PIR Sensor with I2C Interface: Digital PIR Sensors

Introduction

Traditional PIR sensors output an analog voltage or a simple digital pulse. Newer digital PIR sensors integrate amplification, ADC, and digital logic, offering I2C interface for configuration and readout.

Advantages of Digital PIR Sensors

• Programmable parameters: Sensitivity, threshold, timing can be set via software.
• On-chip processing: Some perform motion classification (human vs. pet).
• Multi-sensor support: Multiple sensors on same I2C bus.
• Status registers: Read motion flags, signal strength, fault conditions.
• Lower power modes: Wake-on-motion with interrupt output.

How They Work

A digital PIR sensor contains:

1. Pyroelectric sensing element(s).
2. JFET buffer or op-amp.
3. Programmable gain amplifier (PGA).
4. Analog-to-digital converter (ADC).
5. Digital signal processor (DSP) with motion detection algorithm.
6. I2C interface and control registers.
7. Interrupt output (INT) for wake-up.

Example: Panasonic EKMB with I2C

Panasonic’s EKMB series includes digital versions with I2C interface. Features:

• Selectable sensitivity (through registers).
• Motion detection flag.
• Signal level readout (for advanced processing).
• 1-6 µA power consumption.
• I2C address configurable.

Example: Excelitas PYD 2597 (1-Wire)

The PYD 2597 uses a proprietary 1-wire digital interface, not I2C. It allows:

• Motion detection with interrupt.
• Configuration of detection parameters.
• Ultra-low power (2 µA).

Example: InfraTec digital pyroelectric detectors

InfraTec offers digital pyroelectric detectors with I2C for gas sensing applications.

I2C Communication Protocol

Typical register map:

• Register 0x00: Status (motion detected, fault).
• Register 0x01: Configuration (sensitivity, threshold).
• Register 0x02: Timing (hold time, block time).
• Register 0x03: Signal level (raw ADC value).

// Example I2C read (pseudocode)
write_i2c(device_addr, 0x00); // Select status register
status = read_i2c(device_addr);
if (status & 0x01) {
    // Motion detected
}

Interrupt Output

The INT pin can be configured to assert when motion is detected, allowing the microcontroller to sleep until an event occurs.

Advantages over Traditional PIR

• No external ADC needed.
• Simpler PCB layout (no analog signal routing).
• Configurable in firmware (no potentiometers).
• Diagnostic information available.

Disadvantages

• Higher cost.
• More complex programming.
• May consume slightly more power than the lowest-power analog sensors.

Applications

• IoT sensors where configuration flexibility is needed.
• Multi-sensor arrays (shared I2C bus).
• Products requiring calibration and tuning.

Conclusion

Digital PIR sensors with I2C interface offer flexibility and advanced features at a modest cost increase. They are ideal for designs where software configurability is valuable.