1-Wire

1-Wire is a wired half-duplex serial bus designed by Dallas Semiconductor that provides low-speed (standard 16.3 kbit/s; "overdrive" at 10×) data communication and supply voltage over a single conductor.

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. The protocol is also used in small, 16 mm electronic keys known as a Dallas key or iButton.

One distinctive feature of the bus is the possibility of using only two conductors — data and ground. To accomplish this, 1-Wire devices integrate a small capacitor (~800 pF) to store charge, which powers the device during periods when the data line is active.

1-Wire devices are available in different packages: integrated circuits, a TO-92-style package (as typically used for transistors), and a portable form called an iButton or Dallas key which is a small stainless-steel package that resembles a watch battery. Manufacturers also produce devices more complex than a single component that use the 1-Wire bus to communicate.

1-Wire devices can fit in different places in a system. It might be one of many components on a circuit board within a product. It also might be a single component within a device such as a temperature probe. It could be attached to a device being monitored. Some laboratory systems connect to 1-Wire devices using cables with modular connectors or CAT-5 cable. 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 many 1-Wire components. Each 1-Wire component contains 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 a MicroLan to the host PC. 1-Wire devices can also be interfaced directly to microcontrollers from various vendors.

iButtons are connected to 1-Wire bus systems by means of sockets with contacts that touch the "lid" and "base" of the canister. Alternatively, the connection can be semi-permanent with a socket into which the iButton clips, but from which it is easily removed.

Each 1-Wire chip has a unique identifier code. This feature makes the chips, especially iButtons, suitable electronic keys. Some uses include locks, burglar alarms, computer systems, manufacturer-approved accessories, time clocks and courier and maintenance keys for smart safes.