Electrical Design
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Electrical Design of the Under-Cabinet Lights

 

The schematic below shows the block diagram of the under-cabinet lighting.

UCBlockDiagram02

The motion detector is a regular passive infrared detector. Its output goes high (3.3 V TTL-compatible) when motion is detected and remains high for about 7 seconds after motion is no longer detected. That signal is amplified and latched permanently by the ‘Latch’. It also resets (inhibits) both timers. The high output from the latch turns off the PWM (pulse-width modulator), allowing the LED controllers to produce full light output.

If motion is no longer detected, both timers are enables and start their timing. Assuming that no motion is detected, the ‘High’ timer’s output goes high after 20 minutes which, in turn, sets the PWM into a pulsed mode that produces a dimmed light output.

Should there be no motion detected for an hour, the ‘Off’ timer times out which forces the PWM controller’s output to go high, turning off the LED controllers.

If these time-out cycles are interrupted because motion is detected again, the whole process starts over.

The following pages describe the various elements that make up the whole system.

 

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