Simple PIR Motion Sensing Security Light Circuit

This project is just fascinating for an electronics lover.

The security light in this circuit uses a special sensor.

Standard light switches are used to manually turn the light ON and OFF.

Unlike other lights this one has a motion sensor built in.

The sensor detects movement like a person walking by.

When there is no motion the light stays ON which seems although like dimly.

This works similarly to a nightlight but only in places that people do not use often such hallways or outdoor areas.

If the sensor detects movement the light gets brighter for a few minutes.

After that it gets dull once again.

This could be a little disturbing for someone who does not know the light is going out.

This idea is a clever way to keep someone off the property at night even if it might not save a lot of electricity.

Circuit Working:

Parts List:

According to the simple circuit design above the prototype uses a single white LED with a 3.3V 5W power source.

After construction is complete the circuit should be properly enclosed.

This adaptable device should be mounted on the walls or ceilings of the detecting area both indoors and outdoors.

An external 12V DC power source with a minimum output current capacity of 1 Amp is needed to power the PIR security light.

If one wishes to change the light source it may connect two or three white LEDs in series without making any major changes to the circuit other than changing the resistor R5 value.

It is essential to be sure that the output current of external power sources can keep up with increasing demands.

The transistor T1 is kept off in standby mode by the PIR sensor modules 0V output.

Transistor T2 is activated and the light source of LED1 is turned ON when capacitor C1 charges through R2 and D1.

The light source slowly turns OFF when the PIR sensor module detects motion causing T1 to shut OFF T2.

The values of C1 and R4 is changed to modify the switch off delay.

PIR sensor module releases a high level signal close to 3.3V for a limited amount of time before switching back to a low level signal at 0V.

With the use of the PIR sensor modules and onboard potentiometer the signals duration can be changed.

Finally resistor R5 controls the light source of LED1 functioning current.

During testing R5 in the prototype is powered by a 6 ohm 6Ω 3W resistor.

Formula:

PIR (Passive Infrared) sensors with two components must balance the output of the sensing element so as to detect motion correctly.

A summary of the formula and its explanation is mentioned below:

|Va – Vb| / (Va + Vb) x 100%

where,

• The Va – Vb| component shows the accurate difference in voltage output (sensitivity) between PIR sensor components A (Va) and B (Vb).
• The total of the two components sensitivities (Va + Vb) is shown in this section.
• The result switches from a numeric number between 0 and 1 which indicates the relative difference to a percentage x 100% in this section.

The Value of Balance:

Two sensing PIR sensors rely on one elements capacity to detect changes in infrared radiation compared to the other.

The imbalances may result in the sensor activating even when there is no motion if the elements have different sensitivity (the amount of voltage they produce for a given amount of radiation).

By ensuring that both parts have equal sensitivity balancing lowers false alarms due to the way they are designed.

Configuration and Testing:

SSOV or single signal output voltage:

Each elements voltage output (sides A and B) is monitored separately after being exposed to a controlled infrared radiation source.

This voltage which is often expressed in millivolts (mV) peak to peak represents the voltage signals greatest positive and negative swings.

The Balance Formula:

The formula |Va – Vb| / (Va + Vb) x 100% is then used to get the percentage difference between the two components SSOVs (Va and Vb).

As said before the absolute value ensures a positive change.

By dividing by the total the value between 0 and 1 is leveled.

When multiplied by 100% the difference is represented as a percentage.

Interpretation and Modification:

While each type of sensor has a different optimal balancing value a percentage difference as close to 0% is often better.

The manufacturer can provide an acceptable tolerance range for the balancing value.

If the calculated percentage difference is not within an acceptable range the sensor may need to be modified during the manufacturing process (this is not something one could normally do it alone).

Finally balancing the outputs of the sensing components in PIR sensors ensures that both elements respond equally to changes in infrared radiation.

This technique provides a quantitative way to assess the balance and helps manufacturers in tuning the sensors for the best results.

How to Build:

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

Circuit Schematic:

• Read the circuit diagram thoroughly so that one understands the locations and connections of every component.

Connect the Parts to the Breadboard:

• Test the circuit on a breadboard before soldering the parts.
• Use jumper wires to connect the parts according to the circuit schematic.

Solder the parts together:

• After testing the circuit on a breadboard move it to a PCB or perforated board.
• In order to prevent short circuits and ensure correct connections solder the components onto the board.

Connect the PIR sensor:

• As shown in the circuit diagram connect the PIR sensor module to the circuit.
• Usually the sensor contains output, ground and power connections.
• For correct connections refer to the datasheet or component datasheet.

Complete the Circuit:

• To protect it from the weather the completed circuit has to be put within the correct enclosure.
• A clear line of sight is necessary for the PIR sensor to detect motion.

Connect the LED:

• Check weather white LED1 have the correct polarity when connected to the circuit.
• If one is having more than one LEDs than it can be used by connecting them in series.

Source of Power:

• Be sure the circuit has enough current capacity before connecting the external 12V DC power source.

Modifications:

• To get the required turn OFF delay fine tune the circuit by changing the values of C1 and R4.
• Use the on board potentiometer to modify the PIR sensor modules sensitivity and motion detection settings to meet with the specifications.

Testing:

• Turn the circuit ON and check that its working.
• Check that when motion is detected the LED lights up while in standby mode and then slowly shuts off.

Mounting:

• Check the PIR security light has been placed for efficient motion detection and mount it in the chosen spot keeping note of the detection area.

Conclusion:

The motion sensing security lights circuit responds to motion detected in the the area by giving a cost effective and energy efficient way for improving outdoor lighting and security.

References:

Motion detector