Minimum supported version is Bluetooth 4.0 from 2010, also known as Bluetooth LE (Bluetooth Low Energy). Following are all supported Bluetooth versions:
Bluetooth 4.0 - Bluetooth Low Energy
Bluetooth 4.1 - direct IoT connection
Bluetooth 4.2 - direct IPv6 connection
Bluetooth 5.0 - higher speed longer range
Bluetooth 5.1 - direction finding
Bluetooth 5.2 - improved audio
Bluetooth 5.3 - better signal quality and security
In locations where access to 5V is challenging, traditional Bluetooth Beacons can be used to provide a Static (broadcasting a signal that changes LESS than once every year) bluetooth signals.
Daxia DX-CP28
The DX-CP28 has dual batteries for up to 5 years operation (actual figure depends on broadcast settings and batteries used).
Note most CR2477 batteries now has 1000 mAh instead of 880 mAh.
Holyiot 23006
The 23006 has dual batteries for up to 5 years operation (actual figure depends on broadcast settings and batteries used) and also a waterproof rating.
Out of the 40 Bluetooth LE channels, 3 are used for advertising signals (despite their consective numbering the channels 37, 38, 39 are actually NOT next to each other)
Many companies (e.g. Apple) advertises on all 3 channels at once to increase chance of the signal getting detected.
Setting of Bluetooth Advertising Interval, Scan Interval and Scan Window is important, as they must overlap for discovery to happen (those tall dotted boxes shown in diagram below).
The Advertising Interval can be set from 20ms to 10.24 seconds (in steps of 0.625ms) with random delay from 0ms to 10ms added.
Sensor Station
Scan Duration
For Sensor Stations with mains power supply the bluetooth scan defaults for performing scanning are:
Scan Duration: 10s
Scan Interval: 211ms
Scan Window: 120ms
You can increase the Window value to closer to the Interval value to improve detection coverage BUT that will use more power and take away airtime from the WiFi module sharing the 2.4G radio.
Interval size of 211 is a prime number to avoid keep on missing some advertisements made on even intervals.
Signal Strength
Some Sensor Station operating system (e.g. esphome) displays the signal strengths as graphics (colour bars) instead of actual dB values, we have converted those 4 graph times (which are 4 dB ranges) into 4 exact dB values:
Bluetooth 5.1 direction finding is very nice, by attaching Constant Tone Extension (CTE) data sequence behind the CRC in a Bluetooth packet in order to get Angle of Departure (AoD) or Angle of Arrival (AoA) with multiple antennas at either transmitter or receiver.
That would be great for our indoor positioning, unfortunately it is not readily available yet, so we will be using the Received Signal Strength Indication (RSSI) and triangulation from multiple fixed Bluetooth sources instead.
Personal Console uses the mobile phone to scan for emitted bluetooth signals to determine current position. It is also possible to do it the other way round - use other nearby Bluetooth devices to scan for bluetooth signals emitted by the the mobile phone.
This way is NOT receommneded, as we believe our way is substantially more private, however it is interesting to know there are alternatives available:
Apple iOS devices will NOT show the owner the Bluetooth MAC addresses of surrounding devices, if some day they unlock your data (data that you have collected with your own resources on your own device) then you can use the Bluetooth MAC address directly as Activity Marker original design.
Cup Compute
On most device the Bluetooth MAC Addresses can be set to broadcast an Activity Marker instead of its default Bluetooth MAC address.
For the popular Cup Compute, the Bluetooth MAC address can be changed in the firmware, there is no direct support for that in esphome yet, but that feature can be added easily.
Apple blocks its iphone customers from accessing the WiFi and Bluetooth MAC addresses that they collected themselves on their own phone in their own environment.
Until Apple removes that block, their customers need to use other bluetooth broadcast signals (e.g. Apple's ibeacon signal which will be our initial focus).
