PIR Sensor Output Types: Digital vs Analog Explained

The Basics: What Comes Out of a PIR Sensor?

At its core, a PIR sensor element (the pyroelectric detector) produces an extremely small analog voltage signal when exposed to changing infrared radiation. This raw signal is typically measured in millivolts and requires significant amplification and processing before it can be useful.

The difference between digital and analog PIR sensors lies in how much of this processing is built into the sensor module itself.

Digital Output PIR Sensors

How They Work

Digital PIR sensors integrate all signal processing circuitry on the module. They take the raw analog signal from the pyroelectric element, amplify it, filter it, compare it to a threshold, and output a simple HIGH or LOW logic level.

Characteristics

• Output Signal: Binary (0V or VCC)
• Typical Examples: HC-SR501, HC-SR505, AM312
• Advantages: Extremely easy to use, no additional components, built-in hysteresis, consistent behavior.
• Disadvantages: Limited information, fixed timing, cannot distinguish motion type, no access to raw signal.

When to Use Digital Sensors

• Simple motion detection
• Beginner projects
• Battery-powered devices (low power)
• Quick prototyping

Analog Output PIR Sensors

How They Work

Analog PIR sensors provide access to the amplified but unprocessed signal from the pyroelectric element. Some may include basic filtering but output a continuous voltage that varies with the infrared energy received.

Characteristics

• Output Signal: Continuous analog voltage (0-3.3V or 0-5V)
• Typical Examples: IRA-E700 series, some LHI series
• Advantages: Rich information, can distinguish motion direction, enables people counting, allows advanced processing.
• Disadvantages: Requires ADC, more complex programming, susceptible to noise, higher power consumption.

When to Use Analog Sensors

• People counting systems
• Direction detection
• Research and development
• Occupancy estimation

Technical Deep Dive

Digital Output Signal Characteristics

A typical digital PIR sensor output follows this pattern:

1. Idle state: Output LOW (0V)
2. Motion detected: Output transitions to HIGH (VCC)
3. Hold time: Output remains HIGH for preset duration
4. Restore: Output returns to LOW until next detection

Analog Output Signal Characteristics

An analog PIR sensor output might show:

• Baseline noise: ~10-50mV fluctuations
• Motion signature: Characteristic waveform as person moves through zones
• Positive and negative swings due to dual-element design
• Frequency content typically 0.1-10Hz for human motion

Interfacing Examples

Reading a Digital Sensor (Arduino)

int pirPin = 2;
void setup() {
  pinMode(pirPin, INPUT);
  Serial.begin(9600);
}
void loop() {
  int motion = digitalRead(pirPin);
  if (motion == HIGH) {
    Serial.println("Motion detected!");
  }
  delay(100);
}

Reading an Analog Sensor (Arduino)

int analogPin = A0;
int threshold = 100;
void setup() {
  Serial.begin(115200);
}
void loop() {
  int sensorValue = analogRead(analogPin);
  int motionStrength = abs(sensorValue - 512);
  if (motionStrength > threshold) {
    Serial.print("Motion strength: ");
    Serial.println(motionStrength);
  }
  delay(50);
}

Making the Choice

Ask yourself: Do I just need to know if someone is there? → Digital sensor.
Do I need to count how many people pass? → Analog sensor.
Is this battery-powered? → Digital sensor.
Am I doing research? → Consider analog.