My 88er roll reader, built in 1990, used 100 photo transistors in a tracker bar, read-out by a computer 7 bit-wise.  The light emitting diodes were regulated together by voltage, but the photo transistors were only once adjusted by selected resistors.

Now I made a new approach with fibre optics.  I use a plastic rod with drillings of 2.2 mm diameter to lead the optic fibres a few millimeters above the moving punched paper.  The other ends of the fibres end in photo transistors (infra red) with matching holes.  They are mounted on cards in a 19" card cage: 13 (14) cards each with 8 photo transistors, 2 voltage expanding gates and a 74LS245 IC to connect via flat cable to the card with a 8255 PIO in the computer.  The plastic rod was drilled 1/9" in line very precisely, thanks to Dr. Walter Tenten.  When I someday get a rod drilled with 110 holes of 2.2 mm diameter and 1/8" spacing distance, the 14th card will go to work for Welte T-100 red rolls.

At the visible card ends are trim-pots for the photo transistors.  Now the light emitting diodes under the roll are still regulated en bloc by voltage, but the photo transistors are tuned singly by trim-pots.  This way it is possible to read even the semi-translucent paper rolls of Dr. Juergen Hocker.

By the way, since the card cage unit uses its own 5- and 12-volt supply I damaged my computer when I switched it off and forgot to switch off the card unit before.  Now it runs on the monitor outlet and is switched off this way simultaneously.

Horst Mohr
Fri, 29 Jan 1999 19:52:56 MEZ

More articles by Horst Mohr are indexed at http://www.mmdigest.com/Archives/Authors/Aut248.html
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