Design of a Light Activated Switch for Persons with Cerebral Palsy

A light activated switch for persons to operate switch-controlled computer software or other communication device has been developed. A light emitting diode is attached to the user’s forehead. An array of photo transistors is mounted at a fixed position from the body. It requires a small but controllable motion to activate the switch by aiming the LED beam at the target area of the receiver. The false activation due to uncontrollable motion will be a problem associated with cerebral palsy. The LED in the transmitter is driven by oscillator at 1 kHz and the band pass filter which is in receiver is tuned at that frequency¹. The level of received is detected by an amplitude demodulator once the signal is filtered. When the signals amplitude reach’s the threshold, a one short timer is triggered which then latches the switch for predetermined period. The system was tested by an 8 year old child and has demonstrated a satisfactory result. The sensivity and specificity are important factors for reliable operation of the light activated switch associated with the cerebral palsy.⁶