Specifications

35
the relay receives the correct current and voltage. Another option for this step is
to use a relay driver which is a surface mount chip with several transistor circuits
inside. The advantage of this type of device is that the design is simplified
because the designer does not have to implement multiple complex circuits into
the design of the printed circuit board. This will be discussed further in the Relay
subsection of the Design portion of this paper.
2.5 LCD Touch Screen
For the Efficient HVAC Control and Feedback System, system navigation and the
user inputted settings can be achieved via the touch display or touch screen
feature. Many electronic appliances now use touch screen displays such as
laptops, palm pilots, blackberries, and music players. These devices all utilize a
touch screen sensor, a controller, and software driver. The various touch display
technologies that are available today are resistive touch screen, surface acoustic
wave technology, and the capacitance touch display panel. All of these touch
display technologies are touch sensors which normally have an electric signal go
through the layers of the screen causing the a voltage to change. The voltage
change will directly link to help telling it the location of the finger touching the
screen.
In the resistive touch screen system, it primarily contains two electrically
conductive layers separated by a narrow gap called a spacer. A current flows
through the two layers of the touch display screen while the monitor is still
running. This system is composed of a glass panel and when the finger is
pressed down on it, it will lock on that exact point in the x-y coordinate plane.
The concept of the voltage divider is used to calculate the x-y coordinate that has
been touched. When the electric field in the touch screen system is changed, the
software driver translates the touch information to the operating system so the
location of the touch can be identified. Figure 11 below includes a step by step
process as to what occurs in a resistive touch screen system.
Figure 11 Resistive touch screen (Reprinting Permission Requested from
3M Touch)