Sometimes you just need an extra minute to prepare for a
guest’s arrival. When the doorbell
rings, it’s often too late. Why not
install an infrared photoelectric system that will alert you to the presence of
a guest before they ever make it to your door?
Infrared photoelectric sensors may be used to detect objects
in a number of ways. Mounting the sender
and the receiver across from each other is known as a through-beam
configuration and provides the strongest beam.
Retro-reflective mounting places the sender and the receiver on the same
side and bounces the infrared beam off an object when it is in close enough
proximity. Diffuse proximity mounting
uses the same layout as retro reflective, but also uses a reflector on the side
opposite the photo eyes. Any of these
three configurations may be used to set up a driveway monitoring system
depending on what type of structures are adjacent to the driveway.
Evaluate the best location to mount the sensors. This may be a mailbox, a fence post, a brick
building, a bridge, or whatever standing structure happens to be within range of
the driveway. If you mount the
photoelectric sensors in a through-beam configuration they do not need to be
very close to the driveway, whereas the other two options will need to be much
closer, depending on the type of photoelectric sensors used, like ten to
fifteen feet.
Trace a route back to your home for burying the sensor wires,
but don’t put the wires in the ground yet.
Instead, extend the wires back to the house above-the-ground and connect
the photo eyes to the appropriate power source or to an external amplifier if
the photoelectric system includes one.
Connect the output of the sensors to a buzzer or bell with a noise that
is distinctly different from the sound that your doorbell or telephone makes so
that you can easily distinguish them.
Many photoelectric amplifiers include a relay output, so connecting them
to a buzzer should be as easy as connecting a mechanical switch. See the manufacturer’s website for wiring
diagrams.
Test the system using different types of cars and trucks and
also people. Adjust the sensitivity of
the photoelectric system to the optimum level and mount the photo eyes at the
right height from the ground to hit the midsection of most vehicles. When everything is set correctly, bury the
conduit containing the wires and do your best to conceal the photo eyes from
view. This system will provide a
reliable means for detecting guests before they are standing on your doorstep
and could also be interfaced with a security camera or lights. The opportunities are unlimited.
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