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New Wireless IOT Sensor Layer for Home Environmental Monitoring System

This Instructable describes a lower-cost, battery-powered wireless IOT sensor layer for my earlier Instructable: LoRa IOT Home Environmental Monitoring System. If you haven’t already viewed this earlier Instructable, I recommend reading the introduction for an overview of the capabilities of the system which are now extended to this new sensor layer.
The original LoRa IOT Home Environmental Monitoring System achieved the objectives I had set out when it was published in April 2017. However, after using the monitoring system for a number of months to monitor temperature & humidity on each floor of the house, I wanted to add 11 more sensors at particularly vulnerable locations in the house; including, six sensors strategically placed in the basement, sensors in each bathroom, and a sensor in the attic, laundry, and kitchen.
Rather than add more LoRa based sensors from the earlier Instructable which are somewhat expensive and powered via AC adapters, I decided to add a layer of lower cost, battery operated sensors using 434-MHz RF Link Transmitters. To maintain compatibility with the existing LoRa IOT Home Environmental Monitoring System, I added a wireless bridge to receive the 434-MHz packets and retransmit them as LoRa packets at 915-MHz.
The new sensor layer consists of the following subsystems:
434-MHz Wireless Remotes - battery operated temperature and humidity sensors Wireless Bridge - Receives 434-MHz packets and retransmits them as LoRa packets.The 434-MHz Wireless Remotes use lower transmit power and less robust protocols compared with LoRa radios, so the Wireless Bridge location in the house is chosen to ensure reliable communication with all 434-MHz Wireless Remotes. Using the Wireless Bridge allows communication with the 434-MHz Wireless Remotes to be optimized without placing any constraint on where the LoRa IOT Gateway is located.
The 434-MHz Wireless Remotes and Wireless Bridge are built using readily available hardware modules and a few individual components. The parts can be obtained from Adafruit, Sparkfun, and Digikey; in many cases, Adafruit and Sparkfun parts are also available from Digikey. Competent soldering skills are needed to assemble the hardware, in particular, the point-to-point wiring of the 434-MHz Wireless Remotes. The Arduino code is well commented for understanding and to enable easy extension of functionality.
The objectives for this project included the following:
Find a lower cost wireless technology suitable for household environments. Develop a battery powered wireless sensor able to operate for a number of years on one set of batteries. Require no modification to the LoRa IOT Gateway hardware or software from my earlier Instructable.The total parts cost for the 434-MHz Wireless Remotes, excluding the 3xAA batteries, is $25, of which the SHT31-D temperature and humidity sensor accounts for more than half ($14).
As with the LoRa remotes from my earlier Instructable, the 434-MHz Wireless Remotes take temperature and humidity readings, and report to the LoRa IOT Gateway, via the Wireless Bridge, every 10 minutes. The eleven 434-MHz Wireless Remotes were put into operation in December 2017 using 3 x AA batteries nominally providing 4.5V. The battery readings from the eleven sensors in December 2017 ranged from 4.57V to 4.71V, sixteen months later in May 2019 the battery readings range from 4.36V to 4.55V. The use of parts with a wide operating voltage range should ensure operation of the sensors for another year or more, subject to maintaining RF link reliability as transmit power is reduced with lower battery voltages.
The reliability of the 434-MHz sensor layer has been excellent in my household environment. The new sensor layer is deployed across 4,200 SqFt of finished space and 1,800 SqFt of un-finished basement space. Sensors are separated from the Wireless Bridge by a combination of 2 - 3 interior walls and floor/ceilings. The LoRa IOT Gateway from my earlier Instructable sends an SMS Alert if communication is lost with a sensor for more than 60 minutes (6 missed ten minute reports). One sensor, on the floor in a corner at the far end of the basement behind stacked boxes, will cause a lost contact alert every now and then, however, in all cases communication with the sensor re-establishes without any intervention.”

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