Transmissivity-coded data card systems

A reader for transmissivity-coded data cards each having a plurality of translucent digit representing areas the transmissivities of which correspond to the values of the digits represented and a translucent reference area, comprising:

• a plurality of light sources disposed to transilluminate corresponding ones of said areas when one of said cards is in a reading position;
• a plurality of photosensors disposed to receive light emerging from corresponding ones of said areas and to produce output currents proportional to the intensity of the received light;
• a plurality of operational amplifier means each receiving the output current of one of said sensors and producing an output voltage proportional to the magnitude of the received output current;
• reference voltage signal producing means for producing a plurality of reference voltage signals the magnitude of each of which is a predetermined fraction of the output voltage of the operational amplifier means which receives the output current of the photosensor disposed to receive light emerging from said reference area;
• and
• means for comparing the output voltages of the operational amplifier means receiving the output currents of the photosensors disposed to receive light emerging from digit representing areas with said reference voltage signals.

A transmissivity-coded data card system, comprising:

• a plurality of transmissivity-coded data cards each having a plurality of translucent digit representing areas the transmissivities of which correspond to the values of the digits represented and a translucent reference area;
• a plurality of light sources disposed to transilluminate corresponding ones of said areas when one of said cards is in a reading position;
• a plurality of photosensors disposed to receive light emerging from corresponding ones of said areas and to produce output currents proportional to the intensity of the received light;
• a plurality of operational amplifier means each receiving the output current of one of said photosensiors and producing an output voltage proportional to the magnitude of the received output current;
• reference voltage signal producing means for producing a plurality of reference voltage signals the magnitude of each of which is a predetermined fraction of the output voltage of the operational amplifier means which receives the output current of the photosensor disposed to receive light emerging from said reference area;
• and
• means for comparing the output voltages of the operational amplifier means receiving the output currents of the photosensors disposed to receive light emerging from digit representing areas with predetermined ones of said reference voltage signals.

A transmissivity-coded data card system, comprising:

• a plurality of transmissivity-coded data cards each having a plurality of translucent digit representing areas the transmissivities of which correspond to the values of the digits represented and a plurality of translucent reference areas;
• a plurality of light sources disposed to transilluminate corresponding ones of said areas when one of said cards is in a reading position;
• a plurality of photosensors disposed to receive light emerging from corresponding ones of said areas and to produce output currents proportional to the intensity of the received light;
• a plurality of operational amplifier means each receiving the output current of one of said photosensors and producing an output voltage proportional to the magnitude of the received output current;
• reference voltage signal producing means for producing a plurality of reference voltage signals the magnitude of each of which is a predetermined fraction of the output voltage of the operational amplifier means which receives the output current of the photosensor disposed to receive light emerging from the reference area having the highest transmissivity;
• and
• means for comparing the output voltages of the operational amplifier means receiving the output currents of the photosensors disposed to receive light emerging from digit representing areas with predetermined ones of said reference voltage signals.

A transmissivity-coded data card system, comprising:

• a plurality of transmissivity-coded data cards each having a plurality of translucent digit representing areas the transmissivities of which correspond to the values of the digits represented and a translucent reference area;
• a plurality of light sources disposed to transilluminate corresponding ones of said areas when one of said cards is in reading position in a reader;
• a plurality of photosensors disposed to receive light emerging from corresponding ones of said areas and to produce output currents proportional to the intensity of the received light;
• a plurality of operational amplifier means each receiving the output current of one of said photosensors and producing an output voltage proportional to the magnitude of the received output current;
• a tapped resistor connected across the output terminals of the operational amplifier means which receives the output current of the photosensor disposed to receive light emerging from said reference area for producing at its taps a plurality of reference voltage signals;
• and
• means for comparing the output voltages of the operational amplifier means receiving the output currents of the photosensors disposed to receive light emerging from digit representing areas with predetermined ones of said reference voltage signals.