ubluetooth — low-level Bluetooth

This module provides an interface to a Bluetooth controller on a board. Currently this supports Bluetooth Low Energy (BLE) in Central, Peripheral, Broadcaster, and Observer roles, and a device may operate in multiple roles concurrently.

This API is intended to match the low-level Bluetooth protocol and provide building-blocks for higher-level abstractions such as specific device types.

class BLE


class ubluetooth.BLE

Returns the singleton BLE object.



Optionally changes the active state of the BLE radio, and returns the current state.

The radio must be made active before using any other methods on this class.

BLE.config(param=value, ...)

Get or set configuration values of the BLE interface. To get a value the parameter name should be quoted as a string, and just one parameter is queried at a time. To set values use the keyword syntax, and one ore more parameter can be set at a time.

Currently supported values are:

  • 'mac': Returns the device MAC address. If a device has a fixed address (e.g. PYBD) then it will be returned. Otherwise (e.g. ESP32) a random address will be generated when the BLE interface is made active.
  • 'rxbuf': Set the size in bytes of the internal buffer used to store incoming events. This buffer is global to the entire BLE driver and so handles incoming data for all events, including all characteristics. Increasing this allows better handling of bursty incoming data (for example scan results) and the ability for a central role to receive larger characteristic values.

Event Handling

BLE.irq(handler, trigger=0xffff)

Registers a callback for events from the BLE stack. The handler takes two arguments, event (which will be one of the codes below) and data (which is an event-specific tuple of values).

The optional trigger parameter allows you to set a mask of events that your program is interested in. The default is all events.

Note: the addr, adv_data and uuid entries in the tuples are references to data managed by the ubluetooth module (i.e. the same instance will be re-used across multiple calls to the event handler). If your program wants to use this data outside of the handler, then it must copy them first, e.g. by using bytes(addr) or bluetooth.UUID(uuid).

An event handler showing all possible events:

def bt_irq(event, data):
    if event == _IRQ_CENTRAL_CONNECT:
        # A central has connected to this peripheral.
        conn_handle, addr_type, addr = data
    elif event == _IRQ_CENTRAL_DISCONNECT:
        # A central has disconnected from this peripheral.
        conn_handle, addr_type, addr = data
    elif event == _IRQ_GATTS_WRITE:
        # A central has written to this characteristic or descriptor.
        conn_handle, attr_handle = data
    elif event == _IRQ_GATTS_READ_REQUEST:
        # A central has issued a read. Note: this is a hard IRQ.
        # Return None to deny the read.
        # Note: This event is not supported on ESP32.
        conn_handle, attr_handle = data
    elif event == _IRQ_SCAN_RESULT:
        # A single scan result.
        addr_type, addr, connectable, rssi, adv_data = data
    elif event == _IRQ_SCAN_COMPLETE:
        # Scan duration finished or manually stopped.
    elif event == _IRQ_PERIPHERAL_CONNECT:
        # A successful gap_connect().
        conn_handle, addr_type, addr = data
        # Connected peripheral has disconnected.
        conn_handle, addr_type, addr = data
    elif event == _IRQ_GATTC_SERVICE_RESULT:
        # Called for each service found by gattc_discover_services().
        conn_handle, start_handle, end_handle, uuid = data
        # Called for each characteristic found by gattc_discover_services().
        conn_handle, def_handle, value_handle, properties, uuid = data
        # Called for each descriptor found by gattc_discover_descriptors().
        conn_handle, dsc_handle, uuid = data
    elif event == _IRQ_GATTC_READ_RESULT:
        # A gattc_read() has completed.
        conn_handle, value_handle, char_data = data
    elif event == _IRQ_GATTC_WRITE_STATUS:
        # A gattc_write() has completed.
        conn_handle, value_handle, status = data
    elif event == _IRQ_GATTC_NOTIFY:
        # A peripheral has sent a notify request.
        conn_handle, value_handle, notify_data = data
    elif event == _IRQ_GATTC_INDICATE:
        # A peripheral has sent an indicate request.
        conn_handle, value_handle, notify_data = data

