Application of OPT3004 in battery-powered cameras

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Application of OPT3004 in battery-powered cameras [Copy link]

 

Betty Guo

In battery-powered applications, power consumption is a very important indicator. Battery-powered cameras usually use two MCUs to implement this, one ultra-low power MCU is in long-term working state, and the main MCU is in sleep state. When the external environment changes, such as when day switches to night or when people move around, the sensor will feed back external environment information to the ultra-low power MCU, which will wake up the main MCU according to the transmitted signal to work and configure the image acquisition sensor, thereby saving energy efficiency.

In traditional long-power camera applications, low-cost photoresistors or photodiodes are often used as light-sensitive elements. The main MCU performs imaging configuration based on the image collected by the sensor, while the photodiode acts as an auxiliary light-sensitive element to jointly implement the sensor register configuration.

For battery-powered cameras, since the main MCU is in a dormant state for a long time, the perception of external light intensity is completely realized by photodiodes. Since the dynamic range of photodiodes is narrow (0Lux to 1500Lux), when the camera is in an outdoor environment, the external light intensity is very high, and light intensity saturation is prone to occur, resulting in inaccurate configuration of the image acquisition sensor and affecting the picture. On the other hand, photodiodes or photoresistors themselves also have high power consumption, which affects the use time of the system.

According to the structure of the camera, the IR LED and the optical sensor are on the same PCB board. When the infrared light is turned on, the optical sensor will receive the infrared light at the same time, so the optical sensor must have strong infrared suppression capabilities, otherwise it will lead to inaccurate parameter configuration and cause the infrared filter IR CUT to switch continuously. As shown in the following figure:

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In summary, optical sensors for battery applications must have low power consumption and high IR suppression ratio performance.

OPT3004 is a light sensor that is highly matched to the visual response of the human eye and has a high infrared blocking ability. It is the preferred alternative to photodiodes, photoresistors, etc., which have low matching degree with the human eye and poor infrared blocking ability. The measurement range is 0.01Lux to 83000Lux, with a built-in full-scale setting function and an optional response time of 100ms-800ms. OPT3004 also has excellent angular infrared blocking function, which can achieve 99% blocking of infrared incident angles above 85°.

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Even if the OPT3004 and IR LED are on the same board, due to the excellent angular incident infrared suppression capability of the OPT3004, the light intensity value collected by the OPT3004 can be approximately calculated as follows:

Natural light intensity = actual total light intensity - IR suppression intensity

Among them, the actual total light intensity refers to the total light intensity including external natural light and infrared, and the IR suppression intensity refers to the suppression ability inside the chip, which can be adjusted by 0x04 in the OPT3004 register, and the default value is 0x00. After testing, using a spectrum with a wavelength of 850nm in a dark room, when reg0x04=0x0004, the output light intensity is 0 in complete darkness, which can completely suppress the influence of infrared interference.

Here is a parameter comparison between the photodiode and OPT3004:

Through the above analysis, OPT3004 is very suitable for applications such as battery-powered cameras where the infrared light and light sensor are very close. By adjusting the infrared suppression capability by configuring register 0x04, it can perfectly replace the photodiode to solve the problems of high power consumption, narrow dynamic range and IR interference in outdoor battery-powered cameras.