CP/PC364 Data Communications and Networks Laboratory

Serial RFID Reader (UART)

Overview

This week's laboratory investigates RS-232 (or EIA 232) communication.

Background

A simple example of a serial device is an RFID reader, since it only requires communication in one direction. Since you've already used the Arduino built-in UART, RS-232 communications with the RFID reader should be straightforward. One of the limitations of the Arduino is that if two devices need serial communication, there is a problem. Fortunately, there is a SoftwareSerial library that allows a UART to be simulated on other pins. You'll use this for the RFID reader since you still need to connect to the console. Note: The RFID reader is designed for "TTL serial" operation, which means its pins will be at TTL levels, not at acceptable RS-232 levels. Since the UART pins on the Arduino are also at TTL levels, this makes the interfacing simpler than it would be otherwise.

Objectives

1. Become familiar with real serial communication using the SoftwareSerial library emulating a UART with an external device.

Equipment

• Arduino Uno board, with LCD display
• RFID reader and tags

Exercise

1. Look at one of the SoftwareSerial examples and figure out how to set up pins to use for this purpose. The comments at the beginning of the sketch should indicate pins that can be used. Choose two for the software UART and connect them together as in the previous exercise. Modify your previous sketch to send characters out the TX and in the RX pins and echo the received characters to the LCD display. This should be a pretty minor modification to the previous sketch.
2. Questions to ask before you start (Consult the data sheet to answer these.):
   1. What Arduino pins will you use for the software serial port?
   2. What baud rate does the RFID reader use? How many data and stop bits?
   3. What pin has data coming out of the RFID reader? Does that need to go into the TxD or RxD pin on the Arduino? In other words, when connecting to serial devices, do TxD and RxD of both match, or do they reverse?
3. Connect the Arduino to the RFID reader. Notice there is an additional signal input to the RFID reader that you can simply jumper to power or ground as appropriate to start.
4. Use one of the SoftwareSerial examples to repeatedly read characters from the pin you've chosen for the software UART. Send the characters to the hardware UART. You can use the serial monitor to test this and see that it works.
5. Once you have it working, create a sketch that incorporates the LCD software as well so you can display the RFID information to the LCD display instead of to the hardware UART. It would be good to use an output pin of the Arduino to replace the jumper above, so that the RFID operation is totally handled by the sketch.

Demonstrate and explain your results to the lab instructor