Board and part

Arduino Nano PIR Sensor Simulator: Wiring, Code and a Live Circuit

This is an HC-SR501 PIR motion sensor wired to an Arduino Nano, 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

5 V logic
No library
OUT on pin 2
Powered from 5 V, 3.3 V output

Arduino Nano · 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 Arduino Nano

Three wires: VCC to 5V, GND, and OUT to pin 2. No library is needed.

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

PIR Sensor pin	Arduino Nano pin	Why
VCC	5V	The HC-SR501 takes 4.5 to 20 V and regulates it down to 3.3 V on board.
OUT	pin 2	A 3.3 V high while it sees motion, then low.
GND	GND	Common ground.

Power

The output is a 3.3 V high, which the Arduino Nano reads as HIGH: its threshold is half of 5 V. Nothing else is needed.

Pins to leave alone on the Arduino Nano

A6 and A7 are analog only: pinMode(A6, OUTPUT) does nothing and digitalRead(A7) is not there to call. D0 and D1 are the USB serial port.

On a real bench

The Nano plugs into the breadboard itself, straddling the center channel, so the PIR Sensor goes in a few columns along and every connection is a short jumper. The silkscreen labels its pins D2 to D13 and A0 to A7; in code D2 is simply 2. A Nano clone with a CH340 USB chip needs that driver on a real computer.

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 Arduino Nano pin 2

const int PIR_PIN = 2;   // OUT, pin 2
int lastState = LOW;

void setup() {
  Serial.begin(9600);
  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(9600) opens the serial monitor. Serial is the USB port, as on the Uno; a clone with a CH340 chip needs that driver on a real computer, which the simulator does not.

Pitfalls

Common mistakes with the PIR Sensor on the Arduino Nano

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.

Picking A6 or A7

A6 and A7 look like the other analog pins but are inputs to the ADC and nothing else. the PIR output on either of them never sees a digital level. Any of D2 to D13 or A0 to A5 works.

FAQ

Questions and answers

Can I simulate a PIR sensor with an Arduino Nano?

Yes. The circuit at the top of this page is an Arduino Nano with a HC-SR501 PIR sensor, running in your browser on a simulated ATmega328P. 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 3.3 V output enough for a 5 V board?

Yes. The Arduino Nano reads anything above 2.5 V as HIGH, and 3.3 V is comfortably above that.

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