Energy Harvesting PIR Sensor with Solar Power

Project Overview

This project creates a self-powered PIR motion sensor that runs entirely on solar energy. It is ideal for remote locations where running power cables or changing batteries is impractical. The system stores energy in a supercapacitor or rechargeable battery, providing operation through the night.

Difficulty: Advanced
Estimated time: 4-6 hours
Estimated cost: $40-60

How It Works

A small solar panel charges a supercapacitor or lithium battery during the day. An ultra-low power PIR sensor (Excelitas PYD 2597 or Panasonic EKMB) draws only 2-6 µA, allowing continuous operation. When motion is detected, the system wakes a microcontroller to process the event and optionally transmit via low-power radio (LoRa, Zigbee, or Bluetooth).

Materials Needed

• Ultra-low power PIR sensor (Excelitas PYD 2597 or Panasonic EKMB 1µA variant)
• ESP32-C3 or nRF52840 (low-power microcontroller)
• Solar panel (5V, 100-200mA, 80x80mm or larger)
• TP4056 charging module (if using Li-ion battery)
• Lithium battery (18650 or LiPo, 1000-2000mAh) OR
• Supercapacitor (2x 10F 2.7V in series for 5F 5.4V)
• Low-dropout regulator (MCP1700, 2µA quiescent)
• Schottky diode (1N5819) for solar panel isolation
• LoRa module (RAK811 or Heltec) or BLE module (optional)
• Waterproof enclosure (IP65 rated)

Circuit Diagram

Power Management Section

Solar Panel (+) --- Schottky Diode ---+--- TP4056 IN (if using battery)
                                       |
                                       +--- Supercapacitor (+) (if using cap)
                                       |
                                       +--- LDO (MCP1700) IN
                                       |
Supercapacitor/Battery (-) ------------+--- LDO GND
                                       |
LDO OUT (3.3V) ------------------------+--- PIR VCC
                                       +--- MCU VCC

Sensor Connection

VCC

3.3V

GND

GND

OUT

GPIO (with 10k pull-up to 3.3V)

WUP

GPIO (interrupt pin)

表

Arduino Code (ESP32-C3 with Deep Sleep)

// Energy Harvesting PIR Sensor
#include <esp_sleep.h>

const int pirPin = 4;
const int wakePin = 5;
const int ledPin = 8;
const int batteryPin = 3;

RTC_DATA_ATTR int eventCount = 0;
RTC_DATA_ATTR unsigned long lastWakeTime = 0;

void setup() {
  Serial.begin(115200);
  
  pinMode(pirPin, INPUT);
  pinMode(ledPin, OUTPUT);
  
  esp_sleep_wakeup_cause_t wakeup_reason = esp_sleep_get_wakeup_cause();
  
  if (wakeup_reason == ESP_SLEEP_WAKEUP_EXT0) {
    digitalWrite(ledPin, HIGH);
    delay(500);
    digitalWrite(ledPin, LOW);
    eventCount++;
    sendNotification();
    lastWakeTime = millis();
  } else if (wakeup_reason == ESP_SLEEP_WAKEUP_TIMER) {
    reportBattery();
  }
  
  goToSleep();
}

void sendNotification() {
  Serial.print("Motion detected! Total events: ");
  Serial.println(eventCount);
  delay(100);
}

void reportBattery() {
  int raw = analogRead(batteryPin);
  float voltage = (raw / 4095.0) * 3.3 * 1.5;
  Serial.print("Battery voltage: ");
  Serial.println(voltage);
}

void goToSleep() {
  esp_sleep_enable_ext0_wakeup((gpio_num_t)pirPin, 1);
  esp_sleep_enable_timer_wakeup(24 * 60 * 60 * 1000000ULL);
  esp_deep_sleep_start();
}

void loop() {}

Power Budget Calculation

Component power consumption:

• PIR sensor (PYD 2597): 2 µA
• ESP32-C3 deep sleep: 5 µA
• LDO (MCP1700): 2 µA
• Total standby current: 9 µA

With 10 events/day: 0.216 mAh + 0.021 mAh = 0.237 mAh/day

With 1000 mAh battery: 1000 / 0.237 ≈ 4,200 days ≈ 11.5 years (battery self-discharge limits to 2-3 years)

Installation Steps

1. Assemble power management circuit on PCB or protoboard
2. Program ESP32 and test with motion detection
3. Measure standby current to verify it is under 10 µA
4. Mount components in weatherproof enclosure
5. Place solar panel facing south (northern hemisphere) at optimal angle
6. Deploy in field and test for 24 hours

Project Extensions

• Add LoRa radio to transmit motion events to a central receiver
• Add DS18B20 to report ambient temperature
• Use MQTT to send data to Home Assistant via Wi-Fi
• Create a network of solar-powered sensors for perimeter security
• Use PIR to wake a camera for wildlife photography

Conclusion

This energy-harvesting PIR sensor provides maintenance-free operation in remote locations. With proper design, it can operate indefinitely without battery changes.