RESUMO
The designed EOG switch was based on the principle of the detection of the saccadal velocity producing a pulse above a certain selected value of the saccadal derivative. The EOG transducer is preferable above an eye switch designed on the infrared limbus-pupil reflection method because of two reasons, namely in its use for vertical eye movements and because of its low costs when composed with operational amplifiers (741) or with IC's. AC-coupling between the differential amplifier and the main amplifier excludes the effects of the well-known DC-drift during EOG recording on switching. An optocoupler at the output of the switch serves for the safety of the non-vocal handicapped during the communication process with the Handiwriter. Experience is obtained with the EOG switch connected with the Handiwriter system by one quadriplegic CVA patient and one quadriplegic ALS patient. A possible group of patients as candidates for using the EOG switch has been indicated in the discussion.
