Motion-activated basement light
In 2014 I made a motion-activated light for my basement that can be powered from a 12 volt battery. When activated, a light is switched on and remains on for about 51 seconds. The light is a 12 volt LED light tape that is attached to a piece of wood mounted on the ceiling. The device is powered by a battery which is connected to a solar panel. The circuit is based on a 555 timer for timing the light and a relay for switching the light. The circuit is shown below: Link to simulation Operation of the timer circuit The motion sensor is configured to only output a signal if the room is currently dark. The 555 timer is configured in monostable mode. When the output is off, the 555 timer shorts the discharge pin (dis) to ground. The 47μF capacitor is discharged and the threshold pin is near 0 volts as well. The 10k resistor keeps the trigger pin ( tr ) at 5 volts. When the motion sensor detects motion, it applies a positive pulse to the pin labelled "from PIR" in the schematic,