Motion Sensor Light


Turns on a White LED for 3 minutes and turns off when a human move in front of it. Uses Passive Infra Red (PIR) motion sensor.

Components required
470 Ohms resistor – 1
10 K resistor – 1
47 K resistor – 1
1N 4148 Diode – 1
IC CA 3140 ( or LM 741 ) – 1
5 mm White LED – 1
PIR Motion Sensor – 1
9 V or 12 Volt battery or Adaptor


Working
IC CA 3140 is wired as a Voltage comparator. Its Inverting input is held at a fixed voltage of 2.13 volt by the 47 K and 10 K potential divider. Non Inverting input of IC gets a higher voltage of 3.3 volts from activated PIR sensor (PIR Motion sensor gives 3.3 V output when activated).

When the circuit is stand by, at 12 V , voltage at the Inverting input is 2.13 volt and voltage at the Non inverting input is 0 or few milli volts. Since the voltage at the Inverting input is higher than Non inverting input of the comparator, its output remains low. So LED remains off.

When a human passes in front of the PIR sensor, its output turns high and apply 3.3 volts in the Non inverting input of the comparator. Now the voltage at the Non inverting input is higher than the Inverting input and the output of comparator swings high and LED lights.

Sensitivity ( Detection range ) of PIR sensor can be adjusted from 30 cm to 10 Meters and the Time delay from 30 seconds to 3 minutes using the presets.