DS1990A iButton : Pin Configuration & Its Applications

An iButton is one kind of small device including a microchip that is covered within strong stainless steel with 16 mm thickness and a button. This device is used to hold the data up to date so that it is durable as well as mountable anyplace even in insensitive outside environments. It is extremely small and moveable so that it can be easily connected to a watch, ring, key fob for access control of computers, devices, etc. This article discusses an overview of the DS1990A iButton and its working with applications.

What is DS1990A iButton?

DS1990A iButton is a marvelous and solid device, launched by Maxim integrated. It has a 64-bit identification number on it for tracing and this number is not changeable. This device looks like a coin and it is a rugged device so that it can resist harsh environments.

This coin-sized device includes a single wire communication circuit, so that transmission of the signal can be done throughout the single wire wireless communication protocol. This protocol includes a data line & a ground line. These iButtons are data carriers, so used in temperature logging, automatic authentication, etc.

In iButton, the higher face of the device is accountable for the transmission of signal whereas the lower face is connected to the GND terminal with a single wire protocol.

Pin Configuration

The pin configuration of a DS1990A iButton is shown below. This button includes two pins where each pin & its functionality is discussed below.

• Pin1 (1-wire Signal): This is a serial I/O pin that is used to transmit & receive the data using this pin.
• Pin2 (GND): This is a reference potential pin

Features & Specifications

The features & specifications of the DS1990A iButton include the following.

• Operating voltage ranges from 2.8 V to 6 V
• Max i/p low voltage is 0.3 V
• Min i/p high voltage is 2.2 V
• I/O sink current is 20 mA
• Input load current normally is 0.25 uA
• The least recovery time is 1 us
• Read time of data max is 15 us
• Operating temperature ranges from -40°C to 85°C
• The serial communication data rate is 16.3 kbps
• It is used through a 64-bit authentication number for proper traceability & uniqueness of a specific peripheral.
• It gives support to a multi-drop bus while connecting several 1-wire devices.
• It includes two variants like F3 & F5
• It is available with a flange/ adhesive backing to attach it to objects.

The block diagram of DS1990A iButton includes an internal circuit that includes ROM, functional control & a parasitic power circuit that includes a parasitic capacitor & a rectifier. An alternate DS1990A iButton device is DS1920, 1972, 1982 & 1991.

• This DS1990A iButton device individually cannot work so it needs particular accessories to use in various projects which include the following.
• For DS9490R or DS9490B adapter is used to connect iButton with a USB port
• DS9101 clip is used to hold iButton
• DS9092 probe is used for the connection of microcontroller or circuit

Components of DS1990A iButton

iButton device includes three components mainly like Can, 1-Wire Interface & the Address.

An iButton device includes a stainless steel ‘can’ that works like an interface for communication. Every ‘can’ includes a data contact namely ‘lid’ & a GND contact namely the ‘base’. Inside of this device, there are two contacts where each contact is connected to the silicon chip

The data contact-like ‘lid’ is arranged at the top of the can and the base structures the sides & the bottom. These two contacts are divided through a polypropylene grommet. By simply touching on the two contacts of this device, the communication can be done throughout the one-wire protocol.

This one-wire protocol has two communication speed modes like standard & overdrive. Every iButton device includes an exclusive & not changeable address laser which is etched onto the can of the chip. The address can be utilized as an identifier or key for every iButton device.

Types of iButton

There are various types of iButtons available in the markets which are categorized based on their functionality. Some of them are Memory, Address only, Real-Time clock, Secure & Data Loggers.

• Memory iButton is used to read or write data that is stored within memory
• Address only is used to read the exclusive identifier
• The real-Time clock includes an integral RTC
• Secure type cannot be hacked and used wherever digital currency is concerned
• Data Loggers are used for humidity or temperature based applications

How to use DS1990A iButton/Circuit Diagram

The iButton interfacing with a microcontroller is shown below. Here any type of microcontroller board can be used like Arduino Uno, Raspberry Pi, PIC, Beaglebone with the connector like DS9092L.

These iButtons are utilized in different electronics mini-projects. Here, a DS9092L probe is used to interface with the microcontroller board. This probe’s ground terminal can be connected toward the microcontroller’s GND pin whereas the Signal pin is connected to the microcontroller’s GPIO pin.

When this device is address-only, then the GPIO pins states will decide the demand for data reading through a 1-wire interface. It needs very little power thus it is appropriate for 3.3V to 5V operating controller units. Here for a 1-wire data line, floating states can be avoided by using a 1k pull-up resistor.

Where to use/Applications

The applications of DS1990A iButton include the following.

The DS1990A iButton is an Address only type so one can simply read the 64-bit unique identifier but cannot write anything in it. For this device, the read time is simply 5ms & it follows 1 wire communication protocol only. So the operator has to touch this device to make it supreme for entry restriction-based projects.

• Security systems
• Identification of product otherwise resource
• Controlling of Inventory
• Serial Data Communication
• Acquisition of data
• For Security
• Access Control
• These are used as information carrier devices for automatic recognition, safe verification & several handy applications.
• Most recent computers can converse with these devices. So, for a complete listing of all moveable devices commune through iButton devices.

Thus, this is all about an overview of the DS1990A iButton data sheet which includes its pinout, features, specifications, and its applications. An iButton device is durable & mountable at any place thus this device can be used to hold the information up-to-date. These devices are small in size and portable. Here is a question for you, what are the drawbacks of iButtons?