I am currently working on a RFID tracking project. In short, I am using Arduino Mega 2560’s with an Adafruit Data Logger and Sparkfun XBee Shield with a Series 1 antenna to monitor a number of RFID 125 kHz antenna’s (via an antenna microchip). Hope that makes sense.
Currently, the Mega 2560 limits me to 4 Serial Hardware RX ports, I don’t require the TX ports. I am pretty sure the answer is no to my first question but I will ask anyway. Is there a way to expand the number of serial ports on the Mega 2560. In a perfect world, I require 40 RFID antenna’s per board, but even if I could double it to 8, I would be happy.
If not, can anyone recommend another solution that I could add to the Mega 2560? Or maybe another solution outside of the Mega 2560? In a perfect world, I would love to have the ability to put SD card and Xbee Antenna right onto the board, rather than stacking shields however, just having more serial ports for my UART antenna’s would be great!
In short, I have a series of small antenna’s sitting side by side. I would need to identify each antenna as well as the RFID tag.
What exactly in the RFID transmissions is important to you? Are you making a sort of 'phased array' RFID antenna? Where the signal arrives at multiple receivers but with a slight timing or phase delay. Or is receiving at each location independent of the others? Tell us more what the network of RFID stations is trying to accomplish. It might be an important design driving requirement.
While the Mega 2560 has enough i/o pins to do software serial with 40 RFID antenna board, I suspect you’ll get into trouble with a processing bottleneck if they are all talking at the same time. Even 8 might become an issue. Even with interupt driven software serial those bit will likely not be detected reliably.
As suggested in the other thread, I would consider making use of a small microprocessor per RFID node to translate serial to I2C. It can still be a bottleneck to get all the data on the central processor, but it will have all on the same bus and uniquely addressable. The microprocessor on the RFID node can then temporarily store the data until the bus is free. The micro will likely even have enough resources to keep track of time for a timestap to go with it if neccesary. But this depends on your answer on my first question up top.