Auto-Thresholding Tag Reader
Original Publication Date: 1985-Jul-01
Included in the Prior Art Database: 2005-Feb-18
This circuit eliminates misreads of identification tags due to varying contrasts in bar codes. The figure shows a bar code illuminated by L1 and focused by the lens on DET D2 through a slit S. D2 converts the focused image to photo current which is voltage converted in amplifier A1 . The signal at A1 output goes two ways: a) to the peak detector Q1 - C2 and its follower (FLWR) to the input of the comparator (COMP) through the resistive divider R9 - R10, and b) through the delay network R6-C3-R7 to the input of the comparator. The signal delay in R6-C3-R7 is chosen to be longer than that required to establish the switching threshold in the peak detector.