1-Wire

1-Wire is a registered trademark of Dallas Semiconductor Corp. for a device communications bus system designed by Dallas Semiconductor that provides low-speed data, signaling and power over a single signal, albeit using two wires, one for ground, one for power and data. 1-Wire is similar in concept to I²C, but with lower data rates and longer range. It is typically used to communicate with small inexpensive devices such as digital thermometers and weather instruments. A network of 1-Wire devices with an associated master device is called a "MicroLan", that term being trademarked by Dallas.

One of the attractive features of the bus is that a device only needs two wires: data and ground. To accomplish this, the integrated circuit includes an 800 pF capacitor to power it from the data line. Some of the devices are available in tiny cans that look like small capacitors or watch batteries, in which packaging they are called iButtons.

1-Wire devices are also found mounted on printed circuit boards, with or without a 1-Wire controller. Sometimes the PCB is only there to support the 1-wire device, but in many commercial applications, the 1-Wire device is just one of the chips creating the solution to some need. They are sometimes present in laptop and cellphone battery packs, for instance.

Some laboratory systems and other data acquisition and control systems connect to 1-wire devices using cords with modular connectors or with CAT-5 cable, with the devices themselves mounted in a socket, incorporated in a small PCB, or attached to the object being monitored. In such systems, RJ11 (6P2C or 6P4C modular plugs, commonly used for telephones) are popular.

Systems of sensors and actuators can be built by wiring together 1-Wire components, each including all of the logic needed to operate on the 1-Wire bus. Examples include temperature loggers, timers, voltage and current sensors, battery monitors, and memory. These can be connected to a PC using a bus converter. USB, RS-232 Serial, and parallel port interfaces are popular solutions for connecting the MicroLan to the host PC. MicroLans also interface to microcontrollers, such as the Arduino, Parallax BASIC Stamp and the Microchip PIC family.

The iButton (also known as the Dallas Key) is a mechanical packaging standard that places a 1-Wire component inside a small stainless steel "button" similar to a disk-shaped battery. iButtons are connected to 1-Wire bus systems by means of sockets with contacts which touch the "lid" and "base" of the canister. The connection can be fleeting, comparable to a thumb being scanned by a fingerprint reader. iButtons are used as Akbil smart tickets for the Public transport in Istanbul. Alternatively, the connection can be semi-permanent with a different socket type; the iButton clips into it, but is easily removed.

The JavaRing, a ring-mounted iButton with a Java Virtual Machine (compatible with the Java Card 2.0 specification) within was presented to the attendants of the JavaOne 1998 conference.

Each individual 1-Wire chip has a unique code buried within it. Every chip has a different number. This feature makes the chips, especially in an iButton package, ideal as keys, in sense of the device which opens a lock. There are iButton solutions to securing premises, arming and deactivating burglar alarms and other uses. There are also systems for unlocking less obvious secure areas. For example, iButtons can be used to authenticate computer system users, or with time clock systems.

Contents

• 1 Use of the bus
• 2 Example communication with a device
• 3 See also
• 4 References
• 5 External links

Dimensional analysis

n mathematics and science, dimensional analysis is a tool to understand the properties of physical quantities independent of the units used to measure them. Every physical quantity is some combination of mass, length, time, electric charge, and temperature, (denoted M, L, T, Q, and Θ, respectively). For example, velocity, which may be measured in meters per second (m/s), miles per hour (mi/h), or some other units, has dimension L/T.

Dimensional analysis is routinely used to check the plausibility of derived equations and computations. It is also used to form reasonable hypotheses about complex physical situations that can be tested by experiment or by more developed theories of the phenomena, and to categorize types of physical quantities and units based on their relations to or dependence on other units, or their "dimensions", or their lack thereof.

The basic principle of dimensional analysis was known to Isaac Newton (1686) who referred to it as the "Great Principle of Similitude"^[1]. Important contributions were made by the 19th century French mathematician Joseph Fourier,^[2] based on the idea that the physical laws like F = ma should be independent of the units employed to measure the physical variables. This led to the conclusion that meaningful laws must be homogeneous equations in their various units of measurement, a result which was eventually formalized in the Buckingham π theorem. This theorem describes how every physically meaningful equation involving n variables can be equivalently rewritten as an equation of n − m dimensionless parameters, where m is the number of fundamental dimensions used. Furthermore, and most importantly, it provides a method for computing these dimensionless parameters from the given variables.

A dimensional equation can have the dimensions reduced or eliminated through nondimensionalization, which begins with dimensional analysis, and involves scaling quantities by characteristic units of a system or natural units of nature. This gives insight into the fundamental properties of the system, as illustrated in the examples below.

Contents

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• 1 Introduction
  • 1.1 Definition
  • 1.2 Mathematical properties
  • 1.3 Mechanics
  • 1.4 Other fields of physics and chemistry
  • 1.5 Commensurability
  • 1.6 Polynomials and transcendental functions
  • 1.7 Incorporating units
  • 1.8 Position vs displacement
  • 1.9 Orientation/Frame of reference
  • 1.10 Other uses
• 2 Examples
  • 2.1 A simple example: period of a harmonic oscillator
  • 2.2 A more complex example: energy of a vibrating wire
• 3 Extensions
  • 3.1 Huntley's extension: directed dimensions
  • 3.2 Siano's extension: orientational analysis
• 4 Percentages and derivatives
• 5 Dimensionless
  • 5.1 Dimensionless constants
  • 5.2 Dimensionless theories
• 6 Applications
  • 6.1 Mathematics
  • 6.2 Finance, economics, and accounting
• 7 See also
• 8 Notes
• 9 References
• 10 External links