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Remote Control Module for RFID Devices |
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Introduction
RFID implementations can be challenging and expensive. Usually RFID is just one part of the system and the interrogator (reader) needs to work in concert with other devices. For example, if you decide to use RFID to track real-time inventory on a conveyor line you will want to place an antenna under or above the belt. Soon however, you will realize that more than one antenna is needed to register transponders in different orientations. For that you will need a multiplexer that needs to be controlled separately via TTL levels and in sync with the reader. In addition, you will notice that running the device in scanning mode all the time may interfere with other equipment, or will eventually saturate the interrogator. To reduce the negative effects, you would place an optical eye on the conveyor and have the reader scan only when a carton is approaching. Based on the inventory reported by the RFID device, you may want to engage attenuators to redirect the flow of cartons to another shoot. Lastly, you may want to synchronize the dataflow with the input of your barcode scanner positioned close by. So, we end up with several hardware components that must work well together, where RFID is just one of the modules. The next challenge may seem trivial at first, but in large-scale deployments it becomes critical. This is the connection between the RFID device and the rest of the system. It is usually RS-232C (or alike), USB, etc. This is not good enough. The preferred way is an Ethernet (perhaps even wireless) connection for its ease of configuration, speed and scalability. Running RS-232C cables to each reader often is not an option. Bridge solutions are available in the form of Serial-to-TCP converters, however they too have their limitations. One of them is that the host computer needs to be configured with additional software in order to work with the converter. There are a limited number of COM ports that can be used. The converters do not allow control of other hardware over the same interface (digital I/O, analog, etc.). Lastly, since they have no additional logic, the converters do not reduce the traffic and force the host computer to handle all low-level requests for each device. Having an individual PC per reader is too expensive. DataBrokers, Inc. has developed a solution that addresses all of the above issues. Since the very beginning it was obvious to us that more a capable device is needed to control the RFID and other hardware, including being programmable and able to execute its own software as needed. In addition, this device had to have Ethernet interface to bridge the gap and make the system flexible. PC would have worked, except the prohibitive cost and the problem of its moving parts. We did not want to have a component that takes time to start, or could be damaged if the power is lost. The ideal solution came in the form of a solid-state microprocessor module with a number of digital I/O ports and TCP/IP stack. Hence, we developed the RCRFID module and the embedded software that goes with it. It has the best of both worlds because it is inexpensive, reliable, low maintenance and at the same time it is programmable. This device provides all necessary interfaces, has low power consumption, contains no moving parts and does not require special cooling. Description The Remote Control RFID module is a smart 8-bit embedded microprocessor that takes on the task to control remote RFID readers and systems. It is a design based on the popular Rabbit 3000 processor from Rabbit Semiconductors. The firmware implements a special protocol that allows a remote PC to control the attached RFID reader in conjunction with a multiplexer (MUX). The current implementation (RCRFID-1B) can control an attached array of 9 multiplexer devices (arranged in a master-slave configuration with 8 antennas each), which provides for the control of 64 antennas from one RFID reader. If no MUX control is required, there are 6 digital outputs that can be used for control of external hardware. If only up to 8 antennas are used, 3 outputs can control one MUX and the other 3 can be used to control external hardware. The digital outputs are optically isolated. There is the capability to have 2 separate and isolated power supplies in the RCRFID module that can provide power to the microprocessor and to an external device if required. There are 2 general-purpose digital inputs. There is the capability for many more if necessary. The Rabbit 3000 is a flexible solution and offers a total of 52 digital I/O and 6 serial ports (shared pins). Currently 3 of the serial ports are used. One for programming, one for setup/control and one for the RFID reader. A number of external devices can be attached and controlled from the RCRFID module per user request with a simple upgrade of the firmware. In some cases a modification or additional hardware may be required to accommodate the interfacing of the external hardware. |
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