Method of and apparatus for electronic scanning

A method of controlling a scanning luminous barrier system comprising

• providing a series of electro-luminescent diodes, and associating a series of phototransistors respectively with said electro-luminescent diodes,
• triggering said diodes in sequence to emit a light pulse, and simultaneously triggering the associated phototransistors in sequence to enable the phototransistors to sense a light pulse,
• reflecting the light pulse from each diode to its associated phototransistor for detection,
• simultaneously pulsing a multi state switching circuit and a multi state comparison circuit,
• triggering said diodes and phototransistors in response to the state of said switching circuit,
• providing a first control step, said first control step including comparing the state of the switching circuit with the state of the comparison circuit to determine agreement between the states of these circuits and continuing triggering of the electro-luminescent diodes and phototransistors only upon a condition of agreement of the states of the switching circuit and comparison circuit,
• providing a second control step, said second control step including monitoring signals indicating reception of light pulses by the phototransistors and stopping the scanning if the signal monitored indicates reception of light pulses by the phototransistors during a time period in which said diodes are not to be triggered,
• providing a third control step, said third control step including changing the state of said switching circuit during a time period in which said diodes are not to be triggered while maintaining the state of the comparison circuit and continuing the scanning only if there is disagreement between the levels of the comparison circuit and the switching circuit, and
• providing a fourth control step, said fourth control step including monitoring the level of the light pulses sensed at the phototransistors, providing an indication of signal from the phototransistors only if the level monitored is within a predetermined range of levels, and stopping sequencing in the absence of indication of signal from the phototransistors.