Article : Andy Collinson
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.
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 electro-mechanical counter in parallel with the lamp. This registered each
time someone pressed the switch....in fact, I can remember a time when I had more "hits"
on my doorbell counter then at my web site :)