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
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
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.