Tracking head motion for the crosshairs for most FPS is a challange. For this we will need to use optics to create a high and low resistence. this is accomplished with very few componants. The only issue is range the optics will need to be fairly close I think we can fix this by using better IR leds in an array.
Here is the proof of concep of head tracking motion..
Here is the diagram for wiring.
(https://www.acidmods.com/tutorials/headtracking/headtracking.jpg)
Setting up the optics is sooooo simple very cheap to make just need to order some parts from mouser.
Here is the parts
1: Quantity 2 of TSL262R-LF (http://www.mouser.com/Search/ProductDetail.aspx?qs=FbAvI%252bwzkvxzjWK78dp2yg%3d%3d)
2: Quantity 2 of TSL12S-LF (http://www.mouser.com/Search/ProductDetail.aspx?qs=ck8ERu4TygdFXGB8JByQYw%3d%3d)
Here is how I have the test POC set up..
(https://www.acidmods.com/tutorials/headtracking/headtracking1.jpg)
(https://www.acidmods.com/tutorials/headtracking/sensor.jpg)