


This circuit will light a
lamp at a remote location when the doorbell switch is pressed. This
circuit should only be used with the solenoid type doorbells, the
electronic type that play tunes will not work here. It is quite easy to
miss the sound of a doorbell if you are watching TV , this circuit gets
round the problem by providing a visual indication. As an alternative, a
LED could also be used. You could just
parallel a lamp across the doorbell, but this would mean extra drain
from the doorbell batteries or transformer.

Circuit

Circuit diagram

A series resistor, R1 is wired in series with the doorbell and
reduces current flow, thereby increasing battery life. The value of R1
is chosen so that about 0.6 to 0.7 volts is developed across it, when
the doorbell switch is pressed. I used a combination of a 22 ohm
resistor in parallel with a 50 ohm. The voltage drop across R1 is
sufficient to switch on the transistor, the lamp in series with the
collector will then illuminate. I also used an electromechanical counter
in parallel with the lamp.


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