Voltage References for Electronic Weight Scales
A
voltage reference
produces a constant level of voltage over time regardless of load, changes in power supply, or
temperature. Voltage references are used in power supplies, analog-to-digital converters,
digital-to-analog converters, and many other applications where voltage levels must be
maintained at a steady level. Without a voltage reference, precision is greatly affected and may
render the device inoperable.
Voltage references
can vary greatly in performance. A voltage reference for a power supply might hold its output to
within only a few percentage points off of its nominal or stated value; however, a voltage
reference to instrumentation-level standards are measured in parts per million regarding
stability and precision to the nominal or specified value.
Load Cells for Electronic Weight Scales
A
load cell
converts force into an electrical signal. The resistance of the device changes as the force
deforms it, and the change is then measured with a bridge circuit. The resulting differential
signal is generally very small relative to the common-mode voltage, requiring an amplifier with
a sufficiently high common mode rejection ratio (CMRR).
Batteries for Electronic Weight Scales
Batteries
are a portable, wireless means of storing energy via the use of self-contained chemical cells.
They can be for one-time use and discarded, or recharged and reused. In essence, a battery is an
energy storage device, but can only store and release electricity as direct current. Direct
current is a flat line at a given amplitude (until it declines as it is exhausted), versus
alternating current, which is a sinusoidal wave.
Amplifiers for Electronic Weight Scales
Amplifiers
have enormous voltage gain, use feedback to operate, and can be classified in different ways.
They can be identified by the device they are intended to drive (e.g., headphone amplifier,
speaker amplifier), the frequency range of the signal (e.g., RF, Audio), and by the function
that they perform (e.g., low noise amplifier, inverting amplifier, power amplifier.)
Voltage Regulators for Electronic Weight Scales
DC/DC regulators
are circuits that convert DC voltage from one level to another and maintain that voltage to a
constant level.
Electronic systems often have several sub-circuits, each with its own voltage level requirement
that may be higher or lower than the main power supply. Step-up converters or regulators boost a
voltage to a higher level.
Step-down converters
or
regulators
lower (or "
buck
") a voltage to a lower level. DC/DC converters and controllers can also be used for the same
purpose, but may offer options such as multiple softstart levels, undervoltage lockout,
protection against overvoltage and undervoltage, and programmable short-circuit protection. All
of these devices are considered to be in the same category of integrated chips, typically
categorized as power management devices.
ADCs for Electronic Weight Scales
An
Analog-to-Digital Converter
(ADC or A/D converter) measures the magnitude of an input analog signal and converts it to a
digital number that is proportional to the magnitude of the voltage or current. An ADC often
converts signals collected from the real-world to digital signals for processing. One of the
more important specifications of an ADC is the resolution that it offers, which is the number of
discrete values (represented in bits) that the
ADC
produces in relation to the analog signal it is converting. The more bits, the higher the
resolution. A higher resolution yields a more accurate approximation of the analog input.
Fuel Gauges for Electronic Weight Scales
A
battery fuel gauge
, or
state-of-charge
(
SOC
) indication, has evolved from a simple warning to a complex system level use of information,
such as soft shutdown to prevent data loss. Considerations that affect accurate accounting for
remaining battery charge include the effects of aging, self-discharge, and temperature
variations. The value for full capacity is obtained and algorithms are used to calculate the
remaining capacity. The drawback of this approach is that self-discharge is difficult to model
since it is a function of aging and temperature.
MCUs for Electronic Weight Scales
The term "
MCU
" or "
processor
" refers to an electronic device that performs computational functions and carries out the
instructions of a stored program. Other terms for processor are microprocessor, central
processing unit, and digital signal processor. Essentially, the processor refers to "the brains
of a computer."
LED Drivers for Electronic Weight Scales
LED drivers
are used in many applications, but in displays they are a constant-current source commonly used
to power LEDs for screen backlighting. LEDs are current-driven devices whose brightness is
proportional to the magnitude of forward current flow. Desirable features for an LED driver are
tight regulation of current, high efficiency, PWM dimming, overvoltage protection, load
disconnect, small size, and ease of use.
Displays for Electronic Weight Scales
LCD
means "
liquid crystal display
." It is an electronically driven flat panel screen that orients liquid crystals within the
panel in a direction that blocks or transmits light coming from behind the panel. LCDs are a low
cost, energy efficient visual display that can be controlled in segments or as individual
pixels, in shades of black and gray, or in full color. LCDs have most commonly replaced bulky
cathode ray tubes in televisions and computers and are available in all sizes. Liquid crystals
were first discovered in 1888, but were first put into common use in the early 1970s as
electronic digital-display watches.
USB Transcievers for Electronic Weight Scales
USB
is a standard connection interface between computers and digital devices. A
USB transceiver
is a physical layer device that prepares data for transmission and then sends to, and receives
data from, another transceiver. The transceiver detects connection and provides the low level
USB protocol and signaling. The term "transceiver" indicates an implementation of both transmit
and receive functions. It transmits and receives, encodes and decodes data, provides error
indication, implements buffers to stage data until it can be managed, and adjusts for the clock
rate from the serial stream on the USB SuperSpeed bus to match that of the "link layer" higher
up on the communication stack.
Wireless for Electronic Weight Scales
Wireless
technology enables the transfer of information over short or very long distances without cables.
The term "wireless" most often refers to telecommunications. Wireless communication is possible
using a wireless transmitter and corresponding receiver. A wireless receiver refers to the
receiving end of the information transfer and requires less energy to operate than the active
transmitting portion where the transfer originates.
USB Receptacles for Electronic Weight Scales
USB plugs and receptacles
are meant to reduce human error by their unique shape; they fit together in only one way. USB
plugs and receptacles come in Type A (typically connecting to hosts or hubs) or Type B
(typically connecting to devices) and 3 sizes: standard, mini, and micro. Type A plugs always
face upstream, Type B faces downstream.
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