Detector arrangement for data-card readers

Claim 1

A card reader for reading cards marked either by holes or by writing and providing an output indicative not only of the presence or absence of a mark but of the type of mark as well, the card reader comprising: a light source emitting light toward a principal surface of a card to be read; a reflective surface having a reflective power greater then that of the unmarked surface of the card and located parallel to an opposite surface of the card, for reflecting light reaching the reflective surface via a hole in the card back through the hole; an optical detector for receiving light of a first intensity reflected from marks indicated by writing on the card, light of a second intensity greater than the first reflected from the unmarked surface of the card, and light of a third intensity greater than the second reflected from the reflective surface through marks indicated by holes in the card, and for producing a sense signal whose amplitude is indicative of the amount of light reaching the optical detector; and level detection means coupled to the sense signal for producing an output signal having three distinct values respectively indicative of the presence of a mark produced by a hole, the presence of a mark produced by writing, and the absence of a mark.