PIR Motion Sensing Security Light Circuit

This PIR Motion Sensing Security Light Circuit is a very nice project for person who love electronics.

The light in this circuit have special sensor for security.

Normal switch are used to turn light ON and OFF by hand.

But this light is different it is having motion sensor inside.

Sensor can see the movement like someone is walking.

If thee is no movement then light stay ON but look little dim.

It work like a nightlight but for place not used much like hallway or outside.

When sensor sees someone moving then light become more bright for few minutes.

And then the light become dull again.

Some people may feel strange because light goes OFF by itself.

Still this idea is smart to stop someone coming at night, even it does not save much electricity.

Circuit Working:

Parts List:

This circuit uses one white LED and 3.3V 5W power.

After making the circuit better to put it inside a box.

We can fix this device on wall or ceiling and inside our house or outside.

To give power we need 12V DC adapter which should be at least 1 Amp output.

If we want to use more LEDs like two or three then we can connect in series but we just need to change resistor R5 value.

Be sure power supply is strong enough for more LEDs.

When in standby PIR sensor give 0V so transistor T1 stay OFF.

When C1 charge through R2 and D1 then transistor T2 turn ON and LED1 light up.

When PIR sees movement then T1 turn OFF T2 and so LED slowly goes OFF.

To change how long light stay ON we can just adjust C1 and R4 values.

PIR sensor gives high signal to around 3.3V for short time, then it goes back to low to 0V.

Using sensor and its small knob like potentiometer we can change signal time.

At the end resistor R5 control how much current goes to LED1.

In the circuit while testing R5 was 6 ohm 3W resistor.

Formula:

PIR (Passive Infrared) sensor have two parts and these two parts must stay in balance for right motion detection.

Below is small summary with formula and meaning:

Formula:

|Va – Vb| / (Va + Vb) × 100%

Explanation:

• |Va – Vb| mean how much different voltage is between sensor part A and part B.
• (Va + Vb) is the total voltage of both parts.
• Divide and multiply by 100% it give percentage for difference.

Why Balance is Important:

PIR sensor uses two sensing parts, one part compare with other to see if something is moving.

And the other part is more sensitive than first one, its sensor may turn ON when there is no real motion.

Balancing both parts help to reduce wrong alarms.

Testing and Setting:

SSOV Single Signal Output Voltage:

Test each part A and B one by one with infrared light and measure voltage in millivolt (mV).

Look at the highest and lowest voltage, this is peak to peak.

Use Formula:

Put the Va and Vb from test into the formula:

|Va – Vb| / (Va + Vb) × 100%

This shows how much difference is in percent and use | | for absolute value to make result always positive.

Understanding the Result:

Each PIR sensor type have different good balance range.

But smaller percentage is near 0% which is usually better.

If result is not in good range then sensor may need fixing at factory which is not easy to fix by self.

Final Note:

Balancing ensures both sensor parts work the same.

It help to find right balance using number so company can adjust sensor for best work.

How to Build:

To build a PIR Motion Sensing Security Light Circuit the steps mentioned below needs to the followed:

Circuit Schematic:

• First look at circuit diagram carefully and this will help to know where each part goes and how to connect them.

Put Parts on Breadboard:

• Before soldering test all parts on breadboard.
• Use jumper wires to connect parts same like circuit diagram.

Solder the Parts:

• After testing is okay move parts to PCB or perf board.
• Solder them well so no short circuit happen and connection is good.

Connect PIR Sensor:

• Now connect PIR sensor same as in diagram.
• PIR usually have 3 pins output, ground and power.
• Check sensor datasheet to be sure pin connections are correct.

Finish the Circuit:

• When all parts are connected put the circuit inside a box to protect from weather.
• Be sure PIR sensor can see clearly to detect motion.

Connect LED:

• Connect white LED1 with correct polarity with + and -.
• If using more LEDs then connect them in series.

Power Supply:

• Before connecting 12V DC power check if the power source can give enough current.

Make Changes if Needed:

• If want light to turn OFF slower or faster then change value of C1 and R4.
• Use the small knob like potentiometer on PIR sensor to change motion sensitivity.

Testing:

• Turn circuit ON.
• Check if LED lights when it sees motion.
• After some time LED should turn OFF slowly.

Mounting the Light:

• Fix the PIR sensor light in good place where it can detect motion easily.
• Put it where needed like hallway or outside.

Conclusion:

This PIR Motion Sensing Security Light Circuit turns ON when it sees the movement.

This circuit is cheap and saves power and is good for outdoor lighting.

References:

Motion detector