This article will give basic overview of iButton functionality and usage. Example of iButton usage with complete source code can be read in article iButton AVR readout example project used with DS1990R-F5. The iButton is a computer chip enclosed in a 16mm thick stainless steel can. Because of this unique and durable container, up-to-date information can travel with a person or object anywhere they go. The steel iButton can be mounted virtually anywhere because it is rugged enough to withstand harsh environments, indoors or outdoors. It is small and portable enough to attach to a key fob, ring, watch, or other personal items, and be used daily for applications such as access control to buildings and computers, asset management, and various data logging tasks.
iButton Components: The Can and Grommet
iButton Can An iButton uses its stainless steel 'can' as an electronic communications interface. Each can has a data contact, called the 'lid', and a ground contact, called the 'base'. Each of these contacts is connected to the silicon chip inside. The lid is the top of the can; the base forms the sides and the bottom of the can and includes a flange to simplify attaching the button to just about anything. The two contacts are separated by a polypropylene grommet.
The 1-Wire Interface
1-Wire Interface By simply touching the iButton to the two contacts described above, you can communicate with it through our 1-Wire protocol. The 1-Wire interface has two communication speeds: standard mode at 16kbps, and overdrive mode at 142kbps.
What Is 1-Wire Technology?
The basis of 1-Wire technology is a serial protocol using a single data line plus ground reference for communication. A 1-Wire master initiates and controls the communication with one or more 1-Wire slave devices on the 1-Wire bus (Figure 1). Each 1-Wire slave device has a unique, unalterable, factory-programmed, 64-bit ID (identification number), which serves as device address on the 1-Wire bus. The 8-bit family code, a subset of the 64-bit ID, identifies the device type and functionality. Typically, 1-Wire slave devices operate over the voltage range of 2.8V (min) to 5.25V (max). Most 1-Wire devices have no pin for power supply; they take their energy from the 1-Wire bus (parasitic supply).
What Is Special About 1-Wire?
1-Wire is the only voltage-based digital system that works with two contacts, data and ground, for half-duplex bidirectional communication. In contrast to other serial communication systems such as I²C or SPI™, 1-Wire devices are designed for use in a contact environment. Either disconnecting from the 1-Wire bus or a loss of contact puts the 1-Wire slaves into a defined reset state. When the voltage returns, the slaves wake up and signal their presence. With only one contact to protect, the built-in ESD protection of 1-Wire devices is extremely high. With two contacts, 1-Wire devices are the most economical way to add electronic functionality to nonelectronic objects for identification, authentication, and delivery of calibration data or manufacturing information.
Each iButton has a unique and unalterable address laser etched onto its chip inside the can. The address (e.g. 2700000095C33108) can be used as a key or identifier for each iButton.
The iButton product line now comprises over 20 different products with different functionality added to the basic button. iButtons come in the following varieties:
* Address Only
* Real-Time Clock
* Data Loggers
How Durable Is the iButton?
Mud Photo The silicon chip within the iButton is protected by the ultimate durable material: stainless steel. You can drop an iButton, step on it, or scratch it. The iButton is wear-tested for 10-year durability.
What Can I Do with the iButton?
Door Lock The iButton is ideal for any application where information needs to travel with a person or object. Affixed to a key fob, watch, or ring, an iButton can grant its owner access to a building, a PC, a piece of equipment, or a vehicle. Attached to a work tote, it can measure processes to improve efficiency, such as manufacturing, delivery, and maintenance. Some iButton versions can be used to store electronic cash for small transactions, such as transit systems, parking meters, and vending machines. The iButton can also be used as an electronic asset tag to store information needed to keep track of valuable capital equipment.
What Do I Need to Put Together an iButton Application?
There are four components fundamental to any iButton application:
* A host system: this can be a PC, a laptop, a handheld computer, or an embedded system.
What Are the Advantages of iButtons Over Other Technologies?
When developing an iButton solution for an application, you can consider many complementary technologies. Bar codes, RFID tags, magnetic stripe, prox, and smart cards are some of the possibilities. Unlike bar codes and magnetic stripe cards, most of the iButtons can be read AND be written to. In addition, the communication rate and product breadth of iButtons goes well beyond the simple memory products typically available with RFID. As for durability, the thin plastic of smart cards is no match for the strength of the stainless-steel-clad iButton.
Who Is Using the iButton?
With over 175 million iButtons currently in circulation, the list of users is very long.