Basics of Bluetooth Technology
By Stephen Bucaro
Bluetooth is a wireless technology for short range communication. It's application ranges
from wireless computer mouse, keyboard, headset, and printer, to home security and wearable
health and sports monitoring devices. It uses the Uses 2.4 GHz (2400 – 2483.5 MHz) ISM
(Industrial, Scientific and Medical) spread spectrum radio band.
The ISM radio band is used by microwave ovens, cordless phones, garage door openers, and
other common devices, so it can be noisy. Bluetooth provides functionality to detect nearby
Bluetooth devices, and in order to mitigate interference, implements frequency hopping.
To detect nearby Bluetooth devices a master device Sends out an inquire, which is a request
for nearby devices (within 10 meters) to issue a response that allows them to be discoverable.
A master device can also work in slave mode and issue a response that allows them to accept
connection to another master device. A slave device can not initiate a connection, only
accept connections. Note that nearby devices where the signal is blocked by something like
a metal file cabinet can be undiscoverable.
Up to 8 Bluetooth devices can be connected in master/slave configuration called a Piconet
There can be up to 7 active slaves for each master. A three bit address (AM_ADDR) is given
to each active slave. Piconets can be combined to form scatternets providing unlimited
• To be found by other Bluetooth devices, the first device must be set to
discoverable mode, this allows other Bluetooth devices within the discoverable distance to
detect its inquire and issue a response in attempt to establish a connection.
• When two devices find each other they detect what type of device they are,
cellphone, headset, etc., along with its Bluetooth device name. The Bluetooth device name is
assigned by the manufacturer, or it can be assigned by the user.
• The two devices agree on a code they will use for passkeys and the master device sends a passkey.
• The slave device sends the passkey and the passkeys are compared and if they are both
the same, a trusted pair is formed and a Bluetooth connection is established.
• Once the Bluetooth pairing has occurred, communication can be exchanged between the devices.