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Keywords: USB on-the-go (OTG), Android, 1-Wire
APPLICATION NOTE 5705
INTERFACE 1-WIRE USB ADAPTER WITH
ANDROID
By: Wilson Tang, Member of Technical Staff
Abstract: This application note details how to interface the DS9490R, temperature logger iButton devices,
and Android over USB On-the-Go (OTG). The communication protocol between each section is reviewed.
We review the data sheet information and how to apply it in the end system. A sample Android application
illustrating the example code is also available for download.
A similar version of this article appeared December 1, 2013 on Electronic Products.
Associated software is available for download.
Introduction
Look around. Smartphones are ubiquitous. Far more than a mere telephone, a smartphone is a powerful
computer that fits in your pocket. Since the computing power and sensors available in a smartphone
continue to increase, it is now practical to use that phone as the interface to other devices. This article
shows how to use the USB port on an Android smartphone to communicate with slave devices without a
computer system. This example here uses the 1-Wire bus for communication by USB from the Android
to a Thermochrom iButton temperature logger.
System Layout
Crucial to this application is the USB port on the smartphone. When the smartphone uses a USB on-the-go
(OTG) transceiver, then USB host functionality is possible with other slave devices, such as mice, flash
drives, keyboards, or the Thermochron here. Recent versions of the Android application programming
interface (API) support USB host mode at the application level. This functionality lets end users install
applications that "talk" with USB peripherals without rooting or installing special drivers on the user's
smartphone.
The system block diagram is in Figure 1. The Android smartphone must use a USB OTG transceiver.
Normally, the phone is connected to a computer and acts as a USB slave, but the USB OTG transceiver
allows the phone to be transformed into a USB master. This role reversal requires a special OTG cable to
provide the USB type A port and to signal that a USB slave is connected to the smartphone.
This application is a master–slave system with the Android smartphone as the master and the
Thermochron data logger as the slave. The system uses a USB to 1-Wire/iButton (DS9490R) adapter to
bridge the smartphone with the data logger. A network cable/socket, the DS1402D-DR8, is used as the 1-
Wire bus, which only requires one data line. The data logger is the iButton Thermochron (DS1921G).
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