Featured Medical Application - Personal Activity Monitor

Accelerometers are electromechanical devices used to measure acceleration, or rate of change in velocity over time, and are used to sense vibration, shock, and orientation. Accelerometer types and technologies can vary depending on product size and application. Pedometers and activity monitors that make use of accelerometers can achieve high accuracy and reliability.

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A temperature sensor is a device that measures cold or heat as a temperature or temperature gradient. Many applications require some implementation of temperature sensing and measurement. For medical applications a sensor with high resolution can be desirable, because the range of human body temperatures may span only a very small part of the sensor's dynamic range.

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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.

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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.

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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.)

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Battery protection circuits are an electronic safeguard to prevent damage to internal electronics in the event of reverse battery installation, accidental short circuiting, or other inappropriate operation. The simplest protection for reverse battery protection is a diode in series with the battery, however protection circuit ICs offer more than just battery protection and can increase the useful operating life of a rechargeable battery pack.

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Real Time Clocks (RTCs) are IC devices that keep track of time. A typical RTC can provide the time of day as well as the date via a serial bus such as I ² C or SPI. Although similar in many ways, RTCs should not be confused with clock generators, which are used to synchronize various parts of a circuit.

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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.

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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.

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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."

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Battery charging circuits are used to recharge batteries and are available in linear or switching topologies. They can be completely autonomous in operation or used with a microcontroller. Generally speaking, integrated chip charging technology can produce charge currents in a range from around 625 nA, to more than 4.5A. Battery charger IC s often do more than just charge; they can protect from overcharging, regulate voltage, and manage charging from irregular sources such as energy harvesters or very low voltage sources. In portable technology, battery chargers are indispensable.

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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."

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Bluetooth is the most widely supported technology standard for short-range wireless communication between multiple devices. Bluetooth allows for simple, versatile wireless communication, and using a method of FHSS (Frequency Hopping Spread Spectrum), is highly resistant to interference and inherently secure. With nominal data rates of 3 Mb/s (Bluetooth 2.0) and 24 Mb/s (3.0+HS, 4.0), Bluetooth is suitable for exchanging small files and streaming audio.

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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.

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Electrostatic Discharge ( ESD ) is an instantaneous electric current that flows from a higher to a lower voltage potential without warning. One of the more well-known causes of ESD is static electricity, which is created when insulator surfaces rub together. Permanent damage can occur to semiconductor devices that are exposed to ESD . An ESD current waveform has an extremely fast rise time. ESD protection chips can be very effective but consume board space and add capacitance to an I/O line.

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A Power Management Integrated Circuit ( PMIC ) is a special-purpose IC that provides one or more power management related functions. These can include voltage regulation, DC/DC conversion, battery management capability and more. Many PMICs offer an I ² C and/or SPI bus interface, and some might provide additional features such as an integrated touch screen interface.

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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. LCD s 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.

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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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An AC/DC adapter is a type of external power supply, often enclosed in what looks like an over-sized AC wall-plug . Other names include power adapter, power converter, plug-in adapter, adapter block, domestic mains adapter, line power adapter, or simply AC adapter. AC adapters are used with electrical devices that require DC power but do not have the internal circuitry to accomplish the conversion of AC to DC. Medical-grade power supplies are designed to meet the IEC60601-1 medical equipment safety standard and may include typical output voltages of 3.3 to 48 Vdc, a variety of package style (open-frame, enclosed, encapsulated, etc.), mounting options, thermal management, and environmental features, among others.

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