November 2015
23
I
ndustrial
C
ontrol
& C
ommunications
Future-proof your display in embedded
industrial applications
By David Parsons,
Consultant to Renesas Electronics
This paper examines the key factors
affecting the lifetime of graphic
LCD displays, to help designers reach
the right conclusion and make
decisions suited to particular
circumstances and needs.
The question is: can an LCD panel last
the lifetime of the equipment?
If you select carefully the answer
can certainly be yes!
Choosing a display for a consumer applica-
tion such as a smart phone carries little risk
for the designer from a lifetime perspective,
as the phone often drives sufficient volume to
justify dedicated production or even a custom
display. A new year heralds a new model with
a new display and last year’s model is quickly
discontinued, leaving the unlucky indus-
trial designer with the challenge of finding
a replacement and updating their design in
weeks... rather than investing their resources
in creating new value. Many industrial appli-
cations need to last for many years in produc-
tion, but can an industrial display last for the
production life of the equipment? In many
cases this can be 10 or even 20 years! Is it pos-
sible for a display to be available for such a
long period?
Some areas require careful design consider-
ation and should allow for a degree of main-
tenance or rework without major redesign of
the equipment or front panel. These include
the degradation of the backlight, touchscreen
or simply the phase-out of the panel itself, so
the designer needs to consider the following:
mitigation against the risk of panel obsoles-
cence, mechanical mounting of the display,
backlight technology and its inherent life-
time, touchscreen lifetime (if used), oper-
ating temperature range, and methods of
driving the display.
Industrial graphic displays can easily oper-
ate for more than 10 years. However typical
manufacturing lifetimes for the display can
be as little as a few years, depending on the
manufacturer and intended end use. It should
also be remembered that the rules of supply
and demand apply not only to the LCD man-
ufacturer, but also the suppliers of all the com-
ponents that make a display panel. Careful
selection is needed.
Monochrome STN displays are still used in
many industrial applications and offer low
cost, small panel sizes ranging from 1” to
around 10”, with resolutions up to VGA (640
x 480 pixels). They are available in reflective,
transmissive and transflective formats and
a wide range of screen shapes. Colour TFT
panels tend to be used in consumer applica-
tions and are exposed much more to risk of
discontinuation. Sizes range from typically
3.5” to 19” with resolutions up to full HD
(1920 x 1080) with standard and wide for-
mat options. Popular sizes are the smaller 5”
or 6.5” displays which offer a good combina-
tion of graphics, brightness and cost, whilst
industries such as factory automation favour
larger 10.4” to 15.6” TFT displays that can
provide higher levels of information and ani-
mation. The useful operating life of an LCD
panel is usually determined by the backlight.
Most manufacturers nowadays employ long
lasting, low power LED backlight technology
to give better brightness, readability and lon-
ger life. These backlights have operating lives
typically around 100,000 hours (backlight
operating life is usually characterized to 50%
maximum brightness). The backlight is also
often replaceable, thus increasing the life of
the panel.
Every panel has to be driven and there are a
number of different possibilities depending
on the resolution. Lower resolution panels
up to around WQVGA (480 x 272 pixels) can
be driven directly from some MCUs without
the need for an external controller. Panels that
have CMOS or TTL interfaces generally do
not require any additional signal drivers, how-
ever low voltage interfaces such as LVDS (Low
Voltage Differential Signalling) will require
specific interface drivers between the MCU
and the panel. Figure 1 shows a typical direct
RGB panel interface with interfaces to the
LCD panel and frame buffer memory. Exam-
ples of direct MCU to LCD interface and a
LVDS equivalent are shown in figures 2 and 3.
Larger resolution panels will require either a
dedicated graphics controller IC or a graphics
control board as the MCU alone cannot pro-
vide the high speed signals required. Inter-
faces to graphics controller ICs typically use
the MCU external peripheral bus dedicated
Figure 1. LCD direct
drive block diagram
