PIR Sensor for Solar Pathway Lighting

Project Overview

This project creates solar-powered pathway lights that automatically turn on when someone walks by. The system uses a PIR sensor to detect motion and turns on LED strips for a set duration. Solar charging keeps the battery topped up during the day.

Difficulty: Intermediate
Estimated time: 2-3 hours
Estimated cost: $30-45

How It Works

A solar panel charges a lithium battery during the day. A PIR sensor mounted on the pathway detects approaching pedestrians. When motion is detected, the system turns on LED lights for 30-60 seconds. A light sensor can be added to ensure lights only activate at night.

Materials Needed

ESP32 or ATtiny85 (1) – ATtiny85 for ultra-low power
HC-SR501 PIR sensor (1)
Solar panel (5V, 5-10W)
18650 lithium battery (1 or 2)
TP4056 charging module (with battery protection)
Boost converter (to 5V if needed)
LED strip (12V or 5V, length as needed)
MOSFET or relay (for switching LEDs)
LDR (photoresistor) (optional, for day/night detection)
Waterproof enclosure
Jumper wires and soldering equipment

Circuit Diagram

Power Section

Solar Panel (+) --- TP4056 IN+ --- 18650 Battery (+)
Solar Panel (-) --- TP4056 IN- --- 18650 Battery (-)
Battery (+) --- Boost Converter (3.7V → 5V) --- ESP32 VIN

Sensor Connections

表

Arduino Code (ATtiny85 Version – Ultra Low Power)

// Solar Pathway Lighting with ATtiny85
#include <avr/sleep.h>

const int pirPin = 0;   // PB0 (pin 5)
const int ledPin = 1;   // PB1 (pin 6)
const int ldrPin = 2;   // PB2 (pin 7)

unsigned long lastTrigger = 0;
const unsigned long lightDuration = 30000; // 30 seconds

void setup() {
  pinMode(pirPin, INPUT);
  pinMode(ledPin, OUTPUT);
  pinMode(ldrPin, INPUT);
  digitalWrite(ledPin, LOW);
  
  // Allow PIR warm-up
  delay(30000);
}

bool isDark() {
  // Read LDR (simple threshold)
  int value = analogRead(ldrPin);
  return value < 500; // Dark when below 500
}

void goToSleep() {
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);
  sleep_enable();
  sleep_cpu();
  sleep_disable();
}

void loop() {
  bool motion = digitalRead(pirPin) == HIGH;
  bool dark = isDark();
  
  if (motion && dark) {
    digitalWrite(ledPin, HIGH);
    lastTrigger = millis();
  }
  
  if (digitalRead(ledPin) == HIGH && (millis() - lastTrigger > lightDuration)) {
    digitalWrite(ledPin, LOW);
  }
  
  // Deep sleep to save battery (wake on PIR interrupt)
  if (!motion && !digitalRead(ledPin)) {
    // Enable wake on PIR change
    attachInterrupt(0, wakeUp, RISING);
    goToSleep();
    detachInterrupt(0);
  }
  
  delay(100);
}

void wakeUp() {}

ESP32 Version with Wi-Fi Monitoring

// Solar Pathway Lights with Wi-Fi Monitoring
#include <WiFi.h>

const int pirPin = 4;
const int ledPin = 5;
const int ldrPin = 34;

unsigned long lastTrigger = 0;
const unsigned long lightDuration = 30000;
float batteryVoltage = 0;

void setup() {
  Serial.begin(115200);
  pinMode(pirPin, INPUT);
  pinMode(ledPin, OUTPUT);
  pinMode(ldrPin, INPUT);
  digitalWrite(ledPin, LOW);
  
  delay(30000); // PIR warm-up
}

float readBattery() {
  // Read voltage divider (assumes 100k/100k divider)
  int raw = analogRead(36); // VP pin
  return (raw / 4095.0) * 3.3 * 2; // 2x divider factor
}

bool isDark() {
  return analogRead(ldrPin) < 500;
}

void loop() {
  bool motion = digitalRead(pirPin) == HIGH;
  bool dark = isDark();
  batteryVoltage = readBattery();
  
  if (motion && dark && batteryVoltage > 3.0) {
    digitalWrite(ledPin, HIGH);
    lastTrigger = millis();
    Serial.println("Motion detected - lights ON");
  }
  
  if (digitalRead(ledPin) == HIGH && (millis() - lastTrigger > lightDuration)) {
    digitalWrite(ledPin, LOW);
    Serial.println("Lights OFF");
  }
  
  // Report battery every 10 minutes
  static unsigned long lastReport = 0;
  if (millis() - lastReport > 600000) {
    Serial.printf("Battery: %.2fV\n", batteryVoltage);
    lastReport = millis();
  }
  
  delay(100);
}

Installation Steps

Assemble power system: Connect solar panel to TP4056, battery, and boost converter.
Test charging: Place in sun and verify battery voltage increases.
Mount PIR sensor: Place at 1m height along pathway, angled to detect pedestrians.
Install LEDs: Place LED strips along pathway edges or under handrails.
Enclose electronics: Place all components in waterproof enclosure with solar panel mounted on top.
Test: Walk along pathway at night, verify lights turn on.

Power Calculations

PIR sensor: 50µA standby
ATtiny85 sleep: 5µA
Total standby: ~55µA
Daily standby consumption: 1.32 mAh
LEDs (10W for 30 seconds, 10 events/night): 0.83 mAh
Daily total: ~2.2 mAh
18650 battery (2000 mAh) lasts: 900+ days
Solar panel ensures indefinite operation

Project Extensions

Color-changing lights: Use RGB LEDs that change color based on battery level.
Direction detection: Add second PIR to light path in direction of travel.
Remote monitoring: Add LoRa to report battery level and events.
Smart home integration: Connect to Home Assistant via MQTT.
Music sync: Add microphone for sound-reactive lighting.

Troubleshooting

Lights not turning on at night: Check LDR threshold. Test with hand covering LDR.
Lights turning on during day: Adjust LDR threshold upward.
Battery not charging: Check solar panel connections. Ensure TP4056 is working.
Short battery life: Verify deep sleep is working. Check for leaks in code.
False triggers: Adjust PIR sensitivity. Ensure not facing road traffic.

Conclusion

These solar-powered pathway lights add safety and beauty to your walkway without increasing your electric bill. With motion activation, they only illuminate when needed, saving battery power.