Keypads Buying AdviceA keypad
is a set of buttons arranged in a plastic or metal block which
usually bear digits and other symbols but not a complete set
of alphabetical letters. If it mostly contains numbers then it
can also be called a numeric keypad. Others like fingerprint
sensor and optical sensors. |
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Most keypads allow users to press keys or enter codes to
control equipment, machinery and for household usages. People can
set one person or multiple people to access to the keypads. Keypads
use several basic switching technologies. Direct membrane keypads
include a membrane painted with conductive ink, a spacer, and a
substrate. Holes punched in the spacer are arranged so that pressing
a key deflects the contacts on the membrane to complete the circuit
on the substrate. Indirect full-travel membrane keypads mount keys
above three layers of punched, flexible polymer sheets that are
sandwiched together. Circuits are silk-screened with a conductive
silver ink on both the top and bottom membrane layers. A middle
spacer separates the two circuits and holes punched in the top
spacer are arranged so that pressing a key deflects the top circuit
to connect with the bottom circuit. Carbon pill keypads contain
protruding, pill-shaped covers that are molded over the top of each
key. When a key is pressed, the conductive pill actuates a pad
trace. The average life for a carbon pill exceeds 5 million
actuations. The contact resistance is usually less than 200 W.
Usually all keypads are programmable, 4-8 digits of codes could be
preset. Each keypad could have over 100 million combinations of
codes to set. Standard keypads mount on the front or rear of panels
and are made from a variety of plastic, thermoplastic, and metallic
materials. There are four standard keypad sizes: 1 x 4, 3 x 4, 4 x 4
and 5 x 4. For each keypad size, the first number indicates the
number of columns and the second indicates the number of buttons.
For example, 1 x 4 keypads have one column and four rows of buttons.
3 x 4 keypads are telephone-style devices with three columns and
four rows of buttons. 4 x 4 keypads have four columns and four by
rows of buttons. 5 x 4 keypads have five columns and four rows of
buttons. Electrical switch specifications for standard keypads
include maximum current rating, maximum alternating current (AC)
voltage rating, and maximum direct current (DC) current rating.
Standard keypads with X-Y outputs are matrix-style devices. Devices
with a single pole or common bus outputs require the same number of
pins as buttons. Standard keypads are often backlit and include
light emitting diodes (LED) to indicate process status, system
functions, machine interlocks, and alarm conditions. Embossed
switches have graphics or alphanumerical characters that are raised
from switch surface. Switches, panels and keypads that are designed
for outdoor use are water resistant or waterproof and can withstand
both ultraviolet (UV) light and variations in temperature. Standard
keypads that are used in medical and electronics applications
provide protection from electromagnetic interference (EMI), radio
frequency interference (RFI), and electrostatic discharge (ESD). ESD
protection may be accomplished with static-dissipative or conductive
elements in the switch material, or through special electronics
grounding.
Buying suggestions
Pay attention to
the material used for the keypad you selected. Some of the touch
screen keypads make sure there is not defection on the LCD screen.
Keep the receipt well and leave your exact address and phone number
for convenience of free installation. Also, test for the code setup
process and check how it works and make sure it can be easily
operated.
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