Dan Tudor Vuza

An RFID tag simulator based on the Atmel AT91SAM7S64 micro–controller

A tag simulator is a device that can exchange data with an RFID reader in the same way as a real transponder. It may be of help for reader developers in the process of testing the device response and adjusting the communication algorithms. It may equally help system integrators in testing and tuning the performance of the complete RFID system that comprises the readers, the network to which they are connected and the database. The simulator described here is based on the Atmel AT91SAM7S64 micro-controller and covers the “transponder talk first” protocols of full duplex and half duplex types for the carrier frequencies of 125 KHz and 134.2 KHz. The simulator is a PC-configurable stand-alone device.

A Low Cost Anticollision Reader

The chapter presents some aspects related to the design of a low cost anticollision reader based on the HTRC110 reader chip from NXP Semiconductors (NXP Semiconductors, 2006 a) and the AT91SAM7S64 controller from Atmel. The HTRC110 reader chip was mainly intended for integration into systems that need to identify one single RFID tag at a time. At the request of the host the chip sends the adequate command to the tag, retrieves the answer of the latter in analog form, digitizes the data and offers to the host the data retrieved from the tag in binary format. The chip does not provide support for collision detection and anticollision identification procedures in case that several tags in the antenna field respond to the same command at the same time. Nevertheless, the chip does provide access to the analog demodulated signal representing the response sent by the tags via load modulation of the carrier. This access was meant by the producer for the purposes of antenna tuning and testing. In the present design, it is by exploiting this feature that one achieves the anticollision functions. In section 2 of the chapter one describes the general configuration of the reader at block level, and particularly how the internal ADC of the AT91SAM7S64 controller is used for converting the test signal of the HTRC110 chip to numeric format and what signal-processing procedures are used for extracting the bit information from the signal and detecting collisions on bit positions. Included is also a brief description of the communication facilities of the reader with a host PC, such as RS232, USB and wireless. In section 3 one addresses some aspects of the concern whether the analog signal provided by the HTRC110 chip is adequate enough for collision detection. The main point here is that, while the other members of the anticollision readers produced by Frosch Electronics use constant amplitude current drive for the antenna and they decode the antenna voltage variations caused by load modulation at the tag, in the present case the HTRC110 chip uses constant amplitude voltage drive and it decodes the voltage variations at the junction between the antenna coil and the tuning capacitor. Because of this, the load modulation employed by the tag causes transients in the reader antenna that are longer than in the current drive case and are directly influenced by the antenna Q. In turn these transients cause the demodulated signal from the tag to have slower raising/falling edges than in the current drive case, which may interfere with collision detection if these transients are too long. It is the purpose of the section to analyze the dependence on Q of this effect and to compare it with the current driven case.

An RFID Reader Based on the Atmel AT91SAM7S64 Micro-Controller

Retrieving data from transponders that are located at the same time inside a certain area is one of the RFID applications that the gaming industry is interested in. The RFID reader currently produced by Gaming Partners International is aimed at such application. An international cooperation project funded by the named corporation had as target the development of a reader intended to upgrade the existing one. We explain in the following why the decision to use the AT91SAM7S64 microcontroller for the new design translated into benefits in terms of reliability, speed, higher integration and easier development and maintenance

Besov regularization, thresholding and wavelets for smoothing data

Smoothing of data is a problem very important for many applications ranging from 1-D signals (e.g., speech) to 2-D and 3-D signals (e.g., images). Many methods exist in the literature for facing the problem; in the present paper we point our attention on regularization. We shall treat regularization methods in a general framework which is well suited for wavelet analysis; in particular we shall investigate on the relation existing between thresholding methods and regularization. We shall also introduce a new regularization method (Besov regularization), which includes some known regularization and thresholding methods as particular cases. Numerical experiments based on some test problems will be performed in order to compare the performance of some methods of smoothing data. AMS (MOS) Subject Classifications: 65R30, 41A60.

Automated platform for determination of LEDs spatial radiation pattern

Nowadays technologies lead to remarkable properties of the light-emitting diodes (LEDs), making them attractive for more and more applications, such as: interior and exterior lighting, outdoor LED panels, traffic signals, automotive (tail and brake lights, backlighting in dashboard and switches), backlighting of display panels, LCD displays, symbols on switches, keyboards, graphic boards and measuring scales. Usually, LEDs are small light sources consisting of a chip placed into a package, which may bring additional optics to this encapsulated ensemble, resulting in a less or more complex spatial distribution of the light intensity, with particular radiation patterns. This paper presents an automated platform designed to allow a quick and accurate determination of the spatial radiation patterns of LEDs encapsulated in various packages. Keywords: LED, luminous

Test and measurement procedures for RFID systems

The necessity of having instruments for analyzing the quality of signal received by the reader from the transponder is more and more important in order to evaluate the performance parameters of RFID systems. In this paper we review the existing test procedures and transponder simulators that proved their utility in the development of SLRM1000 RFID system. We propose a new measurement device and procedure that produce 2D maps of the quality of the received signal as the position of the transponder is varied across the antenna.

