42 June 2015
As you may know, Bluetooth is a standard for the short-range wireless interconnection used in cell phones, computers, and other electronic devices. According to Wikipedia, “It was originally conceived as a wireless alternative to RS-232
data cables.” Of course, today, Bluetooth is used for many purposes,
• Hands-free control and use of cell phones.
• Streaming of music for the home, in cars, and even for wireless
• Streaming of data for file transfers between phones and PCs, and
PC to PC.
• For wireless keyboards, mice, and printers.
• For wireless tethering, where “tethering” is the act of sharing a
device’s network connection with another device. Most tethering
is done via Wi-Fi, but it can also be done with Bluetooth. An
advantage of Bluetooth tethering is that it requires much less
power than the equivalent Wi-Fi connection.
• And yes, streaming of serial data as an alternative to RS-232
It is this last purpose that we will be experimenting with in this article.
Abbreviated Bluetooth History
In the early 1990s, a group of engineers at the Swedish company,
Ericsson developed the technology that would later be called
Bluetooth. The name came from a Danish king who in English is
called Harold Bluetooth. Harold united warring factions in his
kingdom, just as Bluetooth technology united technology
companies in their pursuit of a short-range data communication
standard. No one company owns the Bluetooth technology. A
Special Interest Group (SIG) of technology companies work
together to maintain, extend, and promote Bluetooth. As
mentioned, the original intent of Bluetooth was for the
replacement of RS-232 cables, but we all know Bluetooth is much
more than this.
The original Bluetooth technology is today referred to as
classic Bluetooth because of the arrival in 2011 of Bluetooth LE, or
Bluetooth Low Energy (BLE). BLE shares many of the same
attributes of classic Bluetooth, but is targeted for the type of
applications that require extreme low energy usage. In fact, energy
so low that a coin battery like a CR-2032 could power a BLE
device for five to 10 years.
Classic Bluetooth was designed to continuously stream data,
whereas BLE was designed for periodic or episodic data transfer as
would be required for remotely located sensors, for example.
FIGURE 1. The HC-05
serial Bluetooth module.
In a previous article
("Driving LEDs with
April 2015 issue), I
developed microcontroller-based hardware and
software to control a
matrix of 8x8 RGB LEDs. I
thought since I still had
that hardware laying
around, I would use it as a
test bed for experimenting
with Bluetooth. I had never
done anything with
Bluetooth before, so I
thought it was about time
By Craig A. Lindley