Everyone knows the PIR sensor lights and how they work and sometimes they have a mind on their own. With the new cheap radar human presence detectors it is possible to solve some of the issues that a PIR sensor has. Radar detector have a real presence detection even when your not moving. It's radar soo it's immune of false positive detections because of changing lights, a bee, moving hot air ....

The HLK-LD2410 is such a sensor. You can config the behavior via a standard FT232 and your PC. Once configured you have an OUT pin that goes high when a person is in it's range. In order to have it react like a sensor light, darkness has to be detected....

This is done via a LDR resistor and an TL431 (U1) is used as comparator. RP1 allows to configure darkness threshold. Once darkness has detected the HLK-LD2410 is powered on via P-channel mosfet Q1 and an MP1584 step down power module. If a person is detected the HLK-LD2410 generates a 3.3V on it's OUT pin and this switches n-channel powermosfet Q2 on and let there be light..;-)

When your light is feedback into the LDR the light would switch off and this would result in an oscillating loop. To avoid this disco lighting there is a second TL431 U2 who forces the light on when the HLK-LD2410 it's output is high.

It's a simple analog circuit with an advanced cheap sensor. Hope it will help you with the convienience of a relieable lighting.

Any sugestions on how to improve the circuit are welcome.