DXDUSB – A USB-only Interface for the DX Doubler

***** 6/31/2017 UPDATE in the Status Section below *****

Installation Instructions Will be posted here soon DXDUSB Install 7_1_2017


The DX Doubler is a great SO2R and general Ham Station controller, if you have more than one radio. This page is about the development of a USB-only interface to take the place of the aging Parallel Port (LPT) that is native to the DX Doubler box. I periodically post some updates on the KG3V.com Blog, but this page provides one place to get all necessary information for using the DXDUSB in a Station.

There are two reasons that I started this project; 1- I wanted to use my DX Doubler with any computer and parallel ports are becoming scarce, and 2- it looked like a great excuse to use a small Arduino computer board (the Arduino Pro Mini) and build a custom PC board. This Page tells you all about the project and provides some instructions for setting up (not much work) and using the DXDUSB interface.

I know there is a product out there that allows use of the DX Doubler with a USB interface. That product has been around for quite a while, is fairly expensive, and very complicated to setup and operate. It does provide a more general-purpose USB –> LPT converter. The DXDUSB is intended specifically to make a USB interface that uses existing Contesting/Logging  software – no special is software required. The only thing you need to Load is the standard driver for an FTDI chip. In more recent versions of WINDOWS, you may not even need to do that.

What Exactly is the DXDUSB?

DXDUSB is an interface that captures and decodes Serial commands generated by the Open Two-Radio Switching Protocol (OTRSP). This Protocol was created by Paul Young K1XM specifically for interfacing Contesting software with SO2R Hardware.  While OTRSP was initially developed and used with some other hardware, Paul was generous enough to make this protocol available for all to use. This resulted in several popular Logger Applications including it as an option for interfacing with external devices. Software such as N1MM+ now can be configured to use this protocol.

The DXDUSB simply receives a serial character stream in the OTRSP format (which N1MM+ generates), decodes the data, then configures a set of digital input/output lines to mimic the pins of the LPT port that connects directly to the DX Doubler box.

The DXDUSB employs a custom PC Board containing all the parts needed for this interface. the major components on-board are an RJ-45 (Ethernet-like) connector for the OTRSP interface and an Arduino Pro Mini to handle the command processing. There is also power conditioning and support for using a USB connector or 12 Volt interface for Power. While this board was developed specifically for Using a USB Port to control an SO2R box, it may be useful for other Applications where you want a number of I/O lines brought out from a Pro Mini Board and a simple serial interface to talk to it.

What Software and Hardware can be Used with the DXDUSB?

The DXDUSB was developed primarily for use at my Station where I use N1MM+ contest Logging software and the DX Doubler SO2R interface hardware. I have made every effort to develop the software to support other programs that also have parallel port SO2R options, but I have not yet done any compatibility testing.

What is the Status of DXDUSB Development?

In December 2016, a custom PC Board was developed for the DXDUSB. That board is now in its third iteration. Various versions of the DXDUSB have been in testing (including heavy Contest use) for about  a year. The DXDUSB allows powering by either 5 VDC (USB connector) or 12 VDC (although I recommend the 5 volt interface). It also provides all the interface lines that appear at the LPT connector of the DX Doubler, including the Band Data. Using a single USB –> Serial interface, it also provides outputs for CW Keying and PTT control.

The DXDUSB supports only one model of a USB –> Serial interface cable. This may not be a popular decision, but there are a couple reasons. Many people struggle with compatibility issues when trying to use various USB –> Serial solutions (at least with N1MM). It is well-know that some of the interfaces are problematic, especially those using the PROLIFIC chip set. . The interface I use is a CISCO-compatible cable that incorporates an authentic FTDI chip. It also has an RJ-45 connector that makes interfacing easy.

1/2/2017 Update – I built a couple prototypes with the latest custom PC board. Electrically they work fine, but there are some mechanical issues with alignment of the board and the chassis I am using. This will necessitate one more spin of the PC layout. Hopefully that will be the last and I can get some built-in a final format.

**** 4/2/17 UPDATE **** – I finally appear to have solved one last annoying software bug. It was causing the DXDUSB code to stop running on a very infrequent basis. This NEVER happened during actual use of the DXDUSB, it seemed to happen when it was not in use for several days or weeks. It now appears that this is a solid hardware and software platform. I still have to do one more run of the PC boards to improve the mechanical layout, so it fits nicely inside a small chassis.


***** 6_31_2017 UPDATE ***** The DXDUSB hardware and software designs now seems to be solid. I confirmed that the bug that caused the infrequent “crashes” (only seen when computer was powered-off) have been eliminated. Software Version 1.2 fixes that annoying bug. I am making some of the current generation units available to people that can live with the “prototype” nature of the current package. These are built to-order, and may take 2-3 weeks for delivery. Interested parties can contact me via email at mycallsign@chesbayva.com (substitute KG3V for mycallsign).