TurboCNC requires a 1/rev spinder indexing puls pulse to enable it to sync Z axis motion to the spindle for threading.
Dave K, the author of TurboCNC, provided a simple circuit to amplify the signal from the optical gate. I laid out this circuit on a prototype board as shown in the attached pdf. This board is housed in a small box mounted on the side of the motor speed controller.
The target is a simple Aluminium disk with a tab of greater radius than the rest to cut the beam in the optical gate.
An easier solution would be to use the Sharp GP1A05 or similar which have the amp and a schmidt trigger integrated into the optical gate housing.