The event codes are:

from micropython import const
_IRQ_CENTRAL_CONNECT                 = const(1 << 0)
_IRQ_CENTRAL_DISCONNECT              = const(1 << 1)
_IRQ_GATTS_WRITE                     = const(1 << 2)
_IRQ_GATTS_READ_REQUEST              = const(1 << 3)
_IRQ_SCAN_RESULT                     = const(1 << 4)
_IRQ_SCAN_COMPLETE                   = const(1 << 5)
_IRQ_PERIPHERAL_CONNECT              = const(1 << 6)
_IRQ_PERIPHERAL_DISCONNECT           = const(1 << 7)
_IRQ_GATTC_SERVICE_RESULT            = const(1 << 8)
_IRQ_GATTC_DESCRIPTOR_RESULT         = const(1 << 10)
_IRQ_GATTC_READ_RESULT               = const(1 << 11)
_IRQ_GATTC_WRITE_STATUS              = const(1 << 12)
_IRQ_GATTC_NOTIFY                    = const(1 << 13)
_IRQ_GATTC_INDICATE                  = const(1 << 14)

In order to save space in the firmware, these constants are not included on the ubluetooth module. Add the ones that you need from the list above to your program.

Broadcaster Role (Advertiser)

BLE.gap_advertise(interval_us, adv_data=None, resp_data=None, connectable=True)

Starts advertising at the specified interval (in microseconds). This interval will be rounded down to the nearest 625us. To stop advertising, set interval_us to None.

adv_data and resp_data can be any type that implements the buffer protocol (e.g. bytes, bytearray, str). adv_data is included in all broadcasts, and resp_data is send in reply to an active scan.

Note: if adv_data (or resp_data) is None, then the data passed to the previous call to gap_advertise will be re-used. This allows a broadcaster to resume advertising with just gap_advertise(interval_us). To clear the advertising payload pass an empty bytes, i.e. b''.

Observer Role (Scanner)

BLE.gap_scan(duration_ms[, interval_us][, window_us])

Run a scan operation lasting for the specified duration (in milliseconds).

To scan indefinitely, set duration_ms to 0.

To stop scanning, set duration_ms to None.

Use interval_us and window_us to optionally configure the duty cycle. The scanner will run for window_us microseconds every interval_us microseconds for a total of duration_ms milliseconds. The default interval and window are 1.28 seconds and 11.25 milliseconds respectively (background scanning).

For each scan result, the _IRQ_SCAN_RESULT event will be raised.

When scanning is stopped (either due to the duration finishing or when explicitly stopped), the _IRQ_SCAN_COMPLETE event will be raised.

Peripheral Role (GATT Server)

A BLE peripheral has a set of registered services. Each service may contain characteristics, which each have a value. Characteristics can also contain descriptors, which themselves have values.

These values are stored locally, and are accessed by their “value handle” which is generated during service registration. They can also be read from or written to by a remote central device. Additionally, a peripheral can “notify” a characteristic to a connected central via a connection handle.

Characteristics and descriptors have a default maximum size of 20 bytes. Anything written to them by a central will be truncated to this length. However, any local write will increase the maximum size, so if you want to allow larger writes from a central to a given characteristic, use gatts_write after registration. e.g. gatts_write(char_handle, bytes(100)).


Configures the peripheral with the specified services, replacing any existing services.

services_definition is a list of services, where each service is a two-element tuple containing a UUID and a list of characteristics.

Each characteristic is a two-or-three-element tuple containing a UUID, a flags value, and optionally a list of descriptors.

Each descriptor is a two-element tuple containing a UUID and a flags value.

The flags are a bitwise-OR combination of the ubluetooth.FLAG_READ, ubluetooth.FLAG_WRITE and ubluetooth.FLAG_NOTIFY values defined below.

The return value is a list (one element per service) of tuples (each element is a value handle). Characteristics and descriptor handles are flattened into the same tuple, in the order that they are defined.

