The system I
choose to research is a simple ?open-looped system? called the
?Vehicle Frost Box?. This system is used to informing motor vehicle
operators that likely conditions for icy roads are developing. Black
ice cannot be seen and is a prime contributor to vehicle accidents
during the winter months. If used, this simple system could actually
save precious time, money and physical injury.
development, the ?Problem Statement? is; ?Black ice cannot be seen on
roads, causing safety hazards for drivers.? Next, the ?Need
Statement? is; ?We need a way to determine when favorable weather
conditions exist to form black ice on roads?. Last, the ?Requirement
Statement? consists of the following: the system must be cheep,
reliable, and linear, with a low thermal mass allowing a quick
response to variation in air temperature.
There is a
system already in use that is cheep. This system uses a liquid
crystal strip attached to the drivers wing mirror. However, this
attachment location is too high from the ground to properly determine
road conditions. Additionally, some cars have heated mirrors, which
would render this system useless.
semiconductor junction, in the shape of a diode was chosen to build
the design around. This option filled all the requirements listed in
the ?Requirement Statement?. Optional sensor devices were
thermistors, thermometers, and thermocouples. These options were
discarded because of high cost.
The basic design
of the frost box follows:
remote temperature sensor mounted close to the road surface
Display is a
single tri-color Light Emitting Diode (LED)
the drivers console
indicating variations of external temperature
* 4C =
steady green light
* 4C =
steady red light
* 0C =
alternating green & red light
The design is
based around a type 324 integrated circuit that contains four op.amp
blocks. Each op.amp block is used in a different way to process the
sensor signal. The first, IC1a, creates a constant current through
the sensor diode, D1. IC1b amplifies the diode voltage variations,
applies voltage of a sensible magnitude and moves the voltage in the
right direction. The voltage output is directly proportional to the
temperature readings from the sensor. IC1c is a comparator that
compares the voltage output of IC1b to the desired thresholds of 0C
and 4C and controls the red/green LED switch over at 4C. IC1d is a
secondary comparator, configured as an oscillator, which controls the
red/green LED when the readings fall below 0C.
design of the frost box lends itself to construction by a ?do it
yourself? person. A materials list is available along with
instructions and the recommended layout for component installation.
Additional advice on technique is provided in the instructions to
should be conducted prior to installation and use. First, using a
voltage meter, the resistance across the power leads, and between the
+5V and 0V lines on the circuit board should be measured to see if
there are any shorts. Then with the meter check that IC1a is
receiving a 5V supply across its power pins (11 and 4). If things
check O.K., remove the power and install IC1a in its socket.
Once all the
components are installed together, it?s time to calibrate VR1 and
perform an integrated system test. To simulate weather conditions
below 0C, place some ice from the freezer with some water in a
pitcher. A thermometer is used to validate the temperature of the
chilled water used in testing.
conditions are set up, apply power to the circuit. Then dip the diode
in the water, being careful to keep the sensor away from the ice.
Calibrate VR1 by adjusting the preset pot until the LED is flashing
red/green. After calibration is complete, remove the diode from the
chilled water. The LED should stop flashing and turn steady red, and
then to green. Repeat this process to validate the system is
operational. The system is now ready for installation.
The first thing
to decide, in the installation process, is where to place the three
main components of the system. The sensor diode should be placed as
low to the ground as possible. Two areas are recommended. Behind the
front license plate or in a protected area within a forward wheel
well. Next are the LED and the Box. If both are going on the
dashboard the LED may be mounted on the Box itself. If a separate
mounting is preferred, then the Box can be mounted under the dash and
the LED can be mounted in another small box, or in an unused vehicle
location is determined for all the components. Measurements are taken
to determine length for the wires that connect the system. Care must
be taken to insure the wire path is protected from fraying, corrosive
conditions and moving vehicle parts.
Now that the
Frost Box is installed and operational, the operator will be able to
determine black ice conditions. The primary application for the Frost
Box is installation on motor vehicles. Another application for the
Frost Box is installation in green houses, to determine when heating
should be turned on.
I found this
system interesting to report on. Not only because of its simple
design, but because my husband constantly warns me to be careful
during the inclement winter weather here in Ohio. I hope you found it
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