Intelligent motion sensor
Security on construction sites, at events and other similar locations is a major challenge due to their large geographical size, difficulty in securing large and expensive assets and a lack of mains power to hardwire traditional security systems. ATF Services developed a range of solar powered surveillance cameras called Vision Intelligence to address the problem. As the range was developed, a Passive Infrared (PIR) sensor was needed to cover areas out of reach of the cameras, to improve night-time surveillance and to provide the option of waking up cameras when intruders are detected. The sensor also needed to wirelessly communicate with a site security system. When the company looked for a PIR sensor to complement its product family, nothing on the market did everything it wanted, so it approached Genesys to develop a custom solution.
The Vision Intelligence Motion Sensor senses movement and provides real time intruder notification via a smart phone app to multiple users, with no requirement for Wi-Fi connection. An anti-tamper switch and vibration sensor provides alerts to any interference with the sensor.
The device is designed to run off 4 x AA batteries for up to a year. A battery monitor and Bluetooth transceiver sends data to the App enabling it to show battery voltage status and warn of the need for battery replacements. The Bluetooth connectivity also facilitates onboarding and configuration of each new sensor into the system. A heartbeat monitor sends regular pulses to the system so that if any device becomes inoperable, the system knows immediately.
A key challenge in the design of the device was providing multiple communication options, particularly in a landscape of rapidly evolving communication options due to the rapid growth in Internet of Things technologies.
ATF Services had an existing range of cameras with connectivity to the internet. To enable cloud connection of the sensors via the cameras, the motion sensor design includes a TI15.4 frequency hopping 915 MHz RF connection option, which is a good option for networking devices in a star topology.
To enable standalone internet connectivity for sites where cameras are not installed, a Low Power Wide Area Network (LPWAN) option was required. The Sigfox network was chosen as the technology was being rolled out in Australia at the time but it was integrated via a plug-on board to enable cost effective upgrades. When a major telecommunication provider started rolling out the NB-IoT option for LPWAN, Genesys developed an NB-IoT plug-on module as an option for areas that did not have Sigfox coverage.
Another design challenge was ensuring the device could operate for up to a year with disposable batteries. In addition to the low power benefits of TI15.4, Sigfox and NB-IoT, the main power saving feature is a separate processor for handling motion detection. This means the main microcontroller is asleep most of the time. An algorithm also prevents “spamming” by detecting "normal" business activity and stops sending false-positive alerts. At the end of the working day, the system wakes itself up and start sending alerts again when it detects unusual activity. Due to the wide variety of climatic conditions the system can be deployed in, the battery life of the system was tested and characterised in both high and low temperatures.
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