| 摘要 |
<p>The infra-red bar code reader has an infra red LED and two photo transistors mounted vertically one above the other with a dividing wall between them for a distance of 45mm forward of their front face. An optical lens is placed at this distance from the optical devices, making the emitted light rays near parallel in the horizontal plane with a small divergence angle, and focussing the reflected rays onto the photo transistors. Bar codes comprising non-reflecting areas alternating with reflecting areas, give variable reflected illumination at the phototransistors which are mounted one above the other below the light emitting diode. An electrode circuit scans the outputs from these phototransistors and passes the signal through a filter, a Schmitt trigger circuit, and a pulse stretching circuit.</p> |
