BreadBoard
Project
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PROJECT
DESCRIPTION
The
Digital QRP BreadBoard is a general-purpose QRP accessory that can be used on
the operating bench and in the radio shack in a variety of ways.
Approximately 6" x 9" x 1.5" in size, this project contains a number of peripherals that QRPers find
useful in applications around the shack – an LCD, shaft encoder, DDS chip,
audio amplifier, RS-232C serial port, general purpose I/O buffers, and a
daughterboard expansion port all provide convenient design flexibility.
You'll
be able to download new software from this website and reprogram your Digital BreadBoard, allowing it to serve as a memory keyer, an
audio filter, a keyboard-driven data terminal, a controller for your HF rig, a
frequency counter, and more. Sharp readers will glean that we'll even be
able to make an inexpensive portable PSK31 controller with the DSP daughterboard
to be introduced in a near-future installment of the Digital BreadBoard project.
The
Microcontroller
We selected the popular and inexpensive Motorola
68HC908AB32 microcontroller as the heart of the BreadBoard project. It
was necessary to select such a CISC (complex instruction set
controller), instead of a low-end RISC (reduced instruction set
controller) like those in the Microchip PIC family. The software already
being designed to control the vast array of peripheral chips and I/O
functions would be present great programming challenges in a RISC device
because of inherent program memory and register memory addressing
restrictions. The 'HC908 is the Motorola equivalent of the popular
8051-class of processors from Intel, SST, and others offering plentiful
I/O capabilities, unrestricted addressing and high clock speeds.
Programming Considerations
One of the prime goals for this project was to have the BreadBoard be
easily and inexpensively reprogrammable, even after built and used
long-term by the homebrewer. Of course the unit has ample onboard FLASH
memory, simplifying the board design and making for a non-volatile
project. That is, the microcontroller retains its program memory
even when power is removed.
But getting the software program into the device is often a concern for
microcontroller homebrew enthusiasts due to the expense of the
"programmer". Oftentimes it's necessary to purchase a
$100-or-more programming board from the manufacturer that will allow you
to burn your custom software into the controller's flash memory. In
many cases one is able to homebrew this programmer (as in the case of the
PIC devices), however this is yet another project that must be done before getting to the fun part of experimenting with your intended
project.
Our 68HC908AB32 device has the ability to be in-circuit programmed,
which means that a conventional +5V power supply and proper timing is all
that's required in order to burn a new program into its flash memory ...
even while on the target pcb of your project! We've developed a
special boot loader program that allows you to download the binary image
of your program over the built-in RS232 serial data port connected to your
PC. All you need to do is develop a program with the (free) software
development tools on your PC, download it to the BreadBoard and bingo,
you'll be running your new and improved program. In this way you'll
be able to take advantage of newer software programs that we'll be
providing for download on this website, or you can develop your own
customized versions of the programs. Pretty cool, eh?
I/O, I/O, it's off to work we go
Another big factor that played in the selection of the Motorola
68HC908AB32 microcontroller was its massive number of I/O ports. We
need lots of I/O (input/output) bits in order to control all the devices
planned for this BreadBoard ... the LCD, DDS, pushbuttons, 7-segment LEDs,
keyboard, keypad, et al. Using all these devices takes lots of bits,
and this 'HC908 device has lots! Take a look at the online
datasheets for the 'HC908AB32 for now and we'll be presenting the
schematic in the next installment of the column.
First Things First
The first of the BreadBoard's capabilities to come alive will be the
'HC908 controller daughtercard itself, a 4x16 character LCD, a serial
keyboard input device, and an analog input port to measure SWR or RF power
indicating voltages. Besides being able to see the project start to work
by seeing characters on the LCD display as typed on a standard PC
keyboard, you'll actually be able to use the project as a crude
measurement device. Description, construction information, source
code and a beginner's kit (pcb, parts, manual) are now being prepared and
will be offered in the next issue of our column.
Evolving Design
There's so much more to describe about the design, layout and construction
of this project. We'll be getting into more of it very soon with the
next column, and even sooner on this webpage. So please
revisit these web pages often and you'll be sure to stay well
in tune with the evolving design of the Digital QRP BreadBoard.
Page last modified:
November 28, 2001
Copyright 2001 G. Heron, N2APB
n2apb@amsat.org
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