▁nearly ▁all ▁bar code ▁readers ▁contain ▁dec oder ▁circuit ry ▁that ▁can ▁analyze ▁the ▁bar code ' s ▁image ▁data ▁provided ▁by ▁the ▁sensor ▁and ▁sending ▁the ▁bar code ' s ▁content ▁to ▁the ▁sc anner ' s ▁output ▁port . ▁ ▁Types ▁of ▁bar code ▁sc ann ers ▁ ▁Technology ▁▁ ▁Bar code ▁readers ▁can ▁be ▁differenti ated ▁by ▁techn ologies ▁as ▁follows : ▁ ▁Pen - type ▁readers ▁ ▁Pen - type ▁readers ▁consist ▁of ▁a ▁light ▁source ▁and ▁phot odi ode ▁that ▁are ▁placed ▁next ▁to ▁each ▁other ▁in ▁the ▁tip ▁of ▁a ▁pen . ▁To ▁read ▁a ▁bar code , ▁the ▁person ▁holding ▁the ▁pen ▁must ▁move ▁the ▁tip ▁of ▁it ▁across ▁the ▁bars ▁at ▁a ▁relatively ▁uniform ▁speed . ▁The ▁phot odi ode ▁measures ▁the ▁intensity ▁of ▁the ▁light ▁reflected ▁back ▁from ▁the ▁light ▁source ▁as ▁the ▁tip ▁cross es ▁each ▁bar ▁and ▁space ▁in ▁the ▁printed ▁code . ▁The ▁phot odi ode ▁generates ▁a ▁wave form ▁that ▁is ▁used ▁to ▁measure ▁the ▁width s ▁of ▁the ▁bars ▁and ▁spaces ▁in ▁the ▁bar code . ▁Dark ▁bars ▁in ▁the ▁bar code ▁abs orb ▁light ▁and ▁white ▁spaces ▁reflect ▁light ▁so ▁that ▁the ▁voltage ▁wave form ▁generated ▁by ▁the ▁phot odi ode ▁is ▁a ▁representation ▁of ▁the ▁bar ▁and ▁space ▁pattern ▁in ▁the ▁bar code . ▁This ▁wave form ▁is ▁dec oded ▁by ▁the ▁sc anner ▁in ▁a ▁manner ▁similar ▁to ▁the ▁way ▁Mor se ▁code ▁d ots ▁and ▁dash es ▁are ▁dec oded . ▁ ▁Las er ▁sc