Simple PIR Motion Sensing Security Light Circuit

This is a fun electronics project for a hobbyist.

It is a security light that uses a special sensor.

Regular light switches turn the light on and off manually.

This light is different it has a motion sensor.

The sensor detects movement like someone walking by.

When there is no movement the light stays on dimly.

This is like a nightlight but only in places you do not use all the time, like hallways or outside.

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

Then it goes back to being dim.

This might confuse someone who does not expect the light to turn off.

This project might not save a lot of energy, but it is a clever way to deter someone from coming onto your property at night.

Circuit Working:

Parts List:

Examining the simple and basic circuit diagram, the prototype employs a single white LED 3.3V 5W as the light source.

Once constructed the entire circuit should be enclosed suitably.

This versatile unit can be installed indoors or outdoors on walls or ceilings within the detection area.

Powering the PIR security light requires an external 12V DC power source with a minimum output current capacity of 1 Amp.

Should you wish to modify the light source you can connect two or three white LEDs in series configuration without altering the circuit significantly except for adjusting the value of resistor R5.

It is crucial to ensure that the external power sources output current meets the increased demand.

In standby mode the PIR sensor module outputs 0V, keeping the transistor T1 off.

Capacitor C1 charges through R2 and D1 activating transistor T2 and turning on the light source LED1.

Upon motion detection, the PIR sensor module triggers T1 to cut off T2 initiating a gradual turn off of the light source.

The turn off delay can be adjusted by altering the values of C1 and R4.

Notably, the PIR sensor module outputs a high level signal near 3.3V for a finite duration after motion detection returning to a low level signal 0V thereafter.

The duration of this signal can be modified using the on board potentiometer of the PIR sensor module.

Finally, resistor R5 regulates the operating current of the light source LED1.

In the prototype a 6 ohm power resistor 6Ω 3W is used for R5 during testing.

Formula:

Accurate motion detection in PIR (Passive Infrared) sensors with dual components depends on balancing the sensing element output.

Below is a summary of the justification and the formula:

|Va – Vb| / (Va + Vb) x 100%

where,

• |Va – Vb|: This component shows the precise difference in voltage output (sensitivity) between the PIR sensors elements A (Va) and B (Vb).
• Regardless matter which element has a larger voltage output, the absolute value guarantees a positive difference.
• (Va + Vb): The total of the two components’ sensitivities is shown in this section.
• It serves as the systems overall reference value.
• x 100%: In this section, the result is converted to a percentage from a decimal number between 0 and 1, which represents the relative difference.

The Importance of Balancing

PIR sensors that have two sensing elements depend on one elements ability to measure changes in infrared radiation in comparison to the other.

If the elements differ in their sensitivity (the amount of voltage they produce for a given amount of radiation), imbalances may cause the sensor to activate even in the absence of motion.

Because of their intrinsic disparities, balancing minimizes false alarms by ensuring that both constituents have similar sensitivity.

Configuration and Testing:

Single Signal Output Voltage (SSOV): When subjected to a regulated infrared radiation source, each elements voltage output (sides A and B) is measured separately.

The highest positive and negative swings of the voltage signal are represented by this voltage, which is commonly measured in millivolts (mV) peak to peak.

Balance Formula: The percentage difference between the two components SSOVs (Va and Vb) is then computed using the formula: |Va – Vb| / (Va + Vb) x 100%.

• The absolute value guarantees a positive change, as previously said.
• The value between 0 and 1 is normalized by dividing by the total.
• The difference is expressed as a percentage when multiplied by 100%.

Interpretation and Adjustment: Although the optimal balancing value varies depending on the particular sensor type, a percentage difference as near to 0% is usually preferred.

An acceptable tolerance range for the balance value may be specified by the manufacturer.

The sensor may need to have changes made during the manufacturing process if the computed percentage difference is not within an acceptable range (this is not something you can usually do yourself).

In PIR sensors, overall, balancing the sensing element outputs guarantees that both elements are proportionally responsive to changes in infrared radiation.

The methodology helps manufacturers calibrate the sensors for best performance and offers a quantitative method of evaluating this balance.

How to Build:

Building the PIR Security Light involves assembling the electronic components according to the provided circuit diagram and then enclosing the circuit in a suitable housing.

Circuit Diagram:

• Familiarize yourself with the circuit diagram to understand the placement and connections of each component.

Connect the Components on a Breadboard:

• Before soldering the components, you can use a breadboard to test the circuit.
• Connect the components as per the circuit diagram using jumper wires.

Solder the Components:

• Once the circuit is tested on the breadboard transfer it to a perforated board or PCB.
• Solder the components onto the board ensuring proper connections and avoiding short circuits.

Connect the PIR Sensor:

• Connect the PIR sensor module to the circuit as per the diagram.
• The sensor typically has power, ground, and output pins.
• Follow the datasheet or module documentation for proper connections.

Enclose the Circuit:

• Place the completed circuit inside a suitable enclosure to protect it from environmental elements.
• Ensure that the PIR sensor has a clear line of sight for motion detection.

Connect the LED:

• Connect the white LED LED1 to the circuit ensuring the correct polarity.
• If you want to use multiple LEDs connect them in series configuration.

Power Supply:

• Connect the external 12V DC power source to the circuit, ensuring that the current capacity meets the requirements.

Adjustments:

• Fine tune the circuit by adjusting the values of C1 and R4 to achieve the desired turn off delay.
• Follow the PIR sensor module documentation to adjust its sensitivity and motion detection settings using the on board potentiometer.

Testing:

• Power on the circuit and test its functionality.
• Verify that the LED turns on in standby mode and gradually turns off after motion detection.

Mounting:

• Mount the PIR Security Light in the desired location considering the detection area and ensuring it is positioned for effective motion sensing.

Conclusion:

To conclude, overall motion sensing security lights provide an effective and energy efficient solution for enhancing security and illuminating outdoor spaces by responding to detected motion in their proximity.

References:

Motion detector