Colour sensor for miniature applications

Paul Boughton

Providing design engineers a reflective sensor with the capability to reliably sort or match surfaces by colour, TT electronics OPTEK Technology has developed its OPB780 reflective colour sensing assembly.

Applications where the colour sensor is being implemented include pill sorting machinery in pharmaceutical applications, ink and/or paper colour detection for office machines, colour printer calibration sensors, as well as colour-match sensing in paint, textile and cosmetic manufacturing.
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The assembly's white LED illuminates the surface of the object or liquid being sensed, with the reflected light then received by an 8 X 8 photodiode array.

The array consists of four selectable groups of red-, green-, blue- and clear-filtered photodiodes, with each group of 16 photodiodes integrating the reflected filtered light to minimise any non-uniformity.

A light-to-frequency converter in the CMOS monolithic sensor enables the assembly to communicate directly with a micro-controller, producing a square wave output with a frequency directly proportional to light intensity.

Operating from a 5V power supply, the OPB780 Series colour sensor has a typical nonlinearity error of 0.2 per cent at 50kHZ. The LED in the colour sensor assembly has a typical luminous intensity of 1100mcd and a typical forward voltage of 3.6V.

Maximum forward current is 30mA, with a pulse forward current of 100mA. The maximum reverse voltage is 5V with a power dissipation of 120mW.

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