Abstract: The TCS230 is a programmable color light-to-frequency sensor manufactured by TAOS Corporation, USA. This sensor features high resolution, programmable color selection and output calibration, and single-power supply; its output is digital and can be directly connected to a microprocessor. This paper mainly introduces the principle and application of the TCS230, as well as the knowledge of colored light and white balance, and uses an example to illustrate the color recognition process of the TCS230. Keywords: TCS230, color sensor, color recognition, white balance adjustment Introduction With the development of modern industrial production towards high speed and automation, color recognition, which has long been dominated by the human eye, will increasingly be replaced by corresponding color sensors. For example, libraries use color differentiation to classify documents, which can greatly improve shelving management and statistical work; in the packaging industry, product packaging uses different colors or decorations to indicate its different properties or uses. Current color sensors typically consist of separate photodiodes covered with modified red, green, and blue filters. The output signal is then processed to identify the color. Some combine both methods, but the output is an analog signal requiring an A/D circuit for sampling and further processing before identification, increasing circuit complexity and introducing significant recognition errors, thus affecting the accuracy. TAOS (Texas Advanced Optoelectronic Solutions)'s latest color sensor, the TCS230, not only enables color recognition and detection but also boasts many superior new features compared to previous color sensors. 1. TCS230 Chip Structure and Features: The TCS230 is a programmable color light-to-frequency converter from TAOS. It integrates a configurable silicon photodiode and a current-to-frequency converter onto a single CMOS circuit, while also integrating red, green, and blue (RGB) filters on a single chip. It is the industry's first RGB color sensor with a digitally compatible interface. The TCS230's output signal is digital, capable of driving standard TTL or CMOS logic inputs, thus allowing direct connection to microprocessors or other logic circuits. Because the output is a digital value and it can achieve a conversion accuracy of more than 10 bits per color channel, an A/D conversion circuit is no longer needed, simplifying the circuit. Figure 1 shows the pinout and functional block diagram of the TCS230. In Figure 1, the TCS230 uses an 8-pin SOIC surface-mount package, integrating 64 photodiodes on a single chip. These photodiodes are divided into four types: 16 photodiodes have red filters; 16 have green filters; 16 have blue filters; and the remaining 16 have no filters, allowing all light information to pass through. These photodiodes are arranged in a staggered pattern within the chip, minimizing the non-uniformity of incident light radiation and thus increasing the accuracy of color recognition. Furthermore, the 16 photodiodes of the same color are connected in parallel, evenly distributed in the diode array, eliminating positional errors in color. During operation, the required filter is dynamically selected via two programmable pins. The sensor's typical output frequency range is from 2 Hz to 500 kHz. Users can also select an output scaling factor of 100%, 20%, or 2%, or a power-off mode, via two programmable pins. The output scaling factor allows the sensor's output to adapt to different measurement ranges, improving its adaptability. For example, when using a low-speed frequency counter, a small calibration value can be selected to match the TCS230's output frequency to the counter. As shown in Figure 1, when incident light is projected onto the TCS230, different filters can be selected through different combinations of photodiode control pins S2 and S3; after passing through a current-to-frequency converter, square waves of different frequencies (duty cycle of 50%) are output, with different colors and light intensities corresponding to different frequency square waves; different output scaling factors can also be selected through output calibration control pins S0 and S1 to adjust the output frequency range to meet different needs. Figure 1: TCS230 Pin and Functional Block Diagram. The functions of each pin of the TCS230 chip and some of its combination options are briefly introduced below. S0 and S1 are used to select the output scaling factor or power-off mode; S2 and S3 are used to select the filter type; OE is the frequency output enable pin, which can control the output state. When multiple chip pins share the microprocessor's input pin, it can also be used as a chip select signal; OUT is the frequency output pin, GND is the chip's ground pin, and VCC provides the chip's operating voltage. Table 1 shows the available combinations of S0, S1, S2, and S3. Table 1: Combination Options of S0, S1, S2, and S3 2. The Principle of TCS230 Color Recognition As can be seen from the above introduction, this programmable color light to frequency converter is suitable for colorimeter measurement applications, such as color printing, medical diagnostics, computer color monitor calibration, and process control and color matching in paints, textiles, cosmetics, and printing materials. The following uses the application of TCS230 in liquid color recognition as an example to introduce its specific use. First, let's understand some knowledge about light and color. (1) The principle of primary color sensing: The color of an object that we usually see is actually the reaction of the human eye to the colored components of the white light (sunlight) that the object's surface absorbs and reflects. White is composed of a mixture of visible light of various frequencies, that is, white light contains various colors of light (such as red (R), yellow (Y), green (G), cyan (V), blue (B), and violet (P). According to the theory of primary colors by the German physicist Helinholtz, various colors are composed of different proportions of the three primary colors (red, green, and blue). (2) The principle of TCS230 color recognition: According to the principle of primary color sensing, if we know the values ​​of the three primary colors that make up various colors, we can know the color of the object being tested. For TCS230, when a color filter is selected, it only allows a certain primary color to pass through and blocks the passage of other primary colors. For example, when a red filter is selected, only red light can pass through the incident light, while blue and green light are blocked, thus obtaining the intensity of red light. Similarly, by selecting other filters, the intensity of blue and green light can be obtained. Through these three values, the color of the light projected onto the TCS230 sensor can be analyzed. (3) White Balance and Color Recognition Principle White balance tells the system what white is. Theoretically, white is made up of equal amounts of red, green and blue; however, in reality, the three primary colors in white are not completely equal, and for the TCS230 light sensor, its sensitivity to these three primary colors is different, resulting in the TCS230's RGB output being unequal. Therefore, white balance adjustment must be performed before testing to ensure that the TCS230 recognizes the three primary colors in the detected "white" as equal. White balance adjustment is to prepare for subsequent color recognition. In this device, the specific steps and methods for white balance adjustment are as follows: Place an empty test tube above the sensor, and place a white light source above the test tube so that the incident light can pass through the test tube and illuminate the TCS230; according to the method described above, sequentially select the red, green, and blue filters, and measure the values ​​of red, green, and blue respectively, and then calculate the three required adjustment parameters. When using the TCS230 to identify colors, these three parameters are used to adjust the R, G, and B values ​​of the measured color. There are two methods to calculate the adjustment parameters: ① Sequentially select the three color filters, and then count the output pulses of the TCS230 sequentially. Stop counting when the count reaches 255, and calculate the time used for each channel. These times correspond to the time base used by each filter of the TCS230 during actual testing, and the number of pulses measured within this time period is the corresponding R, G, and B values. ② Set the timer to a fixed time (e.g., 10 ms), then select the filters for the three colors, calculate the number of output pulses of the TCS230 during this time, and calculate a scaling factor. This scaling factor can be used to convert these pulse counts to 255. In actual testing, use the same time to count, multiply the measured pulse count by the calculated scaling factor, and then you can obtain the corresponding R, G, and B values. 3. Application of TCS230 – Color Recognition Circuit Based on the above analysis, a medical liquid color recognition device is designed using the 89C51 and TCS230. This device features a simple structure, high recognition accuracy and efficiency, and can communicate with a host computer to transmit the recognition results to the host computer in real time. Since this describes the use of the TCS230, only the TCS230 recognition circuit is shown below, as shown in Figure 2. Figure 2 shows the use of several pins of the P1 port of the 89C51 to control the various control pins of the TCS230, while the output pins of the TCS230 are connected to the input terminal (P35) of the 89C51's Timer/Counter 1. The 89C51 Timer/Counter is set to the corresponding operating mode, initialized to a fixed value, and then the output scaling factor of the TCS230 is selected, and the output pins are enabled. In actual use, by reading the value of the 89C51 counter, the three output frequencies of the TCS230 can be calculated, thereby determining the R, G, and B values ​​and the color. The corresponding software flow is shown in Figure 3. In the program flow of the TCS230 color recognition interface circuit in Figure 2: System initialization is responsible for setting the operating mode of the 89C51 Timer/Counter, selecting the output scaling factor of the TCS230, enabling the output pins, and setting the communication parameters. After initialization, it checks whether white balance adjustment is needed. If so, the white balance subroutine is adjusted; otherwise, it proceeds to the next step to check whether color recognition is needed. If color recognition is not required, return; if color recognition is required, call the color recognition subroutine until color recognition is complete. Figure 3 Software Flow 4. Issues to Note in Application ① Avoid interference from external light during color recognition, otherwise it will affect the color recognition results. It is best to place the sensor, light source, etc. in a sealed, non-reflective box for testing. ② There are no special requirements for the light source, but the light emitted by the light source should be as concentrated as possible, otherwise it will cause mutual interference between sensors. ③ When using TCS230 for the first time, or when the TCS230 recognition module is restarted, or when the light source is changed, white balance adjustment is required. Conclusion This article starts from the structural characteristics of TCS230, introduces the knowledge of color light theory and color recognition, as well as the principle of white balance and the method of adjustment. Combined with a specific application, the corresponding hardware design circuit and software flowchart are given. This sensor and the method introduced in this article are also very helpful for other color recognition applications.