This section covers topics that might affect your sensor deployment as well as some basic best practices.
To pair sensors to the BuildAX LRS it must first be put into Pairing Mode. To do this, hold the button on the rear of the device until the lights flash alternately. The LRS will stay in pairing mode for a period of 5 minutes.
What is "Pairing"?
The BuildAX sensors broadcast data packets containing information about their environment over the air. This data could potentially be used by eavesdroppers to infer whether a building is occupied, something existing systems have typically not addressed. As a security measure, all BuildAX sensors use 128-bit AES encryption to prevent packets being read while in transmission.
To decrypt data from the sensors, the LRS must know the key which was used to encrypt it. An encryption key is transmitted from the sensor to the LRS when the button on the rear of the sensor (see #2 on the hardware diagram) is pressed. The radio broadcast power is set to the minimum on the sensor, to limit the range at which the packet can be received.
The LRS then stores the unique key for the sensor in the
file on the SD card. To instruct the LRS to listen for keys, it must be put
into "Pairing Mode", by pressing the button on the rear of the device.
Note: The LRS will log packets from BuildAX sensors regardless of whether it has received an encryption packet, as these may be decrypted at a later date and would otherwise be lost.
ENV Sensor Deployment
ENV Sensor Range
The achievable range of the sensors will depend on a number of factors, including the materials used in the construction of the building, the thickness of the walls, and the "noise-floor" of your deployment environment.
If there are a lot of devices transmitting on the same 433MHz band as the sensors (for example, in a city environment) the radio frequency will be noisier and the sensors will not be "heard" by the LRS at further distances.
Tips on deploying sensors in a building:
- Position the LRS at a central location, so as to be in range of all sensors.
- Air temperature and humidity in a room are stratified (change based on height).
- The PIR lens is directional. Mount sensors on the wall vertically if this is important.
- If a sensor at the limit of its range, try upping the transmission interval.
- Walls appear "thicker" when the radio signal has to travel through them diagonally.
- Try to avoid direct sunlight when attaching sensors to surfaces. This will skew the data they generate.
- Also remember the position of the Sun will change throughout the day!
Note also that the battery life of the ENV sensor will be lower on average in high-traffic areas, as a data packet will be transmitted every time the PIR sensor is triggered.
Handling Sensors: Note that after handling the ENV sensors, the humidity/temperature reading will be biased by the temperature of your hands. This will settle again after 5 minutes or so.
A sensor's signal strength is indicated by its RSSI value (Received Signal Strength Indication). This can be thought of as the "loudness" of the radio signal and is measured in dBm.
RSSI values can be found in the web interface (see the Live Data page), or in the 4th column of the CSV-format data available as a file, or over the various streaming interfaces (telnet, serial, websocket).
Signal strength will be affected by the battery level of the sensor, the distance from the LRS, and any obstacles which the signal has to travel through in-between.
All environments will have a certain amount of potential noise present in the radio spectrum used by the BuildAX sensors. This level of noise is referred to as the noise "floor", and sensors transmitting must be "louder" than this background noise level in order to be heard.