Instructions

Game and Knowledge in Electronics-Lab
36
When you open the fridge, the light inside
is on. But what is going on when the door is
closed? It is quite difficult to determine if the
light is off in this case, because you need to
open the door to check it. But for such tricky
situations, there is a little helper, which can
also be locked inside a fridge. The micro-
controller needs the light sensor and the
loudspeaker. The corresponding programme
started with the wire connections A-D and F-G.
If light shines onto the sensor, there will be
sound. But when it is dark, the device will be
quiet. So, put your micro-controller inside the
fridge and close the door. If there’s silence, you
know that the light really is off.
This device can also be used to check the
fridge. Is someone making
a secret trip to the fridge?
He will get a mighty scare
when he opens the door!
Touch a coin with the two naked ends of
your test cables. All six LEDs light up and
indicate that the metal of the coin is a
very good conductor. Try the same with a
rubber eraser and you will see that rubber
doesn’t conduct electricity. All LEDs remain
off. Touch both ends with your fingers. The
result can be very different. If your skin is
very dry, the LEDs will not light up. If there
is a little bit of moisture, up to three LEDs
might light up. You can increase the con-
ductivity by making your fingers wet.
You can now test everything you can find.
Interesting test objects are a pencil lead,
an apple, a potato, tap water, salt water,
dry and wet compost. But you can also
investigate components and devices. Test
the potentiometer and turn the knob while
doing so, or test the tricolour LED between
the different connectors and in different
directions. With a bit of practice you can
even test completely different components
and determine, for example, if a light bulb
is still working or not.
35
Light inside the fridge?
MS
MS
PROG