This code can be used on the LC and 4.0 but they need a level translator if connected to a 5 volt touchpad.
The Touchpad_3p2.ino code sets up the touchpad to be in remote mode so that the Teensy can poll it after finishing the keyboard scan. 
The Touchpad_Stream_mode.ino code sets up the touchpad to be in Stream Mode so it sends data when ever it detects finger movement.
ADB_Trackball.ino will read an Apple Data Bus trackball and send the results as USB mouse commands. 
I2C_Touchpad.ino is an example routine to read a basic touchpad over an I2C bus and send the results as USB mouse commands. 
Read the comments at the beginning of the code to see the address and register numbers for this example touchpad.
Azoteq_TP.ino uses the Teensy I2C pins to read an Azoteq TPS65-201A-S touchpad and send the relative X/Y movement
and the finger-tap as USB mouse commands. For more information on the registers, read the Azoteq data sheet at:
https://www.azoteq.com/images/stories/pdf/iqs5xx-b000_trackpad_datasheet.pdf

For a complete description of how to interface a Teensy to a touchpad, read my touchpad guide at: 
https://www.hackster.io/frank-adams/laptop-touchpad-conversion-to-usb-d70519