Fat bit bar code reader

Abstract

A reader for reading bar code symbols containing so called 'fat bits' arranged on exposed film is described. A strip of film 10 which has one or more frames 11 has a boundary edge 13 with space in which zero, one, or two fat bits 14 is provided for each frame 11. A light source 28 directs light through the boundary edge 13 of the strip 10. A pair of optical sensors 25, 27 receives the light directed through the boundary edge 13. The sensors 25, 27 each output a signal corresponding to the presence or absence of a fat bit to a detector circuit 220. The detector circuit 220 outputs a signal corresponding to the fat bit to a controller 250 as the strip moves between the light source 28 and the sensors 25, 27. An encoder 230 measures the displacement of the strip 10 as it moves, and outputs pulse signals to the controller 250 representative of units of strip 10 displacement. The controller 250, while receiving the output from the detector circuit 220, measures the width of the fat bit 14 by translating the pulse signals from the encoder 230 into signals representative of the width of the fat bit. The presence of valid fat bits is then verified where the measured width of the fat bits is within a certain range indicative of a valid fat bit. The reader also reads the DX code 12 for each frame 11 on edge 13 by outputting signals from the pair of optical sensors 25, 26 to the detector circuit 220 representative of received light directed through the boundary edge 13 corresponding to the DX code 12 bits. The controller 250 then measures the width of each DX code 12 bit in the same manner as fat bits 14 using the pulse signals from encoder 230 while receiving from the detector circuit 220 output indicative of a DX code 12 bit. The measured DX code 12 bit widths are then stored in controller 250 for later decoding. Sensors 25 and 26 are spaced from each other to optimize reading of DX code 12, while sensors 25 and 27 are spaced from each other by less than the minimum width of a fat bit 14. The width of the fat bit 14 is substantially greater than the width of bars representing DX code 12 bits.