To implement a BLE advertise-only beacon, the device has to transmit a
non-connectable unidirectional advertising package as defined in the
This type of advertising packet signals to scanning (master) devices
that this device does not support a complete BLE data connection but
can only broadcast information. The advertising packet contains the MAC
address (6 octets using IEEE format) of the device sending the
information and a data payload of up to 31 octets. This broadcasting
information may contain device ID, sensor readings, TX power level,
battery level, etc. To ensure compatibility between all BLE devices and
support proper interpretation of the received data, the BLE
specification defines the required advertising data format, which
includes a tag for manufacturer-specific information that allows
embedding proprietary data into a standardized advertising format. More
information on the BLE advertising payload structure may be found in an earlier article (Galeev, "Make the most of Bluetooth LE advertising mode" ).4
The EM9301 BLE Controller from EM Microelectronic,5
integrates a 2.4-GHz radio and a BLE controller that handles
specification-compliant packet assembly, transmission timing, and RF
channel management. As a fully functional BLE controller, EM9301
supports all modes of operation for both master and slave types of
devices and communicates with any number of host microcontrollers, which
contain the upper layers of the BLE stack, via a standard peripheral
interface (SPI) bus using standardized Host Controller Interface (HCI)
In the simplest case of an advertise-only BLE device, the advertising
mode can be fully implemented with just three HCI commands; setting the
data for the advertising payload, configuring the time interval between
advertising packets (up to 10 seconds), and requesting the controller to
start a periodic advertising broadcast.
The critical selection criteria for a BLE beacon MCU is its ability to
be operated by battery for extended periods of time. Hence it makes
sense to use an 8-bit MCU with a large operation voltage range from
3.6v down to 0.9v. (EM6819, such an 8-bit MCU from EM Microelectronic,
makes it a perfect match for BLE beacon applications.)6
A block diagram of a reference design for a BLE advertising bacon is shown in Figure 1. It includes a BLE controller, MCU and a few external components.
The EM6819 has a built-in high efficiency DC-DC converter, which
allows a BLE beacon to operate from a single 1.5v battery by simply
adding an external Ldcdc inductor. DC-DC provides a 2.5v power supply
for the BLE controller and external sensors. If not required, the DC-DC
circuitry could be easily bypassed to convert the design for operation
from a 3v supply.
The BLE beacon software initializes and configures the BLE controller
using a SPI interface, and also collects data from an internal
temperature sensor and an external ambient light sensor as used in the
reference design (the design's flexibility allows integration of a
variety of external sensors). After BLE advertising is enabled, its
payload is periodically updated with the new sensor's read out.
Overall, the software has a very small footprint with less than 2K of
flash memory used for implementation of BLE related functionality.
The MCU clock runs on a factory calibrated internal oscillator, so only
one 26-MHz crystal is required for the BLE radio. EM9301 can support
standard HCI commands via UART or SPI implementation. The reference
design using a SPI bus allows for it to take advantage of a proprietary
low-power mode of operation. With a 500-ms interval between advertising
events and 0dBm RF output power during transmission, the average power
consumption was measured at 300 ua @ 1.5 v.
The antenna port of the EM9301 has a 200-ohm differential impedance that
allows the direct connection of a folded dipole antenna so no
additional matching circuitry is required. Since for some applications a
folded dipole is not practical due to its physical size (~ 45 mm @ 2.5
GHz), other antenna designs may be used and a proper impedance matching
circuitry will be required.
Both approaches are demonstrated in two reference design implementations as shown in Photo 1.
The "LOW COST" design uses a folded dipole antenna and has a minimum
count of discreet components. The design size is 50mm x 30mm and is
powered by one AAA battery. The "TINY" design is only 15 mm x 25 mm in
size and is optimized for space constraint applications. It is powered
by a coin cell battery and uses a space saving chip antenna with a
discreet balun matching circuitry.
Click on image to enlarge.
Figure 1: One volt advertise-only BLE beacon block diagram
Click on image to enlarge.
Photo 1: "TINY" (left) and "LOW COST" (right) reference designs of 1V BLE Beacons.