The AM312 is an ultra-miniature passive infrared (PIR) motion sensor module that detects movement by sensing changes in infrared radiation emitted by warm bodies passing within its field of view. Unlike larger PIR modules, the AM312 packs all its sensing and processing electronics directly into the sensor housing itself, producing a simple digital output with no external support circuitry required.
This makes the AM312 ideal for applications where size and power budget matter, such as battery-powered motion sensor nodes, wearables, security systems, automated lighting, and compact IoT devices. Its tiny footprint, very low quiescent current, and self-contained design have made it a popular low-power alternative to bulkier PIR modules.
What is AM312?
The AM312 is a digital intelligent PIR sensor with all electronic circuitry built directly into the small can-shaped detector housing. Only a power supply and any necessary power-switching components need to be added externally to form a complete motion-detection circuit — there is no separate control IC or adjustment potentiometers like on larger PIR modules.
Inside, a pyroelectric sensing element generates a small electrical charge whenever it detects fluctuating infrared energy crossing its field of view. This signal is amplified and processed entirely within the module, which then drives a digital output HIGH when motion is detected and LOW when the area is clear.
Design note: The AM312 is built around a similar pyroelectric sensing principle to larger PIR modules, but in a far more compact, fully self-contained package — there is no exposed BISS0001-style IC or external sensitivity/delay potentiometers to adjust.
AM312 overview
| Parameter | Value |
|---|---|
| Sensor Type | Passive Infrared (PIR) Motion Sensor |
| Output Type | Digital (HIGH/LOW) |
| Supply Voltage | 2.7V – 12V (DC) |
| Output Voltage (triggered) | ~3.3V |
| Output Voltage (untriggered) | 0V |
| Static/Quiescent Current | ~8–100µA (model/source dependent) |
| Trigger Hold Time | ~2–4 seconds (fixed) |
| Detection Angle | ~100° cone |
| Detection Range | ~3 meters |
| Operating Temperature | −20°C to +80°C |
| PCB Dimensions | ~8.5 × 10mm |
| Overall Length (with sensor) | ~27.2mm |
| Compatible Boards | Arduino, ESP32, Raspberry Pi |
Pinout
The AM312 ships as a tiny pre-assembled module — a small can-shaped pyroelectric sensor mounted on an even smaller PCB. It is one of the most compact PIR modules available and uses a simple 3-pin interface.
3-pin pinout
| Pin | Name | Type | Description |
|---|---|---|---|
| 1 | VCC | Power | Power supply input — accepts roughly 2.7V to 12V DC |
| 2 | OUT | Output | Digital output — goes HIGH (~3.3V) when motion is detected, LOW (0V) when idle |
| 3 | GND | Power | Ground connection |
No adjustments available: Unlike larger PIR modules, the AM312 has no onboard sensitivity or delay potentiometers and no trigger-mode jumper. The detection range, delay time, and trigger behavior are fixed by the internal design and cannot be tuned externally — any timing or sensitivity adjustments must be handled in software on the host microcontroller.
Working principle
PIR stands for Passive Infrared. The AM312 detects changes in infrared radiation across its field of view and produces an electrical output signal in response, without emitting any radiation of its own — it is purely passive, reacting only to infrared already present in the environment, such as body heat.
A small lens on the front of the module focuses incoming infrared light from a roughly 100° cone onto the internal pyroelectric element. As a warm body moves across this field of view, the infrared level falling on the element fluctuates. This fluctuation generates a tiny electrical signal, which is amplified and processed entirely by circuitry built into the same small housing — there’s no separate signal-conditioning IC sitting beside it on the board.
Output behavior: When valid motion is detected, the OUT pin goes HIGH and stays high for a fixed hold time (commonly cited around 2–4 seconds depending on the specific unit), after which it returns LOW if no further motion is detected. Continued motion within the hold window keeps the output HIGH.
Power-on stabilization: Like other PIR sensors, the AM312 needs a brief warm-up period after power is first applied — often cited as around one minute — during which the internal circuitry stabilizes to the surrounding infrared environment before producing reliable readings.
AM312 module construction
Pyroelectric Sensing Element A small can-shaped pyroelectric crystal sits at the front of the module behind a built-in lens. It generates a tiny electrical charge in response to changes in infrared radiation across its field of view, forming the core sensing component.
Integrated Lens Unlike the large external Fresnel dome used on bigger PIR modules, the AM312’s lens is built directly into the small sensor can itself, focusing infrared light from its ~100° detection cone onto the pyroelectric element while keeping the overall package extremely compact.
Onboard Amplifier and Signal Processing All amplification and signal-conditioning circuitry needed to convert the weak pyroelectric charge into a clean digital output is integrated into the sensor housing or the small adjoining PCB — there is no separate exposed control IC as found on larger modules.
Onboard Voltage Regulator Most AM312 modules include a small low-dropout (LDO) regulator, allowing the module to accept a wide input range while internally running its sensing element at its required lower voltage. Decoupling capacitors on both the regulator input and output filter supply noise.
Output Current-Limiting Resistor A small series resistor on the output line limits the current the OUT pin can source or sink, protecting the internal circuitry when driving a microcontroller input directly.
Specifications
Key specifications of the AM312 PIR motion sensor are listed below.
| Parameter | Value |
|---|---|
| Supply Voltage | 2.7V – 12V DC |
| Output Voltage (HIGH) | ~3.3V |
| Output Voltage (LOW) | 0V |
| Quiescent Current | ~8µA (low-power variants) up to ~0.1mA (general spec) |
| Active Current | Low single-digit mA range |
| Trigger Hold Time | ~2–4 seconds, fixed |
| Detection Angle | ~100° cone |
| Detection Range | ~3 meters |
| Operating Temperature | −20°C to +80°C |
| Sensing Element | Pyroelectric infrared sensor |
| Adjustability | None — fixed sensitivity and delay |
| PCB Dimensions | ~8.5 × 10mm |
| Package | Miniature can-style sensor on small PCB |
Helpful Resources
- Download the datasheet: here
- AM312 with Arduino
- AM312 with ESP32
- AM312 with Raspberry Pi