Hardware Reference
In-Depth Information
Figure 6-7
This intervalometer was built using
the same methods as shown above.
An Arduino in the box senses a
change from the PIR sensor and
sends an IR signal to the camera to
take a picture.
A
A.
PIR sensor
How Radio Works
Radio relies on the electrical property called
induction
. Any time you vary the electrical
current in a wire, you generate a corresponding magnetic field that emanates from the
wire. This changing magnetic field induces an electrical current in any other wires in the
field. The frequency of the magnetic field is the same as the frequency of the current
in the original wire. This means that if you want to send a signal without a wire, you can
generate a changing current in one wire at a given frequency, and attach a circuit to the
second wire to detect current changes at that frequency. That's how radio works.
The distance that you can transmit a radio signal depends
on the signal strength, the sensitivity of the receiver, the
nature of the antennas, and any obstacles that block the
signal. The stronger the original current and the more
sensitive the receiver, the farther apart the sender and
receiver can be. The two wires act as antennas. Any
conductor can be an antenna, but some work better than
others. The length and shape of the antenna and the
frequency of the signal all affect transmission. Antenna
design is a whole field of study on its own, so I can't do it
justice here, but a rough rule of thumb for a straight wire
antenna is as follows:
Antenna length =
5,616 in. / frequency in MHz =
14,266.06 cm. / frequency in MHz
For more information, consult the technical specifications
for the specific radios you're using. Instructions on making
a good antenna are common in a radio's documentation.
Radio Transmission: Digital and Analog
As with everything else in the microcontroller world, it's
important to distinguish between digital and analog radio
transmission. Analog radios simply take an analog electri-
cal signal, such as an audio signal, and superimpose it