The following example registers two services (Heart Rate, and Nordic UART):

HR_UUID = bluetooth.UUID(0x180D)
HR_CHAR = (bluetooth.UUID(0x2A37), bluetooth.FLAG_READ | bluetooth.FLAG_NOTIFY,)
UART_UUID = bluetooth.UUID('6E400001-B5A3-F393-E0A9-E50E24DCCA9E')
UART_TX = (bluetooth.UUID('6E400003-B5A3-F393-E0A9-E50E24DCCA9E'), bluetooth.FLAG_READ | bluetooth.FLAG_NOTIFY,)
UART_RX = (bluetooth.UUID('6E400002-B5A3-F393-E0A9-E50E24DCCA9E'), bluetooth.FLAG_WRITE,)
( (hr,), (tx, rx,), ) = bt.gatts_register_services(SERVICES)

The three value handles (hr, tx, rx) can be used with gatts_read, gatts_write, and gatts_notify.

Note: Advertising must be stopped before registering services.


Reads the local value for this handle (which has either been written by gatts_write or by a remote central).

BLE.gatts_write(value_handle, data)

Writes the local value for this handle, which can be read by a central.

BLE.gatts_notify(conn_handle, value_handle[, data])

Notifies a connected central that this value has changed and that it should issue a read of the current value from this peripheral.

If data is specified, then the that value is sent to the central as part of the notification, avoiding the need for a separate read request. Note that this will not update the local value stored.

BLE.gatts_set_buffer(value_handle, len, append=False)

Sets the internal buffer size for a value in bytes. This will limit the largest possible write that can be received. The default is 20.

Setting append to True will make all remote writes append to, rather than replace, the current value. At most len bytes can be buffered in this way. When you use gatts_read, the value will be cleared after reading. This feature is useful when implementing something like the Nordic UART Service.

Central Role (GATT Client)

BLE.gap_connect(addr_type, addr, scan_duration_ms=2000)

Connect to a peripheral.

On success, the _IRQ_PERIPHERAL_CONNECT event will be raised.


Disconnect the specified connection handle.

On success, the _IRQ_PERIPHERAL_DISCONNECT event will be raised.

Returns False if the connection handle wasn’t connected, and True otherwise.


Query a connected peripheral for its services.

For each service discovered, the _IRQ_GATTC_SERVICE_RESULT event will be raised.

BLE.gattc_discover_characteristics(conn_handle, start_handle, end_handle)

Query a connected peripheral for characteristics in the specified range.

For each characteristic discovered, the _IRQ_GATTC_CHARACTERISTIC_RESULT event will be raised.

BLE.gattc_discover_descriptors(conn_handle, start_handle, end_handle)

Query a connected peripheral for descriptors in the specified range.

For each descriptor discovered, the _IRQ_GATTC_DESCRIPTOR_RESULT event will be raised.

BLE.gattc_read(conn_handle, value_handle)

Issue a remote read to a connected peripheral for the specified characteristic or descriptor handle.

On success, the _IRQ_GATTC_READ_RESULT event will be raised.

BLE.gattc_write(conn_handle, value_handle, data, mode=0)

Issue a remote write to a connected peripheral for the specified characteristic or descriptor handle.

The argument mode specifies the write behaviour, with the currently supported values being:

  • mode=0 (default) is a write-without-response: the write will be sent to the remote peripheral but no confirmation will be returned, and no event will be raised.
  • mode=1 is a write-with-response: the remote peripheral is requested to send a response/acknowledgement that it received the data.

If a response is received from the remote peripheral the _IRQ_GATTC_WRITE_STATUS event will be raised.

class UUID


class ubluetooth.UUID(value)

Creates a UUID instance with the specified value.

The value can be either:

  • A 16-bit integer. e.g. 0x2908.
  • A 128-bit UUID string. e.g. '6E400001-B5A3-F393-E0A9-E50E24DCCA9E'.