Issue #6 - Frequently Asked Questions

We’re going to take a little break from our normal approach of presenting new hardware and software components for the Digital Breadboard, and this time step back to answer many of the good questions that have surfaced from readers over the last five installments of this project. Wow, it really has been over 15 months since the “DigBB” adventure was conceived as project in my regular Digital QRP Homebrewing column of QQ magazine. Much progress has been achieved along the way and we really hope you’ve been keeping up with us here in the column’s companion website.

The Breadboard design evolved along the way with compromises and assumptions being made at various points to help us through technology limitations. These mid-course corrections allowed us to more effectively meet the project goals for packaging, power consumption and functional completeness.

So, all things considered, this installment of the Digital QRP Breadboard project will deal with “Frequently Asked Questions” that have come in from readers over this period of the design evolution. We’ll put them in a logical order and answer them in a comprehensive manner, so you too will be able to better understand just what the Digital QRP Breadboard is and how you can benefit by using it in your shack.

Project Summary

To give everyone a good grounding before we dive into the detailed Q&A format, here’s a brief overview of the Digital QRP Breadboard project as it currently exists in its “Generation 1” first release form.

The Digital QRP Breadboard is a flexible and reprogrammable QRP accessory that can be used in a variety of ways in the shack or out in the field. Housed initially in a handheld enclosure approximately 3.5" x 7.5" x 1.2" in size, this microcontrolled project contains a number of peripherals that most QRPers find useful in applications around the shack – an LCD, shaft encoder, DDS frequency synthesis chip, audio amplifier, RS-232C serial port, general purpose I/O buffers, and a daughterboard expansion port all provide convenient design flexibility. You’re able to download new software from the Internet and reprogram your Digital Breadboard to have it serve as an antenna analyzer, a memory keyer, an audio filter, a keyboard-driven data terminal, a controller for your HF rig, a frequency counter, and more. An inexpensive PSK31 controller is even possible when the DSP daughterboard is used. In addition to a number of low-level software building blocks, the first full-scale application to be made available for the Breadboard is the "Antenna Analyzer II" instrument. You can see its features and capabilities at the Antenna Analalyzer web pages.

Do I need to be a software programmer to build and use the Digital Breadboard?

Not at all! You don’t have to know how to write software programs to use the HC908 in its basic form. Anyone can just download software programs from the DigBB website and load it into the HC908 Daughtercard. The Digital Breadboard then takes on the behavior of this new program, whether it's a voltmeter program, a "commander" rig controller program, or a VFO program. The kit even comes pre-loaded with the first program, the DigBB Monitor Application, so you don’t even have to perform the software download operation until later on.

How extensible is the Digital Breadboard?

The beauty of the Digital Breadboard is in just how flexible and extensible it is. Using its built-in capabilities with a variety of simply loadable software programs available from the DigBB website, it can operate as any of 22 different test & measurement instruments on the bench. And the list keeps growing! Plus, if you find that the Digital Breadboard doesn’t have a specific peripheral device that you happen to need (e.g., a DTMF encoder chip so you can have the DigBB dial a telephone), just add the desired chip in the PCB area reserved for “user expansion”, wire it up to some unused I/O pins on the HC908 card connector, and add a software “driver” routine that to control the chip’s operation. This is truly a digital QRP homebrewer’s dream system.

What’s included in the Digital Breadboard Kit and how much does it cost?

The Breadboard Kit contains a PC board, all board-mounted components (ICs, resistors, caps, etc.), display, shaft encoder, keypad, mini PS2 keyboard, connectors for RF, power and serial port, a potentiometer and a plastic enclosure, as shown in the photos. It also comes with the HC908 Daughtercard, which is fully assembled and tested … all you need to do is plug it into the pinheaders on the base PC board. A manual is also included to assist with kit assembly and use. At the time of this writing, the Breadboard Kit is estimated to be $125, however, it's not quite ready. Check the “ordering” section on this web page (link to be provided when kit is available) to find the current price, as deals are often discovered on bulk-quantity parts and the club passes these savings on to the customers. Further, options are identified to exclude certain components and thus reduce the price. For example, if you do not wish the keyboard option, or if you separately purchased the HC908 Daughtercard, you can reduce the overall price tag on your Digital Breadboard Kit.

What’s the difference between the Digital Breadboard and the Antenna Analyzer?

These two projects use the same hardware platform but just have different software loaded. We started out thinking that a downscaled Breadboard Kit would serve as the antenna analyzer that N2CX and I described at FDIM 2001 and in subsequent magazine articles. But we later determined that nearly each component of the Breadboard would serve us well in the analyzer project too! Thus, the hardware parts plus the dedicated Antenna Analyzer software program constitute the Antenna Analyzer Kit. Similarly, the hardware parts plus the more general purpose software program constitute the Digital Breadboard. This arrangement really is ideal for the owners of the Digital Breadboard Kit, in that all you need to do to turn it into an Antenna Analyzer is download a software program from the website and load it into the unit.

What software comes in the Digital Breadboard Kit?

