Read from multiple input devices
One of the cool features of USB is that using Human Interface Device (HID) you can get a new device to behave as, for example, a keyboard. You can do this now with a Teensy or an Arduino UNO (but not the FTDI-based older Arduino boards). The key is that by using the proper USB messages a device can talk to the system in a way that looks like a mouse, a keyboard, etc. The good thing about talking like a keyboard is that applications that expect a keyboard input may be fed directly with the data from that device. This many times the case with devices like a barcode reader, that can input the scanned code to the application software as if the user was typing that number on the corresponding box of the program, which is convenient just in case the code is unreadable for any reason by the reader but not by the user (or if the barcode scanner is broken or stolen). My current project required reading RFID codes and for that I already bought a RFID reader with I2C interface that could be