Browse Prior Art Database

Adjustment of LED Current in Optical Document Sensor

IP.com Disclosure Number: IPCOM000040618D
Original Publication Date: 1987-Dec-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Kobayashi, Y: AUTHOR

Abstract

In an optical document sensing unit such as for the bill recognition unit in the banking terminal comprising a light-emitting diode (LED) and photo sensor, the lowering of efficiency due to dust built up thereon and the dispersion of amplification factors for the sensor are compensated by adjusting the LED current to produce a predetermined intensity of radiation of the LED, enabling the sensor to positively sense the document passing through the sensing unit. The main processor 1 sets a value in the 6-bit data latch 2 defining an optimum LED current and, then, the data latch 2 produces C code indicative of the value. On the other hand, the crystal oscillator 3 advances the 8-bit free running counter 4 to generate the 8-bit A code which periodically indicates the values of 0 to 255.

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Adjustment of LED Current in Optical Document Sensor

In an optical document sensing unit such as for the bill recognition unit in the banking terminal comprising a light-emitting diode (LED) and photo sensor, the lowering of efficiency due to dust built up thereon and the dispersion of amplification factors for the sensor are compensated by adjusting the LED current to produce a predetermined intensity of radiation of the LED, enabling the sensor to positively sense the document passing through the sensing unit. The main processor 1 sets a value in the 6-bit data latch 2 defining an optimum LED current and, then, the data latch 2 produces C code indicative of the value. On the other hand, the crystal oscillator 3 advances the 8-bit free running counter 4 to generate the 8-bit A code which periodically indicates the values of 0 to 255. The A code is compressed into the 6-bit B code by the data compressor 5 to periodically indicate the values of 0 to 63 corresponding to the A code indicative of 0 to 255 in the same period. This data compression is made by the non-linear conversion, as follows: A code (8-bit) B code (6-bit)

1 to 15 1 to 15

16 to 31 16 to 23

32 to 127 24 to 47

128 to 255 48 to 63 The data compression can be approximately expressed by correlating the A code to the square of B code, so the compression keeps the substantial resolution of adjusting the lower LED current. Then, the B code is successively compared with the C code in the data comparator 6 to generate the PWM wave which is at the high level during the B co...