Dual edge detector for bar codes

DETAILED DESCRIPTION What is claimed is: 1.
A method of reading biphase modulated bar codes by detecting leading and trailing edges of bar signals occurring in an information signal generated by an optical sensor, which comprises: a.
attenuating high and low frequency noise and uniformly shaping said information signal; b.
differentiating said information signal to further remove low frequency noise, and to form a bipolar waveform for both leading and trailing edge detection of said bar signals; c.
separating and integrating positive and negative half-waves of said bipolar waveform to substantially remove the effects of intersymbol interferences which may occur from the sensing of adjacent bars in a bar encoded data field; d.
comparing integrals of said positive and said negative half-waves with a reference amplitude to detect one of said bar signals; e.
forming a digital synchronization waveform from said bipolar waveform to define a continuous train of bar time periods; f.
signaling the occurrence of a zero-crossing in a positive to negative transition of said bipolar waveform; and g.
when the amplitude of one of said integrals equals said reference amplitude, correlating the time of occurrence of said zero-crossing with said digital synchronization waveform to identify the half period position of said one of said bar signals within one of said continuous train of bar time periods.
2.
The method set forth in claim 1, including the step of signaling the presence of said one of said bar signals in a trailing half period of said one of said continuous train of bar time periods.
3.
The method set forth in claim 1, wherein the step of forming a digital synchronization waveform from said bipolar waveform includes the steps of: a.
detecting a plurality of waveform peaks in said bipolar waveform; b.
generating a pulse train normalized in both amplitude and width upon detecting said plurality of waveform peaks; c.
generating an analog waveform in response to said pulse train, said analog waveform having a frequency twice that of said information signal to accommodate the reading of biphase modulated bar codes; and d