Learnwithsteem : Teaching robotics using the ESP32 board - Fourth lesson

HC-SR501 motion sensor :

The HC-SR501 sensor has 3 pins as shown in the following figure :

HC-SR50 Pins	To connect to
VCC	ESP32 5V
OUTPUT	Any ESP32's input Pin
GND	ESP32 GND Pin 0V

This infrared sensor can be configured by its user. For this, it has two potentiometers to adjust the detection distance and the duration of the high state. There is also the possibility of configuring it in two operating modes thanks to a jumper to be placed between two pins.

Components Required :

To complete the assembly, you will need the following parts:

• LED
• Connecting wires
• Breadboard
• ESP32 development board
• PIR motion sensor (HC-SR501)

How to perform the assembly on the breadboard?

To carry out the assembly, we connect:

• The 5V power supply (or 3.3V depending on the model of the sensor) of the ESP32 card goes to the VCC pin of the sensor.
• The GND pin of the ESP32 board goes to the GND pin of the sensor.
• Pin D13 of the ESP32 board goes to the Output pin of the
  sensor.
• The D14 pin of the ESP32 board goes to the anode (+) pin of the
  led diode and resistor.

Note: You can use all GPIOs as interrupts, except GPIO6 to GPIO11.

You can always consult the ESP32 pinout reference guide to know the location of each pin, for that I always provide you with this guide:

_{ESP32 Pinout Reference Guide}

_{Assembly simulation using Fritzing software}

Coding :

Start by launching the Thonny editor and Open a new file and then copy the following code :

    from machine import Pin
    from time import sleep

    motion = False

    def handle_interrupt(pin):
          global motion
          motion = True
          global interrupt_pin
          interrupt_pin = pin 

     led = Pin(12, Pin.OUT)
     pir = Pin(14, Pin.IN)

     pir.irq(trigger=Pin.IRQ_RISING, handler=handle_interrupt)

     while True:
           if motion:
                   print('Motion detected! Interrupt caused by:', interrupt_pin)
                   led.value(1)
                   sleep(10)
                   led.value(0)
                   print('Motion stopped!')
                   motion = False

To define the pins we always import the class of the module machine, also to define method timeouts we import the module time.

    from machine import Pin
    from time import sleep

Initialize a global variable named motion to False which will indicate the absence of detected motion.

    motion = False

Then introduce the function handle_interrupt. which is called at each detected movement in which the variable motion will take the value True.

    def handle_interrupt(pin):
          global motion
          motion = True
          global interrupt_pin
          interrupt_pin = pin 

Create two Pin objects, one for the LED on GPIO 12, and another for the PIR motion sensor on GPIO 14.

       led = Pin(12, Pin.OUT)
       pir = Pin(14, Pin.IN)

Set an interrupt on the pir by calling the irq() method.

       pir.irq(trigger=Pin.IRQ_RISING, handler=handle_interrupt)

Every time motion is detected, we light up an LED for 10 seconds.

     while True:
           if motion:
                   print('Motion detected! Interrupt caused by:', interrupt_pin)
                   led.value(1)
                   sleep(10)
                   led.value(0)
                   print('Motion stopped!')
                   motion = False

The realization of assembly and the execution in image:

• Prepare all the necessary equipment:

• Start by connecting the HC-SR501 sensor , led and resistor to the breadboard and then use the wires to link its pins with the pins of ESP32.

• The LED should light up for 10 seconds when motion is detected, and a message should be printed in the Shell.

• After 10 seconds, the LED turns off.

• You should see the following output on the shell :

Thank you for your follow and see you in the next part.