I plan to build an RFID system with a wireless sensor network that could monitor traffic inside spacious bus stations, and that could inform administrators about whether a particular bus was arriving on time, early or late. This information would be displayed on various wireless displays inside and outside the station. I intend to keep RFID readers inside buses to identify stops (the stops would have tags). Transceivers, ZigBee-based or otherwise, would send data to other transceivers on nearby buses, and this information would ultimately be forwarded to a central station. Which type of reader (range and frequency) could best be kept inside buses to identify tags at stops? And which type of transceiver (range and frequency) would best be kept inside the vehicles to transmit and receive data? I need to know the reception range of such readers, their respective cost and where I can obtain them. Thank you so much.
I would suggest that you do not create a wireless sensor network that sends data from one node to another. This would be difficult to achieve with buses on roads, as the range of wireless sensors (or “motes”) is short. Rather, I would recommend you install a passive ultrahigh-frequency (UHF) reader inside each bus, with an antenna protected from the weather on the side that would face the bus stops. The read range of a passive UHF reader is about 20 to 25 feet (it could be more or less depending on the tag used, as well as the environment and the reader’s quality). The interrogator would need to be linked to a cellular device in order for it to transmit read data to a central server.
I would then place tags on the bus stops, thereby ensuring that they are within 18 to 20 feet of the RFID reader antenna installed on the vehicles. I would also place tags at the depot’s entrance, and at parking locations within the depot and in other key areas. Each tag contains a unique ID number, which can be associated with a specific location. Each time the reader on bus 1 read a tag, for instance, that information would be sent to the central server, which would transmit that information to those who need it. So if the bus were to pass a stop at the corner of Main Street and Constitution Ave., for example, the tag would be read, the ID would be sent to the server and managers would know the bus was at that stop. If the bus entered the depot, a tag would be read at the entrance and managers would know the bus was arriving.
If you want to get a little more out of the system, you could create software to estimate the time at which a bus will arrive at each stop and at the depot. This can be accomplished by calculating the amount of time it takes to travel from one stop to another. If there is heavy traffic, if the bus is traveling at an average speed of 20 miles per hour, and if the next stop is located one mile away, you could estimate that it would take about three minutes to arrive at the next stop.
You can purchase readers on the Internet from various websites, such as the Atlas RFID Store.
—Mark Roberti, Founder and Editor, RFID Journal
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