DESIGNCYCLETHE
ADVANCED TECHNIQUES FOR DESIGN ENGINEERS
■ BY FRED EADY
FLASHFLY SYSTEM GETS
STAMP OF APPROVAL
Never underestimate the power of a BASIC Stamp. The first Stamp I ever saw
was in charge of a small CNC machine’s main stepper motor, among other
things. When it comes to proof of concept, the Stamp excels. I’ve personally
seen Stamps used in the initial production of scientific instruments that
supported ground and flight hardware used in the spaceflight program.
The BASIC Stamp appeals to both machinist and scientist because it
is easy to use. The Stamp is yet
another proof that can be applied to
Fred Eady’s First Rule of Embedded
Computing. The Stamp is easy to use
because all of the embedded firmware
and hardware work has already been
done for you. Thus, as my first
embedded computing rule states,
“Nothing is free.” However, in the case
of the Stamp, you didn’t have to pay.
In this month’s Design Cycle, we
are going to expand the power of a
BASIC Stamp 2 using a pair of XBee
radios and an extremely clever RF
system. The XBee radios are the heart of
a system that enables a Stamp-based
computing platform to operate
beyond the wires. This wireless layer of
a Stamp application is called FlashFly.
FLASHFLY 101
Regardless of the FlashFly system
configuration, the base module and
remote module both require the
presence of an XBee radio module
like the one under the lens in Photo 1.
When the FlashFly USB Stamp adapter
is acting as the remote application
module, the XBee radio module is
physically carried by the adapter.
THE FLASHFLY
BASE MODULE
Photo 2 is a fly’s eye view of a
FlashFly base module in its out-of-the-box preassembled form. If you take a
moment to closely examine the
hardware in Photo 2, you’ll see that
an FTDI FT232RL USB-to-UART bridge
IC is the personal computer-to-XBee
radio interface.
The XBee radio module you see
in Photo 1 is accommodated by the
pair of 2 mm female headers that will
be soldered into the base module’s J1
and J2 header positions. The FT232RL
USB-to-UART IC is configured to drive
its I/O subsystem at 3. 3 volt logic
levels which are compatible with the XBee radio module’s
3. 3 volt I/O engine. Power for the base module electronics
is derived from the USB portal’s + 5.0 VDC power supply.
The USB-to-UART IC performs the 5.0 VDC-to- 3. 3 VDC
power conversion internally while the XBee radio module
receives its + 3. 3 VDC power via the output of a Microchip
TC1262-3.3 LDO voltage regulator. Since everything
■ PHOTO 1. The FlashFly XBee radio
modules operate in peer-to-peer mode
under the rules of 802.15.4. This
particular XBee radio module has a
maximum range of 100 feet indoors
and 300 feet outdoors.
52 July 2011
A typical FlashFly system consists
of a BASIC Stamp module, a FlashFly
base module, and a FlashFly remote
module. If the FlashFly remote module
is not in the form of a FlashFly USB
Stamp adapter module, a FlashFly RS-232 adapter board
may be part of the FlashFly system.
FlashFly modules can be had as factory assembled
units or semi-kits. In my opinion, the only way to become
and remain a good soldering technician is to practice. So,
all of the FlashFly units used in this discussion arrived on
the Design Cycle bench in kit form.
