Application of light sensor in intelligent lighting control system

With the improvement of people's living standards, people have higher and higher requirements for lighting control, such as creating a comfortable lighting environment, saving energy, and improving the life of the light source. In order to improve the comfort of the working environment, the lighting control system adopts a light sensor to automatically control the lighting device according to the illumination of the current environment, so that the illumination is controlled within a comfortable range.

In conventional lighting control systems, a common optical sensor combined with an A/D converter (ADC) scheme is often used. On the one hand, since the optical signal detected by the photosensor contains both the visible component and the infrared component, the influence of filtering the infrared light on the detection result of the photosensor should be considered in the design, and the design is complicated due to the use of the separated device. On the other hand, the detection range of the contrast is relatively limited, which is not conducive to the realization of multi-channel illumination detection to implement sub-regional control of multiple lighting devices in the same place. A multi-channel illumination detection scheme based on ISL29004 is proposed to simplify the system design, and the single-chip microcomputer P87LPC768 is used as the control core of the intelligent lighting control equipment to realize sub-regional control of multiple lighting equipments, which is more comfortable in energy saving. Lighting environment.

1 I2C device ISL29004

1.1 I2C Bus Overview

The I2C bus is an inter-chip serial transmission bus introduced by PhiIips. It is transmitted in two lines. All the nodes on the bus, such as the main device (single chip, microprocessor), peripheral devices, interface modules, etc., are connected to the SDA and SCL of the same name. In the above, a perfect half-duplex synchronous data transmission is realized, which can conveniently constitute a multi-machine system and a peripheral device expansion system. The I2C bus adopts the hardware setting method of the device address, and the chip-selection line addressing method of the device is completely avoided by software addressing, thereby making the hardware system have a simple and flexible expansion method.

The I2C bus transmission data must follow the specified data transmission format. The data transmission is controlled by the main controller. The main controller initiates the data transmission, the transmission start signal, the addressing information, and the stop signal when the transmission ends. The controller performs the necessary answer.

1.2 Light Sensor ISL29004

The ISL29004 is a next-generation optical-to-digital sensor that integrates a current amplifier, a 50Hz/60Hz rejection filter for eliminating artificial light flicker, and a 16-bit adc that converts illumination into an easy-to-use 16-bit, I2C standard digital output signal. The user provides a single chip solution. The ISL29004 has two photodiodes inside. Diode 1 detects the total illuminance of visible and infrared light in the environment. Diode 2 only detects the infrared illuminance in the environment. The spectral response of the two diodes is independent of each other. The user can programmatically control the working mode of the adc, which can output only the detection result of the photodiode 1 or 2, and in the mode 2, the result of filtering out the infrared light calculated by the internal subtraction function can also be output. The ISL29004 has eight 8-bit registers, one command register, one control register, two interrupt threshold registers, and four read-only data registers. The command register can set the working mode and resolution of the ADC; the control register can adjust the gain to select the illumination detection range; the read-only data registers LSB_Sensor and MSB_Sensor can read the nearest digital output of the ADC; the read-only data registers LSB_timer and MSB_timer can be read. The number of cycles in which the ADC was last integrated. The addresses of the eight registers are 00H to 07H in order.

ISL29004 has two I2C interface address selection pins A0, A1, which can install four ISL29004 on one I2C bus line and can coexist with other I2C peripheral nodes.

2 hardware structure and working principle

2.1 Overall structure

The block diagram of the system is shown in Figure 1. The MCU P87LPC768 is used as the main controller of the I2C bus, ISL29004 is used as the controller, and the device addresses of the four ISL29004 are: 44H to 47H, which are set by the address pins A1 and A0 of the ISL29004. In the system, the quasi-bidirectional I2C bus buffer P82896 is used to drive and expand the I2C bus, realize the long-distance transmission of the I2C bus, and expand the illumination collection distance; the I2C bus of the P87LPC768 is extended by the P82896 buffer and then through the twisted pair and the far The P82896 and ISL29004 are connected. Corresponding to the four sets of illumination acquisition circuits, the dimming control circuit also has four groups connected to the four PWM pins of the P87LPC768.


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