Optical Eye Tracker
An optical eye tracker is a device used to track the position and movement of eyes generally with reference to head. The movement of the eyes can be tracked on a TV monitor with the help of cursor. The basic principle behind this device is based on the properties of light. As per the law, whenever light rays fall over an object, they are either reflected or absorbed. The amount of light reflected or absorbed depends on the physical properties of the object. Here, the object under consideration is human eye. The focus is laid on three parts of the eye that will respond to incoming light rays in different manner:
· The Sclera (the white portion of the eye)
· The Iris (the region bearing one’s eye color)
· The Pupil (the black entrance hole that serves as a light receptacle)
Each of the above mentioned parts reflects different amounts of light. The hardware for the system consists of two pairs of emitter-phototransistor mounted on the top of goggles/glasses. The emitter emits infrared light rays continuously which are detected by phototransistor. The amount of light falling at the detector depends on the parts of emitted light absorbed by portion of the eye on the axis. The voltage signal hence detected at the phototransistor is amplified and send to the STK500 microcontroller board at port A for analog to digital conversion. Next is the software control for the circuit and the hyper terminal. Software control covers the following points:
1. Converting signals from the two phototransistors
2. Controlling the movements of the cursors on the TV monitor
The hyper terminal is also an asset to the project as it helps in debugging the system.
Therefore, the Optical eye tracker is a wonderful bio-instrument which also adds on a healthy practical experience with electronics. It is designed keeping in mind the medical aspects of the IR emission.
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