Keywords: iButton, iButtons, 1-wire, unique address, 64-bit, serial number, interface, durable, secure, temperature, humidity, applications, blue dot, RFID alternative, life science, medical, supply chain, asset tracking, auto id, SHA2, access control
The Can and Grommet
An iButton device 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 iButton device to just about anything. The two contacts are separated by a polypropylene grommet.
By simply touching the iButton device 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 and overdrive mode. For more information, see Maxim application note 3989, Add Control, Memory, Security, and Mixed-Signal Functions with a Single Contact.
Each iButton device 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 device.
The iButton product line now comprises over 20 different products with different functionality added to the basic button. iButton devices come in the following varieties:
See Maxim tutorial 1796, Overview of 1-Wire Technology and Its Use for more details about the products.
Information is transferred between an iButton device and a PC with a momentary contact. There are many ways to do this. The DS1402-RP8 touch and hold probe shown on the left is one example of an iButton accessory that can be used to communicate with an iButton device.
Another option is the Blue Dot™ receptor. You simply touch your iButton device to a Blue Dot receptor or other iButton probe, which is connected to a PC. The Blue Dot receptor is cabled to a 1-Wire adapter that is attached to a spare PC port. 1-Wire adapters exist for USB, serial, and parallel ports. The Blue Dot receptor and 1-Wire adapter are inexpensive. Order directly from Maxim, or see our distributor websites for pricing and availability.
The iButton device is also the ultimate information carrier for automatic identification, secure authentication, and many portable applications. All of the latest handheld computers can communicate with iButton devices. For a full listing of all portable devices that communicate with iButton devices, see the iButton page on the Maxim website. There are many accessories available from Maxim to help with any possible applications a user may have.
The silicon chip within the iButton device is protected by highly durable stainless steel. You can drop an iButton device, step on it, or scratch it. iButton devices are wear-tested for 10-year durability. The package is not waterproof, though. However, Maxim provides the DS9107, which is a capsule that can be used to achieve IP68-level solvent resistance with an iButton device.
The iButton device is ideal for any application where information needs to travel with a person or an object. The following are some of the application areas where iButton devices are used today and have been used consistently for decades.
Let’s look at a few practical examples of iButton device usage.
The following pictures show a couple of typical shipping flows for a temperature and humidity controlled medical shipment. Once placed in a medical transport container and instructed to start its mission, an iButton device can log the temperature and humidity throughout its journey. The duration and recording intervals can be variable. iButton devices are available as a standalone temperature logger (Thermochron®) or a combination temperature and humidity logger (Hygrochron™). The user can choose either, based on the application needs.
In the following example (Figure 1) the shipment is going a short distance in the same city and the temperature needs to be monitored throughout the trip. This is easily accomplished by using an iButton device that is shipped with the supply.
Figure 1. iButton usage in life science – supply chain management (short haul).
At the manufacturer, the iButton device is instructed to start recording the temperature. Once it has reached its destination, the temperature recorded in the iButton device will be read and evaluated to see if the proper temperature was maintained throughout the journey. If the temperature was maintained, the shipment will be accepted. Otherwise, it will be rejected.
The following example (Figure 2) is very similar to the short-haul example, but it shows that the iButton device has the capability to collect data for a longer period of time, if needed.
Figure 2. iButton usage in life science – supply chain management (long haul).
iButton devices can also be used as electronic asset tags to store information. This may be needed to keep track of valuable capital equipment. Figure 3 shows an example of a simple vehicle tracking system. Each of the vehicle keys has an iButton device affixed to it. Each of the iButton devices has a unique identification number assigned to it.
Figure 3. iButton device usage in asset tracking.
Once the key is checked out by a driver from the hypothetical Key Check Out System, that key gets assigned to that driver. At the same time, various data can be recorded. This may be the time of the day the key was checked out or on what purpose that vehicle was needed and for how long. Once the key is checked back in, the check-in data can be compared to the check-out data and any discrepancy can be addressed. The iButton device’s rugged construction is vital for this kind of application.
Affixed to a key fob, an iButton device can grant its owner access to a cabinet, a piece of equipment, or even a building. The iButton device can also be used as an electronic asset tag to store information. This can be used to keep track of valuable materials such as medical reagents that are used in scientific research. Figure 4 shows such an example.
Figure 4. iButton device usage in access control and usage tracking.
In Figure 4, regulated and tracked medical reagents are stored in a secure cabinet. A researcher first checks out an item and the iButton device logs the ID# of the person checking out the item. Thus, the item can be traced back to that person, if needed. Once the task is completed, the researcher can input the amount that was used in the check-in system and it can be stored in the iButton device. The iButton device thus can be a very useful tool to keep track of and log all activities and resources in a controlled environment.
In addition, some iButton devices can also be used to store electronic cash for small transactions, such as transit systems, parking meters, and vending machines.
There are four components fundamental to any iButton application:
That is all you need to get started. For more details, see the iButton page on the Maxim website.
When developing an iButton solution for an application, you can consider many complementary technologies. Bar codes, RFID tags, magnetic stripe cards, and smart cards are some of the possibilities. Unlike bar codes and magnetic stripe cards, most of the iButton devices can be read AND be written to. In addition, the communication rate and product breadth of iButton devices go 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 device.
There are over 350 million iButton devices currently in circulation, with a very long list of users spanning a wide range of industries. For more information on the various iButton products and applications, see the iButton page on the Maxim website.
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APPLICATION NOTE 3808,AN3808, AN 3808, APP3808, Appnote3808, Appnote 3808