DATEL, Inc., Mansfield, MA 02048 (USA)
Tel: (508)339-3000, (800)233-2765 Fax: (508)339-6356
Email: sales@datel.com
Internet: www.datel.com
DATEL makes no representation that the use of its products in the circuits described herein, or the use of other technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained
herein do not imply the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifications are subject to change without notice. The DATEL logo is a registered DATEL, Inc. trademark.
The LED versus LCD Decision
Introduction
Users of contemporary digital panel
meters (DPM's) have a variety of options
available to them. While options are nice,
they invariably mean more choices have
to be made. After determining what meter
resolution one requires, the next most
basic decision is usually which type of
display to use -- liquid crystal or light
emitting diode?
Traditionally, liquid crystal displays (LCD's) have been the
obvious choice for outdoor/daylight applications and/or for
applications requiring extremely low power consumption (current
drains less than 15mA). Light emitting diode (LED) displays, with
their comparatively low light intensities and relatively high current
drains, have been excluded from these more demanding
applications.
Recent DATEL innovations, most notably the introduction of
extremely low-power LED displays, have complicated the once
straightforward, LED/LCD decision.
LED Displays
The majority of panel-meter applications can, and should, use
LED displays for two reasons: LED's can be read from virtually any
angle (LCD's have much more restricted viewing angles), and LED
displays can be easily read from greater distances (assuming
comparable digit sizes). Additionally, LED's are typically more
durable than LCD's and can be used under more harsh environmen-
tal conditions. The response time of LCD's slows down noticeably
as temperatures drop below 0C (32F). This effect is seen as a
"ghosting" of segments (old data remains partially visible) after the
display has been updated with new data. The response time of
LED's is not visibly affected even at temperatures below 20C.
LCD Displays
LCD digital panel meters should always be used when the meter
has to be read in direct sunlight, i.e., when no shading of the display
is possible. Even the newest, super bright, high-intensity, red LED's
(similar to those used in DATEL LED meters with "RH" suffixes) get
"washed out" when viewed in direct sunlight. These bright LED's
become easily visible, however, when hoods or other shading
devices are used.
Backlit LCD displays should be
used if the meter is to be operated in
both high and low-light conditions.
DATEL uses reliable, long-life LED's as
the light source in all of our backlit LCD
meters. A "B" suffix added to the end of
the DATEL model number specifies a
backlit model.
Transflective displays (black
segments on a light-green background) are featured on all backlit
LCD meters. Reflective displays (black segments on a silver
background) are used on non-backlit devices.
Backlighting detracts from the low-power appeal of LCD meters.
Backlit models of DATEL's LCD meters typically draw 35mA from
their +5/9V supply. Non-backlit LCD models typically draw 100's of
microamps. Current drains for backlit models can be reduced with
the installation of current-limiting series resistors between the supply
and the backlighting pin. This results in a proportionately dimmer
backlighting effect, however, effective compromises can usually be
found. Refer to the individual product data sheets for more
information on backlight dimming.
Portable Applications
Portable instruments, specifically battery-powered designs
requiring continuous operation, should use LCD meters. This is
particularly true if the current drain on the battery must be
maintained below 1mA. As mentioned above, DATEL now offers
low-power LED panel meters with current drains less than 10mA
from a single +5V power supply. These low-power LED models
usually have red displays and are designated with an "RL" suffix
added to the end of the part number.
If continuous display operation is not required, the DMS-20PC-
RL (3 digits, subminiature package, low-power red LED display)
has a DISPLAY ENABLE feature allowing users to dim or totally
darken the LED's. In the dark mode, current drain of this meter is
reduced to less than 0.5mA (500A). Even at full brightness, the
DMS-20PC-RL draws a mere 7mA. Low-power LED meters are
available in both 3 and 4 digit resolutions and only from DATEL!
DMS APPLICATION NOTE
PDF 
ZIP