Design Article
Intelligent lighting controller measures ambient light and tracks time
Marko Kannisto and Philip Simpson, Maxim Integrated Products, Inc.
3/9/2012 10:43 AM EST
Other general design parameters
The luminaire supply is controlled by a relay with transistor T1 because of a 12V relay coil voltage. Connector J2 is used to program and debug the microcontroller.
There are also 4 indicator LEDs: power on (V_ON); system running (OK); and hour (HR) or minute (MIN) displayed on 7-segment displays with DS1 and DS2.
Positioning the ALS
Sensor placement is critical for good operation. A small hole is drilled in the luminaire chassis and is sealed with transparent tape. The ALS’ PCB is placed in the middle of the hole so the sensor “sees” and measures the ambient light level. The sensor PCB is attached to the luminaire chassis using hot glue.
Placement of the ALS should be considered carefully. If the sensor “sees” the light from the luminaire itself, it cannot measure the ambient light level correctly in the morning. This can cause the luminaire to blink on and off continuously.
In the evening, however, this ALS positioning is not an issue since the light is then switched off based on time, not based on the ambient light level.
Finally, it is almost impossible to place the ALS where it would not sense any light from the luminaire itself. For this reason, the luminaire’s switch-off lux threshold in the morning is automatically set at greater than 8 lux in the software. This compensation only ensures that the luminaire’s switch on/off happens at approximately the same ambient light level. This does not eliminate the possibility of the luminaire blinking.
System printed circuit boards (PCBs)
The controller PCB top-side and bottom-side layers are shown in Figures 6 to 8.
Figure 6 : Controller PCB part placement
Figure 7: Controller PCB top-side layer
Figure 8: Controller PCB bottom-side layer
Next: System part lists
The luminaire supply is controlled by a relay with transistor T1 because of a 12V relay coil voltage. Connector J2 is used to program and debug the microcontroller.
There are also 4 indicator LEDs: power on (V_ON); system running (OK); and hour (HR) or minute (MIN) displayed on 7-segment displays with DS1 and DS2.
Positioning the ALS
Sensor placement is critical for good operation. A small hole is drilled in the luminaire chassis and is sealed with transparent tape. The ALS’ PCB is placed in the middle of the hole so the sensor “sees” and measures the ambient light level. The sensor PCB is attached to the luminaire chassis using hot glue.
Placement of the ALS should be considered carefully. If the sensor “sees” the light from the luminaire itself, it cannot measure the ambient light level correctly in the morning. This can cause the luminaire to blink on and off continuously.
In the evening, however, this ALS positioning is not an issue since the light is then switched off based on time, not based on the ambient light level.
Finally, it is almost impossible to place the ALS where it would not sense any light from the luminaire itself. For this reason, the luminaire’s switch-off lux threshold in the morning is automatically set at greater than 8 lux in the software. This compensation only ensures that the luminaire’s switch on/off happens at approximately the same ambient light level. This does not eliminate the possibility of the luminaire blinking.
System printed circuit boards (PCBs)
The controller PCB top-side and bottom-side layers are shown in Figures 6 to 8.
Figure 6 : Controller PCB part placement
Figure 7: Controller PCB top-side layer
Figure 8: Controller PCB bottom-side layer
The MAX44009 ALS is mounted on its own PCB. Its PCB part placement, top-side and bottom-side layers are shown in Figures 9 and 10.
The ALS is connected to the controller’s PCB with connector J1.
Figure 9: ALS PCB top-side layer
Figure 10: ALS PCB bottom-side layer
The ALS is connected to the controller’s PCB with connector J1.
Next: System part lists
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docdivakar
3/14/2012 10:17 AM EDT
Seems like the value added from a utility perspective is little in comparison to many solutions that already exist there (many solar lights for gardens and walkways switch on automatically, albeit without a real time clock). If cost of adding ALS changes the lighting solution cost, it may not be worth it. I can get a timer for multiple circuits and control on-off times (the XMas tree controllers for example).
MP Divakar
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wb9ddf
3/15/2012 2:51 PM EDT
About 10 or 12 years ago I built a lighting control system with similar function for an office building I own. I used a timer and photocell from the local home improvement store. The photocell was wired in series with the timer switch contacts. The result is that the lights come on at sunset, shut off at 11:00pm, come on at 5:00am and shut off again at sunrise. The clock is mechanical so it is adjusted the old fashioned way and the photocell sensitivity is adjusted with a little black tape partially blocking the sensor. Not as sophisticated as your micro-controller but it has worked for years with little maintenance other than new light bulbs and resetting the clock after a power failure.
Fred Johnson
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docdivakar
3/16/2012 3:08 AM EDT
@wb9ddf: thank you for reinforcing my point with more detailed explanation. To be fair to the authors, there may be some value-added uses cases (perhaps industrial ones) in controlling lux-level threshold but its case hasn't been made adequately in the article.
MP Divakar
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Dr DSP
3/19/2012 12:15 PM EDT
Seems like connection with the security system might be a more important feature and where some digital control/sensing would be useful.
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anne-francoise.pele
7/16/2012 11:25 AM EDT
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