Sensors ..................................................................................................
Sensorstake energy in forms such as sound or light and transform that
energy into a signal. By using a sensor, you can detect heat, light, and sound,
for example. When a signal is sensed, to the sensor produces an electrical
signal that is used by your circuit to control some activity. For example, an
infrared detector can work in conjunction with an infrared remote control
device to stop or start a little go-kart.Here are a few types of sensors that we use in the projects in this book:IR detector:This converts infrared (IR) light into an electric signal. The
version that we use in Chapters 11 and 9 contains a photodiode that
detects infrared light and an integrated circuit that produces either +V
or 0 volts on its output pin. In order to reduce noise from ambient IR
light, this detector is designed to only respond to IR light that is pulsed
at 38 kHz.Tilt/vibration sensor:This type of sensor (which we use in Chapter 14)
detects motion or vibrations when the switch is mounted with the body
of the sensor horizontal. When the sensor detects motion, it closes a
switch, just like a toggle switch works.Microphones .........................................................................................
Technically speaking, a microphone is a kind of sensor. However, there’s a lot
to say about these sound-sensing devices, so we give microphones their own
section (because we’re the authors, and we can!).How condenser (capacitor) microphones work
Capacitors are kind of like a voltage sandwich in that they have two plates,
with a slab of voltage between them. A so-called condenser mike(also called a
capacitor microphone) contains one plate made of a very light material that
acts as a diaphragm. This plate vibrates when sound waves hit it. This moves
the two plates apart, which changes capacitance(the ability to store elec-
trons). Moving the plates farther apart decreases capacitance (discharging
current), and moving them together increases capacitance (charging current).Condenser microphones aren’t cheap, but they give high-quality sound, so
they are often the best choice for an audio-intensive project.A better mousetrap: Electret capacitor microphones
Today, the most popular type of condenser microphone is the electretmicro-
phone (which gets its name from the combination of electrostatic and magnet),48 Part I: Project Prep