Board and part

ESP32-C3 PIR Sensor Simulator: Wiring, Code and a Live Circuit

This is an HC-SR501 PIR motion sensor wired to an ESP32-C3 DevKitM-1, running live: the serial monitor says when motion starts and when it ends. In the editor, press the sensor to walk past it.

Run it in the editor Read the code

3.3 V logic
No library
OUT on GPIO 4
Powered from 5 V, 3.3 V output

ESP32-C3 · PIR Sensorlive0.000 s 0.00x

Click to open it in the editor

The circuit itself, running on the simulator with the sketch below. Press what can be pressed; click anything else to open it in the editor.

Connections

Wiring the PIR Sensor to the ESP32-C3

Three wires: VCC to 5V, GND, and OUT to GPIO 4. No library is needed.

Every connection in the circuit above, with the board’s own pin names.

PIR Sensor pin	ESP32-C3 pin	Why
VCC	5V	The HC-SR501 takes 4.5 to 20 V and regulates it down to 3.3 V on board.
OUT	GPIO 4	A 3.3 V high while it sees motion, then low.
GND	GND	Common ground.

Power

The module needs 5V for power, but its output is 3.3 V, so OUT connects straight to the ESP32-C3 with no divider. That makes the PIR one of the few 5 V modules that is a perfect match for a 3.3 V board.

Pins to leave alone on the ESP32-C3

GPIO 8 carries the onboard LED and GPIO 9 is the BOOT button, and both are also the default I2C pins. GPIO 2, 8 and 9 are strapping pins, and only GPIO 0 to 4 can read an analog voltage.

On a real bench

The ESP32-C3 DevKitM-1 is small enough to sit on one breadboard with room for the PIR Sensor beside it. Its USB port goes through a USB-to-serial chip; the cheaper SuperMini boards use the C3’s own USB, where Serial needs USB CDC on boot turned on in the IDE.

The sketch

The code, and what it does.

The sketch the circuit above runs. Open it in the editor, change a line and press Run: it compiles in your browser.

PIR sensor on ESP32-C3 GPIO 4

const int PIR_PIN = 4;   // OUT, GPIO 4
int lastState = LOW;

void setup() {
  Serial.begin(115200);
  pinMode(PIR_PIN, INPUT);
  Serial.println("Watching for motion");
}

void loop() {
  int state = digitalRead(PIR_PIN);
  if (state != lastState) {
    lastState = state;
    Serial.println(state == HIGH ? "Motion detected" : "Motion ended");
  }
  delay(50);
}

The PIR module does all the sensing itself; the board only reads one digital pin. OUT goes high when the infrared pattern in front of the lens changes, which is what a warm body moving does, and stays high for the hold time.

The sketch prints only changes, not every reading, by remembering the last state. That is the pattern for any sensor that holds a level: act on the edge, not the level.

Serial.begin(115200) opens the serial monitor. Serial is UART0, at 115200 baud in this sketch.

Pitfalls

Common mistakes with the PIR Sensor on the ESP32-C3

Not waiting for it to settle

A real HC-SR501 needs up to a minute after power-up to learn the room, and gives false triggers until then. Ignore it for the first 30 to 60 seconds.

The hold time knob

The orange trimmer next to the sensitivity one sets how long OUT stays high, from about 3 seconds to several minutes. A sensor that seems stuck on is usually turned all the way up. The simulated part has a hold property for the same thing.

Powering it from 3V3

Its regulator wants 4.5 V or more; at 3.3 V it triggers at random or not at all. Power from 5V; the output is already 3.3 V.

FAQ

Questions and answers

Can I simulate a PIR sensor with an ESP32-C3 DevKitM-1?

Yes. The circuit at the top of this page is an ESP32-C3 DevKitM-1 with a HC-SR501 PIR sensor, running in your browser on a simulated ESP32-C3 (RISC-V). Press the sensor on the drawing for motion; its hold and block times behave like the module’s. Press Run it in the editor to change the wiring or the code; it is free and needs no account.

Is the PIR output safe for the ESP32-C3?

Yes. The HC-SR501 is powered from 5 V but its output pin swings 0 to 3.3 V, exactly the board’s level.

What do the jumper positions H and L do?

H is repeat trigger: OUT stays high as long as motion keeps happening. L is single trigger: OUT goes low after the hold time even if motion continues, then can fire again. The part’s retrigger property chooses between them.

Can I use an interrupt for the PIR?

Yes, OUT is a clean digital edge with no bounce, so attachInterrupt() on RISING works well. Polling every 50 ms as here is just as good for a person walking past.

Build your own PIR Sensor project

Open this circuit in the editor, change the wiring or the code, and keep your version in a free account.

Start building free Open the editor