Adaptive threshold optical reader

• US 4,230,265 A
• Filed: 05/07/1979
• Issued: 10/28/1980
• Est. Priority Date: 05/07/1979
• Status: Expired due to Term

• Current Assignee: Citicorp Development Center Incorporated (Citigroup Incorporated)
• Original Assignee: Transaction Technologies Incorporated (Citigroup Incorporated)
• Inventors: Casaly, Richard J.
• Primary Examiner(s): Cook, Daryl W.
• Application Number:
  US06/036,686
• Time in Patent Office: 540 Days
• Field of Search: 235/454, 235/455, 235/458, 235/459, 235/462, 235/463, 340/146.3 AG, 250/555
• US Class Current: 235/455
• CPC Class Codes: G06K 7/10851 Circuits for pulse shaping, amplifying, eliminating noise signals, checking the function of the sensing device basic electronic circuitry H03
• CPC Class Codes: G06K 7/14 using light without selection of wavelength, e.g. sensing reflected white light G06K7/10831 - G06K7/1097 take precedence

Abstract

An adaptive threshold optical reader for detecting optically encoded information when positioned within an optical path, including a light source for producing light energy along the optical path, a light detector responsive to the light energy along the optical path and for producing an ouput signal in accordance with the light energy detected by the light detector, means responsive to the output signal from the light detector and with the means having at least two states and with the means in a first state producing an adaptive threshold signal when there is no optically encoded information positioned within the optical path and with the adaptive threshold signal representative of the output signal from the light detector with a threshold level of optically encoded information and adaptive to optical changes and with the means in a second state for producing an information signal representative of the output signal from the light detector when there is optically encoded information positioned within the optical path, means responsive to the adaptive threshold signal for storing the adaptive threshold signal, and means responsive to the stored adaptive threshold signal and the information signal for detecting the presence of optically encoded information in the information signal above a threshold level in accordance with the stored adaptive threshold signal.

Claims

1. An adaptive threshold optical reader for detecting optically encoded information when positioned within an optical path, including

a light source for producing light energy along the optical path,

a light detector responsive to the light energy along the optical path and for producing an output signal in accordance with the light energy detected by the light detector,

means responsive to the output signal from the light detector and with the means having at least two states and with the means in a first state producing an adaptive threshold signal when there is no optically encoded information positioned within the optical path and with the adaptive threshold signal representative of the output signal from the light detector with a threshold level of optically encoded information and adaptive to optical changes and with the means in a second state for producing an information signal representative of the output signal from the light detector when there is optically encoded information positioned within the optical path,

means responsive to the adaptive threshold signal for storing the adaptive threshold signal, and

means responsive to the stored adaptive threshold signal and the information signal for detecting the presence of optically encoded information in the information signal above a threshold level in accordance with the stored adaptive threshold signal.

2. The adaptive threshold optical reader of claim 1 wherein the means for storing the threshold signal provides for the storage on an analog basis.

3. The adaptive threshold optical reader of claim 1 wherein the means for storing the threshold signal provides for the storage on a digital basis.

4. The adaptive threshold optical reader of claim 1 wherein the information signal normally includes a first level representative of no optically encoded information and a second level representative of optically encoded information and with the adaptive threshold signal having a level between the first and second levels for the information signal.

5. The adaptive threshold optical reader of claim 1 wherein the means responsive to the output signal from the light detector has the signals produced during the two states controlled in accordance with different fixed resistance values.

6. The adaptive threshold optical reader of claim 5 wherein the different fixed resistance values are controlled in accordance with the presence or absence of optically encoded information positioned within the optical path.

7. The adaptive threshold optical reader of claim 1 wherein the means responsive to the output signal from the light detector has the signals produced during the two states controlled in accordance with resistance values provided by a variable resistor.

8. The adaptive threshold optical reader of claim 7 wherein the variable resistor is formed by a transistor whose absolute value of resistance is a logarithmic function of the current flowing through the transistor.

9. An adaptive optical card reader for detecting information optically encoded on a card and with the card reader including a card guide to position the card within an optical path, including

a light source for producing light energy along the optical path,

a light detector for detecting the light energy along the optical path and for producing an output signal in accordance with the intensity of the detected light energy,

means responsive to the output signal from the light detector for producing an adaptive threshold signal when there is no card positioned in the card guide and with the adaptive threshold signal having a level representative of a desired minimum threshold level for the detection of the optically encoded information and with the threshold signal adaptive to changes in the optical properties of the detector and with the means responsive to the output signal from the light detector for producing an information signal when there is a card positioned in the card guide and with the information signal representative of the optically encoded information,

means responsive to the adaptive threshold signal for storing the threshold signal, and

means responsive to the information signal and the stored adaptive threshold signal for comparing the information signal and the stored adaptive threshold signal for providing a detection of optically encoded information in accordance with such comparison.

10. The adaptive optical card reader of claim 9 wherein the means for storing the threshold signal provides for the storage on an analog basis.

11. The adaptive optical card reader of claim 9 wherein the means for storing the threshold signal provides for the storage on a digital basis.

12. The adaptive optical card reader of claim 9 wherein the information signal normally includes a first level representative of no optically encoded information and a second level representative of optically encoded information and with the adaptive threshold signal having a level between the first and second levels for the information signal.

13. The adaptive optical card reader of claim 9 wherein the means responsive to the output signal from the light detector has the signals produced in accordance with different fixed resistance values.

14. The adaptive optical card reader of claim 13 wherein the different fixed resistance values are controlled in accordance with the presence or absence of the card positioned in the card guide.

15. The adaptive card reader of claim 9 wherein the means responsive to the outlet signal from the light detector has the signals produced in accordance with resistance values provided by a variable resistor.

16. The adaptive optical card reader of claim 15 wherein the variable resistor is provided by a transistor whose absolute value is a logarithmic function of the current flowing through the transistor.

17. An adaptive threshold optical reader for detecting optically encoded information on a credit card, including

a card guide for receiving the credit card and positioning the credit card within an optical path,

a light emitting diode positioned on one side of the card guide for directing light energy along the optical path,

a photodiode positioned to the other side of the card guide for receiving light energy directed along the optical path and for producing an output current in accordance with the intensity of the received light energy,

an operational amplifier including a feedback resistance coupled to the photodiode and responsive to the output current for producing an output voltage in accordance with the output current and the value of the feedback resistance and with the feedback resistance having a first resistance value with no card in the card guide and a second resistance value with a card in the card guide,

the output voltage with the feedback resistance having the second resistance value representative of the optically encoded information on the credit card and with the output voltage with the feedback resistance having the first resistance value representative of a threshold level for the detection of the optically encoded information, and

means coupled to the operational amplifier and responsive to the output voltages with the feedback resistances having the first and second values for detecting the optically encoded information in accordance with the threshold level.

18. The adaptive threshold optical reader of claim 17 wherein the means coupled to the operational amplifier provides for the detection on an analog basis.

19. The adaptive threshold optical reader of claim 17 wherein the means coupled to the operational amplifier provides for the detection on a digital basis.

20. The adaptive threshold optical reader of claim 17 wherein the output voltage representative of the optically encoded information normally includes a first level representative of no optically encoded information and a second level representative of optically encoded information and with output voltage representative of the adaptive threshold having a level between the first and second levels for the optically encoded information.

21. The adaptive threshold optical reader of claim 17 wherein the feedback resistance is formed as a transistor in the transdiode configuration.