■ PHOTO 2. The PIC18F47J53 hardware shown here is
designed to drive an AIR module in stand-alone mode using
battery power, or to control an AIR module under the
influence of a PC’s USB portal.
Anaren. We took care of the AIR hardware build ourselves
with the fabrication, assembly, and integration of the
PIC18F47J53 and AIR PLANE modules. There’s no one else
here to fly this thing but us. So, let’s start flipping software
switches and see if we can’t get this baby on the AIR.
A SOFTWAIR RADIO
As you can see in Photo 5, all of the modular hardware
components are mounted in the 0.1 inch pitch fiberglass
grid of an EDTP plated-through perf board. The short ends
of standard 0.1 inch pitch male headers are soldered on the
component side of the PIC18F47J53 module. The extended
portions of the male headers are long enough to pass
through the perf board and act as wire wrap posts. I chose
to use a female header to socket the AIR PLANE and its
A2500R24A-EM1 evaluation board cargo.
GETTING AIRBORNE
I applied power to the collaboration of modules
assembled in Photo 5 and did not release any magic smoke.
So, we’re ready to put down a firmware foundation that will
allow us to take our AIR module and supporting equipment
down the runway, and ultimately go AIRborne. To those RF
types that wear the pointy witch hats, the AIR module is a
collection of well-placed coils and capacitors that transfers
data by disrupting small portions of the Earth’s magnetic
field. To a hardware type, the AIR module is a tiny building
block that sits on a particular layout of printed circuit board
(PCB) pads. To a programmer, the AIR module is a logical
collection of registers and FIFO (First In First Out) buffers.
All of the RF plumbing has been done for us by the folks at
My very first serious radio was a Knight Kit Ocean
Hopper shortwave radio (
http://nostalgickitscentral.com/
allied/products/ knight_radio.html). I recall the various coils
that could be plugged in for listening in at different
frequencies. The in-band tuning was done mechanically via
a dial that was attached to a large variable capacitor. The
only software involved in tuning the Ocean Hopper were
my — at the time — itty bitty little fingers.
A couple of HC49-packaged microcontroller crystals
would drown the tiny AIR module. Obviously, as far as the
AIR module is concerned, there’s not enough real estate
available for any mechanical RF controls. Thus, the AIR
module is a fly-by-wire device. Registers and the values
contained within them replace the variable capacitors and
frequency selection coils. In the case of the AIR module, all
of its RF and data handling parameters are controlled by the
contents of the 47 registers enumerated in Listing 1.
After staring a hole into the front panel of my Ocean
Hopper, I longed for some visual feedback on the signals I
was receiving in my headphones. Back in the day, the more
sophisticated shortwave receivers came equipped with
signal strength meters. Although a mechanical meter could
be electrically adapted to the AIR module, an external
mechanical or electronic metering device would be overkill
as the AIR module has a built-in set of digital meters in the
guise of status registers. The set of digital status meters are
contained within the register set you see in
Listing 2.
Listing 2 also exposes the AIR module’s PATABLE and
The PATABLE
consists of eight
bytes and is
instrumental in
dialing in the AIR
module’s transmit
output power.
Our PATABLE
setting looks like
this:
■ PHOTO 3. The A2500R24A-EM1 is the
marriage of an A2500R24A AIR module and
a Texas Instruments-inspired daughterboard.
■ PHOTO 4. The AIR PLANE eliminates
the need to permanently mount an AIR
module in the hardware/firmware development
phase of the design cycle.
//*********
//* AIR
//*PATABLE SET
//*FOR 0dBm
//*********
const unsigned
int8 AIR_PA_
TABLE[8]=
{56
August 2011