The software program called “Exerciser” comes preloaded in the HC908 Daughtercard that comes in the Breadboard kit. This is a program that provides simple granular control over the various I/O peripherals in the kit. The Exerciser software contains various subroutines in its library that allow for reading a shaft encoder, setting a DDS frequency (and thus serving as a rudimentary VFO), reading analog voltages, reading/interpreting signals coming from the reflectometer, reading frequency and other such functions. "HCmon" also comes preloaded in the Digital Breadboard. HCmon is a debug monitor, loader and programmer that allows the user to load and debug new software programs onto the platform, overwriting the DigBB Exerciser application software to turn the Breadboard into a different piece of useful gear for the bench.

What are the capabilities of the HC908 Daughtercard?

The HC908 card is a 2” x 2” pluggable daughtercard containing the 8-bit 68HC908AB32 microcontroller on the topside; and the clock, voltage regulator and an RS232 serial port driver on the bottom side. The 68HC908 MCU has 32KB of flash memory, 1 KB of RAM, 512 bytes of EEPROM, 51 general purpose I/O pins, an 8-channel 8-bit A/D converter, two 16-bit timer ports, a programmable interrupt timer, and has a powerful CISC instruction set that can be programmed in assembly language of in C. By pressing the pushbutton on the top, the user instructs the HC908 card to load a new software program from a PC connected to the RS232 serial port. The red LED on the topside turns on to indicate that the HC908 card is awaiting connection to the PC. Once a specific software program is loaded, the power can be removed and the HC908 card retains the program. When power is applied again, it starts running the new program. All of the 51 I/O pins on the microcontroller are available for any custom circuit you might have in mind!

Can the HC908 Daughtercard be used in other projects?

Most assuredly! In fact, this universal applicability is why we chose to make the form factor that of a pluggable daughtercard. Because the HC908 Daughtercard is a self-contained controller it could be very useful as the heart of custom projects well before the overall Breadboard became available. One could take the HC908, apply 12V power and use it as a standalone microcontroller unit for a smart terminal, a computing engine for a weather station, the brains of a security system, and more. It has gobs of I/O lines that can be used to control just about anything imaginable.

Can the HC908 Daughtercard be purchased separately?

Sure. You can buy the HC908 separate from the Digital Breadboard Kit and us it in one of the applications mentioned above.

Does an instruction manual come with the HC908 card and the Digital Breadboard?

You bet. Just as with every kit provided by the NJQRP, both the HC908 Daughtercard and the Digital Breadboard Kit come with a manual describing assembly, theory of operation, test, configuration and usage notes. [Note: The HC908 Daughtercard comes fully assembled and tested.] Additionally, because of the user-reprogrammability nature of these products, there are detailed notes on obtaining and loading new/updated software programs. No special or extra programming cable or board is necessary, as it’s all built into the HC908 boot loader program.

Can the Digital Breadboard be effectively operated on batteries?

Sure. The overall current requirement is about 180 ma at 12V. Should you decide to utilize the internal 10 AA-cell battery holder, field operation is possible over an extended period of time.

How can I start learning about programming on the 68HC908 microcontroller?

The HC908 Daughtercard can indeed be a good platform for actually learning about programming. Using the tools freely available on the Internet, you could modify our existing programs to do some special features that you dream up, or you can develop an entire new program yourself to read the A/D converter, send text to the LCD, or control whatever else you might have wired into your "system". Playing around with the HC908 Daughtercard this way is a great way to bootstrap yourself and learn some of the basics of software programming. Besides reading through the early chapters of the good Motorola manuals for the 68HC908 processor, the best way to study up a little is to browse the many application notes listed on the Motorola website. You can get there from the "Motorola Reference Docs" link in the leftmost column of the NJQRP website links page (www.njqrp.club/links.html). Try entering the software examples they present and see if you can understand what's being attempted by following the liberally commented programs and explanation documents.

What tools are available for developing custom software programs for the HC908 Daughtercard in the Breadboard Kit?

Programming your HC908 Daughtercard can be as simple as editing the well-commented source code files provided with the project by using the free editor/assembler from P&E Micro. Just download the free development suite software from the P&E site by following these five easy steps:
    1) Go to the P&E Micro website (www.pemicro.com)
    2) Select the link called "Motorola M68HC908 Software/Docs "
    3) Select link for "Download the most recent versions of our ICS software packages"
    4) Enter your name and email address
    5) download the HC908ICS08 software package.
Once unzipped and installed, you have a combined editor/assembler/debugger for source code programs. You can then download any source code files you edit and compile to the HC908 Daughtercard via your computer's serial port using the built-in boot loader program.

What’s the difference between the Digital Breadboard and the QuickieLab?

Perhaps the easiest way to describe the QuickieLab is that it’s a “quick ‘n easy” computing platform that has no enclosure, is more expensive, and is lots slower as compared to the Digital Breadboard. Similar operations can be performed on each, but the BASIC Stamp microcontroller used in the QuickieLab is about 1000 times slower than the 68HC908 processor used in the Digital Breadboard. So, although you can output a frequency (for example) from either project, the Digital Breadboard can do much more per unit time, like scan through a range of frequencies, perform complex calculations in a blink of an eye, and be taken to the top of a tower for some antenna measurements in the field. The QuickieLab, on the other hand, is typically going to be desk-bound with rather delicate electronics and wires plugged into its plugboard serving as a test bed for experiments designed by Joe Everhart, N2CX and often outlined in his regular “Joe’s Quickies” column. Perhaps an easier way to compare the two platforms is to consider the table below.