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PIR motion sensor (HC-SR501)

Senses the warmth of a person moving, up to a few metres away: alarms and lights that turn on as you pass.

The test program

Test this part on its own before you build the rest: if it works alone, the rest is built on something you know works.

10 LED red, off
20 IF SENSOR("motion")=1 THEN LED red, on
30 WAIT 100
40 GOTO 10

What you should see: Wave a hand in front of the sensor: the red light comes on and stays on for a few seconds.

▶ Try it in the IDE

What to buy

  • PIR motion sensor (HC-SR501)

How to wire it to an ESP32-S3

  1. OUT → ESP32-S3: GPIO7
  2. VCC → ESP32-S3: 5V
  3. GND → ESP32-S3: GNDCommon ground: this link is mandatory.

If it does not work

The program runs but nothing happens
Just after power-up a PIR sensor needs about a minute to settle, and at 3.3 V it often does not work. Power it from 5 V, wait a minute without moving in front of it, then wave your hand.

What you can adjust

  • The two orange screws on the sensor: one sets the distance, the other how long it stays on.

Which boards it works on

  • ESP32-S3 Freenove: yes
  • Nordic nRF54LM20 DK: yes
  • Arduino UNO R4 WiFi: yes