Automated Platform for Characterization of RFID Reader Antennas

RFID systems have evolved from simple ones to complex equipment, but one of the most important components in their structure is the antenna. The overall system performance is highly depending on quality of the communication between antenna and transponders, so it is very important to characterize it with high accuracy. This paper presents an automated platform for antenna characterization based on automatic exploration of the usable area of antenna, using a transponder positioned on X and Y coordinates with two stepper motors and the associated mechanics.

RFID Readers for the HDX Protocol - A Designer’s Perspective

Previous work (Gelinotte et al., 2006; Vuza et al., 2007; Vuza et al., 2009) presented the contribution of the present authors to the development of readers for communication with tags according to the FDX protocol. Readers produced so far by Frosch Electronics were classified as voltage-driven and current-driven (Vuza et al., 2009), according to which circuit variable is controlled by the reader and which is controlled by the tag (and sensed by the reader). A voltage-driven reader powers the antenna with an AC voltage of constant amplitude. The FDX tag transmits data by load modulation, which causes the variation of the voltage at the tap point (the junction between the antenna coil and the tuning capacitor). The reader senses the latter voltage and extracts the baseband signal that contains the data. A current-driven reader powers the antenna with an AC current of constant amplitude. Again, the FDX tag transmits data by load modulation, which this time modulates the voltage across the whole antenna circuit. The reader extracts the data from the latter voltage, the tap point connection being not needed in this case. Recently, Frosch Electronics decided to add a new feature to the existing readers, providing them with the possibility of communicating with tags that use the HDX protocol, of interest in applications such as animal identification, so that the same reader could cover a larger variety of applications. In FDX, the tag is continuously powered by the reader. In HDX, the tag is first charged by an RF pulse of limited duration from the reader, and then it transmits the data using the energy stored during the first step, by driving its coil with an AC voltage whose frequency toggles between two values fC = 134.2 KHz and fLOW = 123.7 KHz prescribed by the HDX standard. After a brief reminder on the two types of FDX readers in section 2, we present in sections 3 and 6 circuit topologies achieving the HDX extension for each of the mentioned classes of readers. The topologies are different for the two classes according to whether the tap point is accessible or not. For voltage-driven readers, the schematic is based on the usage of the TMS3705 circuit as a bit decoder. For current-driven readers, we consider the option of bit decoding by either a dedicated IC or by building a custom decoder from discrete hardware components supplemented by a software component, which could in principle offer more control over the decoding process. In section 4 we discuss the important issue of transients, which has to be taken into account when striving for data integrity, and hence reliability. Transient effects have been discussed

An RFID tag simulator for the FDX and HDX protocols

A tag simulator is a device that can exchange data with an RFID reader in the same way as a real transponder. It may be of help for reader developers in the process of testing the device response and adjusting the communication algorithms. It may equally help system integrators in testing and tuning the performance of the complete RFID system that comprises the readers, the network to which they are connected and the database. The simulator described here is based on the Atmel AT91SAM7S64 micro-controller and covers the “transponder talk first” protocols of full duplex (FDX) and half duplex (HDX) types for the carrier frequencies of 125 KHz and 134.2 KHz.

Platform for monitoring the temperature of power LED junction by using the embedded protection diode

The junction operating temperature of a power LED can be estimated by measuring with a thermocouple the temperature of the closest accessible metal part of the LED package, which is in most of the cases one of the electrical terminals, and making a calculation by taking into consideration the thermal resistances of the materials included in the LED structure. In the situations where the electrical terminals are not accessible, being placed right under the LED package, the thermocouple could be placed on the mounting PCB used heatsink, as close as possible to the thermal pad of the LED, but this may introduce errors, making the temperature estimation not accurate. The junction operating temperature can also be estimated by measuring the forward voltage of the LED, knowing the temperature coefficient of the forward voltage. In this paper the authors proposed an innovative method for measuring the operating temperature of power LEDs, using as temperature sensor the protection reverse diode embedded in the LED package.