I'm almost a beginner to microcontrollers and have done a few simple projects, but this time I have to use an Arduino Uno (powered by a battery) to support an RFID reader (RC522), a Zigbee module and a touch screen altogether. Apparently there are too few pins to support all the modules. What is the easiest way to implement such a system?
Also I don't know what the RFID, zigbee and touch screen uses (generic GPIO pins, I2C, SPI, something else)?
You always can combine multiple inputs/outputs using a multiplexer (i.e. 74HC165, 74HC595), although it will mean extra software and less performance.
About the touch screen, that might be problematic regarding performance and memory usage, since the Uno has only a few KB and even the more expensive Arduino's do not have that much memory you might need.