Motion Detector using PIR sensor with PCB design

Step-by-Step Implementation of PIR-Based Motion Detector Using 555 Timer

Components Required

• PIR Sensor (HC-SR501)
• NE555 Timer IC
• BC547 Transistor
• Relay Module (5V)
• Resistors (1kΩ, 10kΩ, 100kΩ as required)
• Capacitor (10µF or as per timing requirement)
• Potentiometer (for adjusting delay)
• LED (for indication)
• Diode (for relay protection)
• Breadboard
• Connecting wires
• 5V Power Supply

Pin Configuration of NE555 Timer

• Pin 1 → GND
• Pin 2 → Trigger
• Pin 3 → Output
• Pin 4 → Reset
• Pin 5 → Control Voltage
• Pin 6 → Threshold
• Pin 7 → Discharge
• Pin 8 → VCC

Step 1: Understand the System Design

The PIR sensor detects motion and outputs a HIGH signal. This signal triggers the 555 timer configured in monostable mode, producing a timed output. The output drives a transistor which activates a relay to control a load.

Step 2: Connect Power Supply

• Connect Pin 8 (VCC) of 555 → +5V
• Connect Pin 1 (GND) → Ground
• Connect PIR VCC → +5V
• Connect PIR GND → Ground

Step 3: Trigger Connection (PIR to 555)

• Connect PIR OUT → Pin 2 (Trigger) of 555

Step 4: Timing Circuit Connection

• Connect resistor (R) between Pin 7 and VCC
• Connect capacitor (C) between Pin 6 and GND
• Connect Pin 6 and Pin 7 together
• (Optional) Add potentiometer in series with resistor to adjust delay

Step 5: Reset and Control Pins

• Connect Pin 4 (Reset) → VCC
• Connect Pin 5 → GND through a 0.01µF capacitor (for stability)

Step 6: Output and Transistor Connection

• Connect Pin 3 (Output) → Base of BC547 through 1kΩ resistor
• Connect Emitter of BC547 → GND
• Connect Collector → One end of relay coil

Step 7: Relay and Protection Diode

• Connect other end of relay coil → +5V
• Connect diode across relay coil (reverse biased) for protection

Step 8: Load Connection

• Connect load (bulb/fan) through relay contacts (COM and NO)

Step 9: Power On and Stabilization

Turn ON the circuit and wait 20–30 seconds for the PIR sensor to stabilize.

Step 10: Testing

• Motion detected → PIR HIGH → 555 triggered → Relay ON → Load ON
• After delay → Output LOW → Relay OFF → Load OFF

Step 11: Adjustment

• Adjust potentiometer → Change ON time
• Adjust PIR sensitivity → Improve detection range and accuracy

This setup creates a reliable motion-activated switching system suitable for basic automation and security applications.