Product Specs

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Exiting this particular sleeping state the E-RL 2 needs to be woken-up by a simple

button press on the side of the lock to start it advertising again during a set period. The

smartphone app will now be able to detect the advertising packets and act accordingly

depending on the relationship with the E-RL 2.

Figure 3.

In real-life situations smartphones (Central) will be surrounded by peripherals

broadcasting (Advertising) their presents, see Figure 3.

A master (or Central) is the BLE device that initiates an outgoing connection request

to an advertising peripheral device.

A slave (or Peripheral) is the BLE device which accepts an incoming connection

request after advertising.

A slave can only be connected to one master, but a master can be connected to

multiple slaves. In the smartwatch example, your iPhone can theoretically connect to

multiple smartwatches at the same time. However, your smartwatch can only ever

connect to one smartphone at a time.

There is no limit in the Bluetooth SIG on the number of slaves a master can connect to.

Generally this will be limited by the BLE technology or Bluetooth stack you use.

Devices such as smartphones or tablets would generally (but not exclusively) adopt the

role of “Scanner” and would “discover” other devices that have adopted the

“Advertiser” role by a process called discovery which can be active (“are there any

devices out there?”) or passive (“I’ll listen whilst devices advertise their presence”).

Devices that adopt the “Advertiser” role are generally (but not exclusively) smaller

footprint devices such as heart rate monitors or temperature sensors.

Once devices have discovered one another one will act as an “Initiator” (typically the

smartphone or tablet type device) and attempt to connect to one of the devices that it

has discovered. If successful it will adopt the role of “Master” and the other will adopt