issue: April 2009 APPLIANCE Magazine
Appliance Engineer - Technology Report
Color Sensing Made Easy
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A color sensor kit helps design engineers easily identify colors beyond the human visual spectrum.
Designed to simplify the process of color identification, TT Electronics Optek Technology (Carrollton, TX, US; www.optekinc.com) introduced a color sensor evaluation kit that includes the OPB780-Kit evaluation board and the OPB780 color sensor. “With the addition of the evaluation board, the design engineer can easily utilize the color sensor with minimal design effort,” says Bob Procsal, senior applications engineer. “Just install the software onto your computer, plug in the evaluation board using a standard USB connection, and start the program. The output frequencies for each filter configuration are displayed on the monitor screen.”
With operating temperatures ranging from –30° to 85°C, the color sensor is suited for applications that will benefit from accurate color identification, such as pill sorting machinery, ink or paper color detection for office machines, or color printer calibration sensors. “For washers or dishwashers, the manufacturer can ensure that the proper soap and softener or spot remover is being used,” says Procsal. The sensor can also identify the turbidity of discharge solution by checking the color.
The OPB780 color sensor has four different frequencies relating directly to a specific color seen by the sensor. Housed in a small, lightweight package, the color sensor uses a programmable light-to-frequency convertor that combines 64 configurable silicon photodiodes and a current-to-frequency convertor on a single monolithic CMOS integrated circuit. The photodiode array consists of 16 green, clear, red, and blue filter diodes. All 16 photodiodes that have the same color filter are connected in parallel, while all 64 photodiodes are 120 × 120 μm in size and are on 144 μm centers.
The OPB780 Kit’s photodiode is designed to recognize ultraviolet, visible, and infrared wavelengths. “The maximum sensitivity wavelength is in the 850-nm range,” explained Procsal. “The device has filters to optimize the sensitivity in the blue, green, and red areas of the visible spectra. The clear filter is used if customers would like to see the sensitivity across the full spectrum between around 300 to around 1100 nm.”
According to Procsal, one design challenge encountered during the development of the color sensor was determining how to maintain a consistent amount of visible illumination on the object to be evaluated. The problem was resolved by utilizing a visible daylight white LED as the illumination source. “Repeatability of sensing color is dependent on the ability to keep all the environmental conditions as close as possible. As temperature or the light source changes, the realization of color changes. This is the same as with the human eye,” Procsal tells APPLIANCE. “The OPB780 is designed to minimize this concern with the integration of a daylight white LED into the device.”
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