It is important that you follow these instructions as it is not a good idea to have two different ApplePS2Controller.kexts under different names. Originally the Voodoo code was packaged as ApplePS2Controller.kext as it was based on code originally from Apple. Newer versions, including this one, are called VoodooPS2Controller.kext. So ApplePS2Controller.kext must be removed if you previously installed it.

In addition, as of version 1.7.4, AppleACPIPS2Nub.kext is integrated into VoodooPS2Controller.kext, and you must remove it (if you previously had one of those versions installed).

Also, do not use VoodooPS2Controller.kext and AppleSmartPS2TouchPad.kext together.

Removing incompatible kexts from /S/L/E:

sudo rm -rf /System/Library/Extensions/AppleACPIPS2Nub.kext
sudo rm -rf /System/Library/Extensions/ApplePS2Controller.kext
sudo rm -rf /System/Library/Extensions/ApplePS2SmartTouchPad.kext

Removing incompatible kexts from /L/E:

sudo rm -rf /Library/Extensions/AppleACPIPS2Nub.kext
sudo rm -rf /Library/Extensions/ApplePS2Controller.kext
sudo rm -rf /Library/Extensions/ApplePS2SmartTouchPad.kext

Installing VoodooPS2Controller.kext (10.11 and later):

cd directory-to-where-your-unzipped-download-is
sudo cp -R Release/VoodooPS2Controller.kext /Library/Extensions

Installing VoodooPS2Controller.kext (prior to 10.11):

cd directory-to-where-your-unzipped-download-is
sudo cp -R Release/VoodooPS2Controller.kext /System/Library/Extensions

Rebuild kernel cache:

sudo touch /System/Library/Extensions && sudo kextcache -u /

Then reboot your system.