DDS VFO using the DDS-30 or DDS60 daughtercard and
| Description | Block Diagram | Features | Instructional Videos | Schematic | Parts List | Modules | Documentation | Software | Ordering |
Views of the prototype HC908 VFO module mounted in an optional Ten-Tec enclosure. (Click on a photo to see a larger view.)
The HC908 VFO project has taken a dramatic step forward in being a full-blown and capable VFO product, suitable for use as test equipment, an add-on digital dial to boat anchors and QRP transceivers alike. The software has been substantially expanded and improved to make it a unique and low cost offering in the ham markets, yet still possessing features and performance to rival any other. This is due to the flexible and extensible nature of the core design's use of the HC908 controller card and the popular DDS-60 signal generator card. We are in the process of completing a single pc board that will hold both of these daughtercards, the LCD and the rotary encoder. At that point, expected during April, we will offer the product for sale as a kit of pcb, modules and components. It also will be available as a completely assembled and tested module. Lastly, we'll offer an attractive pre-cut enclosure option to house your HC908 VFO with enough room to contain other radio circuits and components.
Mar 9, 2010: Bug fixed for 4x scaling (i.e., freq multiplier). Also removed lower dial limit of 400 kHz (i.e., goes to zero now). Latest version posted: v3c
The HC908 VFO is a full-featured VFO capable of high-quality sinusoid signal generation up to 60 MHz, with features making it uniquely capable within Amateur Radio markets: a high-contrast back-lighted display, a single encoder control, multiple memories, flexible IF offset and multiplier settings to accommodate a wide number of radio design architectures, modular controller (HC908 Daughtercard) and signal generator (DDS-60 Daughtercard), 40 bits of available digital and analog I/O for custom use, an advanced menu system for easy access to all features, and a built-in serial port providing field upgradeability by allowing the owner to download and update the VFO with improved software versions when available. The HC908 VFO is available as a single printed circuit board that may be used with an optionally-purchased standard enclosure or in a custom project chassis. The software source code is freely available for developers to modify and extend VFO capabilities using a free and powerful development suite from P&E Micro.
Continuously-adjustable VFO from 400 kHz to 60 MHz
Displays frequency digits: two for megahertz, three for kilohertz, hundreds and tens. (Display of single Hertz digit in next release.)
Flexible cursor movement to digit desired for changing via Dial
Four easily set and programmable memory buffers available
IF Offset buffer provided to add to or subtract from the active frequency buffer;
1x (direct), 2x or 4x frequency multiplier allows scaled use with SoftRock and other over-clocking architectures
Currently displayed frequency stored in EEPROM after 20-second dial press, and displayed at next power-up.
Backlight timeout logic for auto power saving
17 preset frequency bands may be selected via menus to conveniently establish desired dial frequency, Start frequency and End frequency for subsequent frequency Sweep operation
Additional Custom Band may be programmed to establish user-defined Start frequency, End frequency and Step Size for subsequent frequency Sweep operation
Frequency Sweep function automatically and repeatedly sweeps the frequency generated by the VFO from the Start frequency, to the End frequency, in increments of Step Size. (e.g., useful as input to a filter for automated frequency response measurements.)
High-precision, low power DDS signal generation by the DDS-60 daughtercard (default) for operation up to 60 MHz, or the DDS-30 (menu-selectable) for operation up to 30 MHz
VFO may be calibrated against known 10 MHz reference (or WWV);
Powerful 8-bit microcontroller controls all aspects of the operation
Automatic scanning results displayed as frequencies with lowest SWR
Configurable frequency scanning limits and step sizes
Serial port connects to PC for field-upgradeable software
Features in development: frequency display to units Hertz digit, dual VFOs, A/B split operation, IF-VFO, Rx and Tx frequency scaling, increased frequency memory buffers, remote control and data collection via serial port;
Source code freely available and downloadable from website.
SDK available describing software architecture and development guidelines per the P&E Micro WinIDE development environment (also freely available).
We created a dozen 5-minute video segments that collectively overviews most of the VFO's features, as well as the hardware design and the software development environment (described more completely in the SDK that comes with the product.)
Just click on the images below to be taken to an online "Flip Share" site where you can view the videos individually, as desired. Use the title of each video segment as a guide to what you'd like to view.
The HC908 VFO software can be downloaded to your PC and easily placed into the flash memory on the HC908 daughtercard without using any expensive hardware. Just follow the easy steps to load the S19 binary file into your system and you'll be off and running in no time. The source code is also provided for those wishing to experiment in software.
Source Code (version 3c)
S19 Binary (version 3c)
We are currently creating a pc board to contain the HC908 Daughtercard (currently available) and the DDS-60 Daughtercard (currently available), thus creating a compact and powerful module for hams to use as a standalone digital dial for their rigs, or as a building block for their custom designs.
In early April, we expect to start taking orders for kits, for assembled & tested VFO modules, and for VFO modules enclosed in one of several attractive cabinets.
Please let us know of you are interested in staying informed of progress and pricing as it becomes established, and we'll put you on a private mail list for this information. Contact us at for this.
Lastly, if you just cannot wait for the production units to become available, you may order right now a custom-crafted version of this design, constructed by the designer in the form of the prototype shown at the top of the page. Contact us at for pricing and enclosures, if that option is desired.
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Page last updated: March 9, 2010