Here is a custom version of LIFA to implement quadrature encoders using an Arduino encoder library (v1.1). I've included a diff file named LabVIEWInterface.ino.diff in unified diff format which shows the parts that have been changed.
How to Use
If you are not currently using a custom firmware, you simply need to upload this custom firmware instead.
Can only implement a single quadrature encoder on pins 2 and 3. Hook up the A and B channels to these pins.
Arduino Mega 2560:
Two encoders implemented by default. Encoder 0 is on pins 2 and 3 and encoder 1 is on pins 18 and 19.
A third encoder may be enabled by uncommenting "// #define ENCODER_OVERRIDE_TWI" (removing the //) and then re-uploading. If enabled, the two wire interface (TWI) cannot be used. This includes the I2C protocol. The third encoder is encoder 2 on pins 20 and 21.
I've tested encoders 2 and 3 an the Arduino Mega 2560 successfully. Encoder 0 did not seem to work on my Mega for some reason but I have used it in the past successfully on this same Mega. I do not currently have an Arduino Uno to test. A US Digital S4-360-250-N-S-B was used.
Please let me know your results and any feedback is appreciated. Thanks.