ECS Overview

The ECS is a mobile monitoring device designed to accurately measure and log the temperature and light levels in any given environment. Through the parallel port a GUI control is able to monitor the current reading from the sensors and display them graphically on a grid. Other functions include a heating and cooling thermostat, light preference control, and loading past environmental data. This gives the user not only the ability to maintain a relatively stable temperature and light levels in a room, but also observe the environmental temperature and light patterns, allowing strategic cooling, warming and lighting to take place.

This system is not only ideal of environmental research, but also useful for maintaining room temperatures and sufficient light levels as it is able to automatically turn on lights, cooling fans and heaters, making closed environments

Limitations:

Thermistor Linearization:

NTC thermistors are simply temperature-dependent resistors. Unfortunately the resistance vs. temperature relationship is not very linear (see figure 1). By itself the thermistor temperature reading are not be very accurate. However there are several techniques that can be applied to improve the accuracy and linear relationship of the thermistor. Cited from http://www.maxim-ic.com/

Thermistor Behaviour (figure 1)

By placing the thermistors in series with a normal resistor we can achieve "Voltage Mode Linearization" (see figure 2 below)

By altering the the resistance value of the resistor in series with the thermistor we are able to alter the symmetric of the linear relation from 25 degrees to 20 degrees so that it is more suited to our temperature range of 0-40 degrees. (see figure 3 below)

Voltage Mode Linearization (figure 2)

Output voltage (figure 3)

Un-calibrated light sensors

We chose not to bother properly calibrating our light sensors as we could not find a suitable light measuring device to calibrate against. Our light sensor section is focused more on indicating the changes in light over a period of time.
Our scale is from 0 to 4050 lux. This was rated against the following table (www.engineeringtoolbox.com). The scale is rate more towards Indoors than out doors.

The table below is guidance for recommended light level in different workspaces:

Activity	Illumination (lux, lumen/m²)
Warehouses, Homes, Theaters, Archives	150
Easy Office Work, Classes	250
Normal Office Work, PC Work, Study Library, Groceries, Show Rooms, Laboratories	500
Supermarkets, Mechanical Workshops, Office Landscapes	750
Normal Drawing Work, Detailed Mechanical Workshops, Operation Theatres	1,000
Detailed Drawing Work, Very Detailed Mechanical Works	1,500 - 2,000

Common light levels outdoor at day and night can be found in the table below:

Condition	Illumination
Condition	(ftcd)	(lux)
Sunlight	10,000	107,527
Full Daylight	1,000	10,752.7
Overcast Day	100	1,075.3
Very Dark Day	10	107.53
Twilight	1	10.75
Deep Twilight	.1	1.08
Full Moon	.01	.108
Quarter Moon	.001	.0108
Starlight	.0001	.0011
Overcast Night	.00001	.0001

Graphing accuracy

The Data from the sensor are accurate to 1/100 of a degree. However on the graph the values are reduced to 1/10 of a degree. We see that 1/100 of a degree to too small to be able to see on the grid.

Simulated Heaters

Our system only simulates the heated with a Red LED. Realistically it would trigger a fan heater of some kind.