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Maxim > Design Support > Technical Documents > Reference Designs > LED Lighting > APP 5320
Maxim > Design Support > Technical Documents > Reference Designs > Sensors > APP 5320
Keywords: LED, ambient light, light controller, intelligent lighting, rtc, real time clock, outdoor lighting, ALS
REFERENCE DESIGN 5320 INCLUDES: Tested Circuit Schematic BOM Software
Intelligent Lighting Controller Measures Ambient Light
and Tracks Time
By: Philip Simpson, Applications Director
Marko Kannisto
Apr 20, 2012
Abstract:
This reference
design explains how to design an intelligent lighting controller that senses and measures the
ambient light level with an ambient light sensor (ALS). Equipped with a real-time clock (RTC), the controller also knows
when to turn lighting on or off at specified times. The system presented in this document can be used to control all
luminaires that are mains-supply operated. Controller software is also provided in hex format.
Add Digital Brains to a Basic Luminaire
Outdoor lighting is usually switched on or off manually with a mechanical switch. Suppose, however, that you do not
want to illuminate an area for the whole night. In that case, it would be advantageous to control the illumination more
precisely so you can automatically switch the lighting off/on at a prescribed time.
A controller can sense ambient light, turn lights on when it gets dark, track a time interval, and automatically turn the
lights off at a specified time. In the morning, the process can be reversed. If the ambient light level is under a preset
lux threshold at a predetermined time, the system will turn on the light. It will turn the light off when the ambient gets
bright enough to surpass the same lux threshold.
It is not difficult to design an intelligent lighting controller that senses and measures the ambient light level with an
ambient light sensor (ALS). Equipped with a real-time clock (RTC), the controller also knows when to turn lighting on
or off at specified times. The system presented here can be used to control all luminaires that are mains supply
operated. The controller's lux-level threshold is fully programmable in single-lux steps. Controller software is provided
in hex format.
Integral System Components
The lighting controller in this design needs to measure the ambient light level, which is done with an ALS. There are
two different kinds of ALS products in the market today: one outputs the analog voltage proportional to the ambient
light level, and the other gives the output in digital format. This system uses the ALS with the digital output.
The controller needs to know the exact time, so a real-time clock (RTC) is used. To anticipate possible power loss, the
time information needs battery backup.
A user interface is needed for setting time and other parameters. The user interface here consists of two 7-segment
LED displays and one pushbutton. With a short button press, the system displays time and other parameters. With a
long button press, the time and parameters can be adjusted.
The system has an auto/manual switch to enable switching the light on or off manually.
System power comes from the mains supply. Electricity to the luminaire is switched on/off through a relay. The digital
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