Mob.Bt (mob v0.6.6)

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Bluetooth Classic (BR/EDR) — device-level discovery, pairing, and cross-profile session management.

Profile-specific operations live in submodules:

  • Mob.Bt.Hfp — Hands-Free Profile (audio + vendor AT commands). Use this for headsets, PTT-equipped earpieces, etc.
  • Mob.Bt.Spp — Serial Port Profile (RFCOMM byte streams). Use this for legacy serial-over-Bluetooth devices (Arduino HC-05, OBD-II readers, marine GPS, industrial sensors).
  • Mob.Bt.Hid — Human Interface Device (input reports). Use this for Bluetooth keyboards, mice, gamepads, finger PTTs.

API style

Same as the rest of Mob: callbacks return socket unchanged, results arrive in handle_info/2 as 4-tuples:

{:bt, event_atom, session_id_or_nil, payload}

Discovery / pairing events use nil for session_id; profile events carry the session_id returned from the matching connect/2.

Permissions

Bluetooth requires runtime permissions on Android 12+ (API 31+):

Request via Mob.Permissions.request/2 before calling Mob.Bt functions.

iOS

Bluetooth Classic on iOS requires Apple's MFi (Made for iPhone) certification — a paid, NDA-gated program. Mob.Bt is Android-only. All functions return {:error, :unsupported} synchronously on iOS. For iOS-equivalent custom-hardware connectivity, use Mob.Ble.

Pairing flow

Two pairing modes, auto-selected by whether :pin is given:

# System UI flow — Android shows a system pairing dialog
socket = Mob.Bt.pair(socket, device)

# Programmatic — PIN supplied via API, no UI
socket = Mob.Bt.pair(socket, device, pin: "0000")

If the programmatic PIN fails or the device requires UI confirmation (e.g. numeric comparison), Android falls back to the system UI automatically.

Disconnect

One canonical disconnect for any profile session:

Mob.Bt.disconnect(socket, session_id)

The framework looks up which profile owns the session_id and routes to the right profile-disconnect internally. Emits a profile-specific event ({:bt, :hfp_disconnected, ...} etc).

Summary

Types

device()

A discovered or paired Bluetooth device.

session_id()

An opaque session identifier for an active profile connection.

Functions

cancel_discovery(socket)

Cancel an in-progress discovery.

disconnect(socket, session_id)

Disconnect a profile session by session_id.

list_paired(socket)

List currently paired (bonded) Bluetooth devices.

pair(socket, device, opts \\ [])

Pair (bond) with a Bluetooth device.

start_discovery(socket)

Begin Bluetooth Classic discovery. Discovered devices arrive as individual {:bt, :device_discovered, nil, device} messages, terminated by {:bt, :discovery_finished, nil, nil}.

unpair(socket, device)

Remove an existing pairing (bond).

Types

device()

@type device() :: %{
  :address => String.t(),
  :name => String.t(),
  optional(:bond_state) => :none | :bonding | :bonded,
  optional(:device_class) => non_neg_integer(),
  optional(:uuids) => [String.t()]
}

A discovered or paired Bluetooth device.

session_id()

@type session_id() :: pos_integer()

An opaque session identifier for an active profile connection.

Functions

cancel_discovery(socket)

@spec cancel_discovery(socket :: term()) :: term()

Cancel an in-progress discovery.

disconnect(socket, session_id)

@spec disconnect(socket :: term(), session_id()) :: term()

Disconnect a profile session by session_id.

Works for any profile (Mob.Bt.Hfp, Mob.Bt.Spp, Mob.Bt.Hid) — the framework dispatches internally based on which profile owns the session.

Emits a profile-specific disconnect event:

  • {:bt, :hfp_disconnected, session_id, reason}
  • {:bt, :spp_disconnected, session_id, reason}
  • {:bt, :hid_disconnected, session_id, reason}

list_paired(socket)

@spec list_paired(socket :: term()) :: term()

List currently paired (bonded) Bluetooth devices.

Result arrives as {:bt, :paired_devices, nil, [device]}.

pair(socket, device, opts \\ [])

@spec pair(socket :: term(), device(), keyword()) :: term()

Pair (bond) with a Bluetooth device.

Without :pin, Android shows the system pairing dialog (user enters PIN). With :pin, attempts programmatic pairing using the supplied PIN; falls back to system UI if the device demands user confirmation.

Result arrives as one of:

  • {:bt, :pair_succeeded, nil, device}
  • {:bt, :pair_failed, nil, %{device: device, reason: atom()}}

start_discovery(socket)

@spec start_discovery(socket :: term()) :: term()

Begin Bluetooth Classic discovery. Discovered devices arrive as individual {:bt, :device_discovered, nil, device} messages, terminated by {:bt, :discovery_finished, nil, nil}.

Discovery typically runs ~12 seconds on Android.

unpair(socket, device)

@spec unpair(socket :: term(), device()) :: term()

Remove an existing pairing (bond).

Result: {:bt, :unpaired, nil, device}.