We turn On the lights in our washroom when
we enter it and turn them off when we leave.
We sometimes forget to turn Off the lights
after leaving the washroom. This may lead to
power wastage and also the lifetime of the
lights may decrease. To avoid these
problems, we are going to make a circuit
which automatically turns On the lights when
a person enters the washroom and it
automatically turns it Off when he leaves it.

By automating this, there are many
advantages like, the person need not care to
turn On the light always when he is using the
washroom. The circuit which we are doing
does it automatically for that person. Also,
the person need not turn it off after using the
washroom. There is no fear that he forgets
to turn it Off. The circuit is also designed to
consume lesser power so that the circuit can
be used in any household or public
washrooms without worrying about the power

Automatic Washroom Light
Switch Circuit Diagram:


The operation of the circuit is as follows.
When the door of the washroom is opened
and closed, the circuit turns switches On the
light using a relay. When the door opens and
closes for the second time, the circuit turns
Off the light by turning off the relay.

Read good post on
Automatic Door Bell With Object Detection

The element which is used to detect the
opening and closing of the door is a reed
switch. There are two types of reed switches.
We are using the one which will be closed in
normal state and open when there is a
magnetic field nearby. A reed switch
electrically is just a relay kind of component
but unlike a relay which activates when a coil
voltage is supplied, the reed switch activates
when a magnetic field is detected in the
vicinity. The circuit is given a power supply
of 9V. The pin-16 of IC 4017 is given 9V. The
pin-8 of 4017 is given to ground.

The circuit uses IC 741 op-amp as a
comparator arranged such that its output is
high by default when the door is closed. The
circuit is attached to the door frame whereas
a permanent magnet is attached to the door
in such a way that it comes closer to the
reed switch when it is closed. The IC 4017 is
made to alternate between each door open
and door close. When the door is opened and
closed for one time, the circuit turns On the
relay and the the Light turns ON. When the
door is opened and closed for the next time,
the circuit turns Off the relay and the light
turns off. The IC 4017 is capable of counting
upto nine counts but we are restricting it to
count only two and reset back. The ability of
this IC to adjust the count value as desired
helped us in this project to use it as a one
bit counter.

When the door is closed, the reed switch
opens and hence the op-amp output which is
the 6th pin of IC 741 is HIGH. When the door
is closed, the pin-6 of IC 741 is turned Off.
When the door is closed back, it triggers the
IC 4017 decade counter and hence the relay
toggles ON and OFF for each door open and
close operation.

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