Dr. Ahmed G. Abo-Khalil

Electrical Engineering Department


1-Wire is a device communications bus system designed by Dallas Semiconductor Corp. that provides low-speed data, signaling, and power over a single signal. 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.

One distinctive feature of the bus is the possibility to use only two wires: data and ground. To accomplish this, 1-wire devices include an 800 pF capacitor to store charge, and power the device during periods where the data line is used for data.

Dependent on function, native 1-wire devices are available as single components in integrated circuit and TO92 packaging, and in some cases a portable form called an iButton that resembles a watch battery. Manufacturers also produce products that are more complex than a single component, and use the 1-wire bus to communicate.

A 1-Wire device may be just one of many components on a circuit board within a product, but are also found in isolation within devices such as a temperature sensor probe, or attached to a device being monitored. 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, Parallax Propeller, PICAXE, the Microchip PIC family and RENESAS 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. Alternatively, the connection can be semi-permanent with a different socket type; the iButton clips into it, but is easily removed.

The Java Ring, a ring-mounted iButton with a Java Virtual Machine compatible with the Java Card 2.0 specification within, was given to attendees of the JavaOne 1998 conference.

Each 1-Wire chip has a unique code buried within it. This feature makes the chips, especially in an iButton package, suitable for use as a key to open a lock, arm and deactivate burglar alarms, authenticate computer system users, operate time clock systems, and other similar uses. iButtons are used as Akbil smart tickets for the Public transport in Istanbul.

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