Lighting Controller with Ambient Light Sensor and Real-Time Tracker
Created: Mar 21, 2016
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Outdoor lightning is one significant mechanism that provides visibility and luminance to surroundings. Manually turning it on/off in a specific time can be a rigorous task. An intelligent outdoor lighting can be use to simplify the task by employing sensors that can substitute to human presence. The intelligent lighting controller reference design from Maxim is a lightning controller that uses MAX44009 ambient light sensor with ADC capability. The system microcontroller is the Microchip PIC18LF4520 running at an 8MHz clock frequency. The microcontroller's clock is the MAX7375 chosen for it excellent temperature coefficient and very low jitter. The system also integrated DS1340, which is a real-time clock/calendar that has the feature of providing trickle charge to the back-up supply for the system. The MAX6958 LED display driver is use to display the outputs to two 7-segment LEDs.
The reference design is powered by the main voltage AC source which is converted to 9VAC(rms) and only one voltage rail is used which is the 3V3. The ambient sensor MAX44009 can detect luminance and the on-chip photodiode spectral response is optimized to mimic the human eye’s perception of ambient light and incorporates IR and UV blocking capability. The adaptive gain block of MAX44009 automatically selects the correct lux range to optimize the whole system. The DS1340 is use to track real-time to turn off the lights in the evening where the ambient sensor functionality is not in use. The reference design has also an indicator LEDs for determining if the system is running well (OK), hour (HR) and minutes (MIN) displayed on the two 7-segment displays. The user must also consider the location of placing the ambient sensor to prevent inaccurate reading due to luminance coming from any lights near the sensor.
Furthermore, the system can run when the power is out because of the BT1 backup power source, a 0.47 mF memory-storing capacitor. When such event takes place, the RTC consumes only 1uA max current and can sustain up to 36 hours continuously. Other applications of MAX44009 can be found in smartphones, security systems, and other portable devices.