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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. For system 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.
A silicone 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: &# 61623; Powered by vehicle ignition &# 61623; Uses a remote temperature sensor mounted close to the road surface &# 61623; Display is a single tri-color Light Emitting Diode (LED) &# 61623; Mounted on the drivers console &# 61623; Three modes indicating variations of external temperature &# 61623; 0 C = 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, IC 1 a, creates a constant current through the sensor diode, D 1. IC 1 b 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. IC 1 c is a comparator that compares the voltage output of IC 1 b to the desired thresholds of 0 C and 4 C and controls the red / green LED switch over at 4 C.
IC 1 d is a secondary comparator, configured as an oscillator, which controls the red / green LED when the readings fall below 0 C. The simple 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 ensure success.
Several tests should be conducted prior to installation and use. First, using a voltage meter, the resistance across the power leads, and between the + 5 V and 0 V lines on the circuit board should be measured to see if there are any shorts. Then with the meter check that IC 1 a is receiving a 5 V supply across its power pins (11 and 4). If things check O. K. , remove the power and install IC 1 a in its socket.
Once all the components are installed together, its time to calibrate VR 1 and perform an integrated system test. To simulate weather conditions below 0 C, 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. Once 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 VR 1 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 switch location. Once the 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 interesting too. Bibliography: Dell, Steve, "everyday Electronics/ETI, January 2000: "Vehicle Frost Box", Wimborne Publishing Ltd. 1999
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