| 摘要 |
PROBLEM TO BE SOLVED: To provide a device with adjustment elements and to improve the reliability of the entire device relatively inexpensively by detecting the difference between a detection signal and a delay signal to set a proper threshold. SOLUTION: When a boundary part of a variable density of a bar code passes a slit 5, the output of a reflection photo sensor 1 is linearly changed to become the detection signal having a trapezoidal waveform, and the signal passes a delay circuit 3 to become the delay signal having a trapezoidal waveform. A difference signal generation circuit 5A shows a difference signal between the detection signal and the delay signal, and it is processed by a comparison circuit 4B to output an output signal. Since the difference signal between the detection signal and the delay signal is used to set a proper threshold in this manner, the bar code can be read without an influence of the sensitivity of the inexpensive photo sensor 1, and a bar code reader is obtained which is not required to adjust the threshold for the change of the reflectivity of a read object card or the variance of the moving speed and has a simple constitution and a high reliability. |
