초록 ▼

A method and apparatus for conditioning an input signal from an optical detector includes a controller for dynamically modifying adjustable delay elements connected to the input signal, thereby modifying characteristics of the signal conditioning circuitry. The method and apparatus determines the tr

A method and apparatus for conditioning an input signal from an optical detector includes a controller for dynamically modifying adjustable delay elements connected to the input signal, thereby modifying characteristics of the signal conditioning circuitry. The method and apparatus determines the transitions between binary levels of an input signal such as a scanned bar code label by detecting zero crossings of an approximated second derivative of the input signal. Samples of the input signal are obtained by using delay lines, sample-and-hold circuits, an analog shift register or similar device. The first derivative of the signal is approximated by the slope of a straight line between two sampled points on the waveform. The second derivative is approximated by the difference between two first derivatives. Zero crossings of the second derivative indicating transitions of the input signal may be determined either by detecting a signal peak on both sides of the zero crossing, or by comparing the second derivative signal to zero when the first derivative exceeds a positive or negative threshold. The amount of shift in the zero crossings may be estimated by measuring relative amplitudes or widths of the surrounding signal lobes. The time between sample points may be adjusted to match a particular range setting of a scanner having a plurality of range settings.

대표청구항 ▼

[ What is claimed is:] [1.] An apparatus for reading encoded images comprisinga symbol reader having a variable focusing distance, said symbol reader comprising an optical detector generating an electrical input signal having an amplitude varying over time in response to an amount of detected light,

[ What is claimed is:] [1.] An apparatus for reading encoded images comprisinga symbol reader having a variable focusing distance, said symbol reader comprising an optical detector generating an electrical input signal having an amplitude varying over time in response to an amount of detected light,means for conditioning said input signal and generating a conditioned signal thereby, andmeans for dynamically modifying electrical characteristics of said means for conditioning in response to changing said variable focusing distance.