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2.10 Detect Human Movement

In this lesson, we’ll learn how to use a Passive Infrared (PIR) sensor with the Raspberry Pi Pico 2 to detect human movement. PIR sensors are commonly used in security systems, automatic lighting, and other applications where motion detection is required. They detect infrared radiation emitted by warm objects, such as humans or animals, in their field of view.

What You’ll Need

In this project, we need the following components.

It’s definitely convenient to buy a whole kit, here’s the link:

Name	ITEMS IN THIS KIT	LINK
Newton Lab Kit	450+	Newton Lab Kit

You can also buy them separately from the links below.

SN	COMPONENT	QUANTITY	LINK
1	Raspberry Pi Pico 2	1	BUY
2	Micro USB Cable	1
3	Breadboard	1	BUY
4	Jumper Wires	Several	BUY
5	PIR Motion Sensor Module	1	BUY

Circuit Diagram

When the PIR module detects someone passing by, GP14 will be high, otherwise it will be low.

Note

The PIR sensor have two potentiometers:

• Sensitivity Adjustment: Controls the range of detection.

• Time Delay Adjustment: Controls how long the output remains HIGH after motion is detected.

For initial testing, turn both potentiometers counterclockwise to their minimum positions. This sets the sensor to its most sensitive and shortest delay settings, allowing you to observe immediate responses.

Wiring Diagram

Writing the Code

We’ll write a MicroPython program that uses an interrupt to detect motion and prints a message when motion is detected.

Note

• Open the 2.10_detect_human_movement.py from newton-lab-kit/micropython or copy the code into Thonny, then click “Run” or press F5.

• Ensure the correct interpreter is selected: MicroPython (Raspberry Pi Pico).COMxx.

import machine
import utime

# Initialize GP14 as an input pin
pir_sensor = machine.Pin(14, machine.Pin.IN)

def motion_detected(pin):
    print("Motion detected!")

# Set up an interrupt on the rising edge
pir_sensor.irq(trigger=machine.Pin.IRQ_RISING, handler=motion_detected)

# Main loop does nothing, interrupt handles motion detection
while True:
    utime.sleep(1)

When the code is running, you will observe the following phenomenon:

• Move in front of the PIR sensor.

• When motion is detected, “Motion detected!” should appear in the console.

Understanding the Code

1. Import Modules:

   • import machine: Access to hardware functions.

   • import utime: Time-related functions.

2. Initialize the PIR Sensor Pin:

   • pir_sensor = machine.Pin(14, machine.Pin.IN): Sets up GP14 as an input pin.

3. Define the Interrupt Handler:

   • def motion_detected(pin): Function that gets called when motion is detected.

   • print("Motion detected!"): Prints a message to the console.

4. Set Up the Interrupt:

   • pir_sensor.irq(trigger=machine.Pin.IRQ_RISING, handler=motion_detected): Configures an interrupt that triggers on the rising edge of the signal from the PIR sensor.

5. Main Loop:

   • while True: An infinite loop.

   • utime.sleep(1): The loop sleeps for 1 second in each iteration. The main loop doesn’t need to do anything because the interrupt handles the motion detection.

Example Code for Measuring Duration

You can modify the code to measure the duration of motion detection and the intervals between detections.

import machine
import utime

pir_sensor = machine.Pin(14, machine.Pin.IN)

last_trigger_time = utime.ticks_ms()

def pir_triggered(pin):
    global last_trigger_time
    current_time = utime.ticks_ms()
    duration = utime.ticks_diff(current_time, last_trigger_time)
    last_trigger_time = current_time

    if pir_sensor.value():
        print("Motion detected! Duration since last detection: {} ms".format(duration))
    else:
        print("Motion ended. Duration of motion: {} ms".format(duration))

# Set up interrupts for both rising and falling edges
pir_sensor.irq(trigger=machine.Pin.IRQ_RISING | machine.Pin.IRQ_FALLING, handler=pir_triggered)

while True:
    utime.sleep(1)

• Interrupts for Both Edges: set up the interrupt to trigger on both rising and falling edges using machine.Pin.IRQ_RISING | machine.Pin.IRQ_FALLING.

• Tracking Time:

  • Use utime.ticks_ms() to get the current time in milliseconds.

  • Calculate the duration between triggers to measure how long the PIR sensor output remains HIGH or LOW.

Practical Applications

• Security Systems: Detect intruders or unauthorized movement.

• Automatic Lighting: Turn lights on when motion is detected.

• Energy Saving: Power down devices when no movement is detected for a period.

Troubleshooting Tips

• False Triggers:

  • PIR sensors can be sensitive to environmental factors like temperature changes or sunlight.

  • Avoid pointing the sensor directly at heat sources or windows.

• Sensor Not Detecting Motion:

  • Ensure the sensor has had time to initialize (some sensors require up to 60 seconds).

  • Adjust the sensitivity potentiometer.

• Interference:

  • Keep the sensor away from electronics that may cause electromagnetic interference.

Conclusion

By integrating a PIR sensor with the Raspberry Pi Pico 2, you’ve added motion detection capabilities to your projects. Understanding how to read sensor inputs and handle interrupts allows you to create responsive and efficient programs.