Description

This project is an Internet of Things (IoT) RF wireless sensor that is retrofitted in existing smoke detector alarms and an RF-to-WiFi gateway to a cloud back-end that provides information about the state of the sensors. The solution is equally applicable to fire/smoke/CO2/gas sensor alarms. Upon activation event, the sensor in the smoke detector transmits a trigger signal to the gateway, which in turn notifies the back-end over a wireless internet connection so that a notification is immediately sent out to subscribers. Fast reaction to fire event is crucial, so an end-to-end time from detection to notification doesn't exceed 10 seconds. The notifications vary from e-mail, push notification on a smart device to SMS and possibly a phone call to a predefined number. Evacuation route may be included in the notification so that subscribers know how to reach the predefined gathering point. The gateway may send a notification to the fire department as well. The sensors also periodically send a 'heartbeat' signal and battery measurement to the gateway so that the end-user knows if a smoke sensor will require battery replacement soon, plus the back-end verifies that the connection sensor<>gateway is available. That feature makes it a more reliable solution, as at any point we have visibility over the sensor battery and wireless link state. Upon loss of wireless link with the gateway, the gateway sends a notification to the end user. Upon loss of connectivity of the gateway with the cloud back-end, the cloud sends a notification to the end user. By having a low power RF-enabled sensor node (433Mhz) retrofitted in the fire sensor we provide long (2+ years) battery life, plus a very important from a reliability point of view periodical (every 30 min) wireless link quality and battery state feedback that would not be possible using WiFi as it is power hungry. The sensor is equipped with a temperature sensor so it is capable of monitoring for sharp temperature increases prior to the smoke detector registering smoke and by doing so improving reaction times further. The sensor uses encrypted communications channel over a 433Mhz radio link to the gateway and is paired with the gateway so that no other nearby gateway can pick up the signals and send false notifications. Sensor wireless communication range is ~200m, making it ideal for covering of remotely located rooms. A gateway supports up to 16 wireless sensors (further extensible). Each sensor has a unique address so that upon activation it is known which sensor has triggered and the notification contains the name and address of the triggered sensor. The gateway communicates with the back-end using the popular MQTT protocol and over a TLS encrypted link. The gateway has a relay module that can be used to shut off the power supply, gas, water etc. and further reduce the risk of damage due to combined fire and gas explosion for example. Alternatively, the relay output can be used to trigger external GSM/FPRS/SIM card based notifier, this way making it independent of internet connection or acting as a redundant channel for event notification. The gateway code features watchdog, which guarantees it is operational at any point of time, and in the unlikely event of a crash, it is restarted automatically. The solution is cheap and easy to manufacture, with an estimated cost per sensor in the range 15-20 EUR. The gateway will cost roughly 35 EUR, making this solution quite affordable in terms of hardware. The back-end will require hosting fees, so a subscription model is proposed. A VPS (virtual private server) with microservices and front-end for up to 10000 connected gateways will cost less than 50 EUR per month and is easy to scale further. The installation consists of a simple sensor retrofit into existing smoke alarms and setting up the cloud gateway with WiFi credentials. By using wireless communication it is easy to incorporate this sort of solution into existing structures, no additional cabling is needed. The hardware prototypes are designed with CE certification requirements in mind for EMI and safety and are production ready.

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