Bidirectional Movement Detector
Writer: Innovations Team - Sensirion AG / June, 2017
Persons and objects cause air turbulences when moving around. A flow sensor can detect the direction of such air turbulences. Thus, it is possible to determine the direction of movement of persons and objects passing by the air flow sensor. This valuable information can be used to drive actions for building control or surveillance purposes. A smart home might turn on lightning in the direction of detected movement. A smart thermostat might increase or decrease temperature based on room occupancy and load.
Sensirion's flow sensor is a semiconductor MEMS version of the traditional hot wire anemometer. The sensing principle is based on thermal conductivity through the gas flowing over the sensor surface (figure 1).
In opposition to diaphragm based differential pressure sensors, Sensirion's CMOSens flow sensor characteristic shows high sensitivity especially at low air flows (figure 2). This allows to reliably measure ultra low flows and differential pressures.
A Sensirion flow sensor was attached to a doorway (figure 3, 4). Air movement was generated by a person entering and leaving the room. The sensor output was logged with Sensirion's EK-P3 Evaluation Kit.
The measurement result demonstrates that Sensirion's air flow sensor can be used as movement detection sensor (figure 4-8). A person moving slowly or quickly is detected by the air flow sensor attached to the doorway.
The event of an opening or closing door is also detected by its generated air turbulence (figure 9, 10).
- Sensirion flow sensor detects slow and quick moving persons passing through a doorway
- Direction of movement is detectable
- Closing and opening of doors is detectable
- Good signal-to-noise
This paragraph should give in a how to style how to build the solution for the own purposes.
To build an own movement detection sensor a Sensirion differential pressure sensor SDP6xx series (figure 12) can be sourced from distributors listed on the Sensirion website.
By careful breaking the inner plastic ring seal from the sensor's backside, the sensor chip is uncovered (figure 12-15).
Communicate with the digital sensor over I2C according to the explanations in the SDP600 series data sheet.