With the release of the Icom 7300 a few months ago, a built in spectrum / waterfall display has become a very popular idea. The little Elad FDM-DUO when connected to a computer and the FDM-SW2 software clearly trumps the IC-7300 when it comes to the powerful features of PC driven SDR. However, sometimes something simpler might be better at times. This has been the charm of the “no computer needed” Icom 7300.  The Elad FDM-DUO is also a standalone knob and button controlled SDR, but you lose the additional functionality of the Spectrum / Waterfall when operating standalone. Thanks to the hard work of Giavanni HB9EIK in cooperation with Elad you can now add a wireless bluetooth remote control scope to the FDM-Duo using an Android tablet or phone. The remote will allow for touch tuning of the Elad FDM-DUO via the the spectrum /waterfall display as well as change bands, toggle the PTT and Tuning features, and turn on and off various setting like noise Noise Blanker, Noise Reduction, etc. All with no PC required. Since the scope / remote is wireless, it can be placed in a more convenient location or operating position to allow for easier access to the FDM-DUO’s controls. Right now, there is no audio is passed to the Android device so basically the Android device becomes a remote display and controller for the FDM-DUO. This is all made possible with Giavanni’s BLUEDUO Android software and by adding an external bluetooth serial interface to the FDM-Duo’s 9 pin interface jack located on the back of the radio. Now to be fair the BLUEDUO Android software is more of a “beta” stage than a complete project. Even though the BLUEDUO software is working very well at this point there may be frequent updates to add new features.

The bluetooth connection is provided via an HC-o5 serial bluetooth module. The HC-05 allows a two way wireless bluetooth connection to be made from the FDM-DUO’s external interface port to the BLUEDUO application running on the Android device. The software has been tested on Android devices running the Kit Kat and Lollipop versions of Android and seems to work fine.

There has been some mention that Elad may produce a preassembled version of this blue tooth interface in the future. However for now, you will have to build your own interface. This requires changing some settings on the HC-05 module via a  Raspberry PI and connecting four wires to a male DB9 serial connector. Actually it’s pretty simple to set up once you know what you are supposed to do. The cost of the project can be very inexpensive (about $10 to $15) depending on what you have on hand. Probably the most intimating part of the project is programming the HC-05 bluetooth module since the module generally comes with no documentation. The Raspberry PI  was chosen as the programming device since it provided all the necessary connections needed for the HC-05 chip. To make this project as easy as possible we put together a step by step video showing how to wire and program the HC-05 module and wire it to the male DB9 connector. One important thing to do if you decide to try this, is make sure that all the FDM-DUO’s firmware is up to date! Below you will find a resource list of the parts and wiring diagrams necessary to complete the project. Have fun!

Parts List: (continued on page 2)

6 thoughts on “Wireless Touch Screen Remote for the Elad FDM-DUO”
  1. With the new Raspberry PI 3, the things changed a bit.

    1) Raspberry PI 3 uses ttyAMA0 for Bluetooth, so you have to use /dev/Serial0
    2) The serial line must be enabled in /boot/config.txt using the line
    3) due to the limitation of the UART used, that relies on CPU clock, in /boot/config.txt the cpu speed has to be fixed using the line
    4) In the graphical configuration (Menu “Settings” – “Raspberry PI configuration”) in the “Interfaces” tab (or in the terminal with sudo raspi-config), the “Serial” interface may be enabled (or not), this does apparently not harm.
    5) To avoid the occupation of the serial line by a console you have to verify in /boot/cmdline.txt that the parameter console has no reference to things like serial o dev but only to tty1 or similar
    6) In case of an already present errno 11, it could be of help to try to stop login consoles on /dev/ttyS0 using the command
    sudo systemctl stop serial.getty@ttyS0.service

    (With the most useful help of Giovanni, HB9EIK).

  2. Weird problem have the BLUEDUO APP paired fine with HC-05 module now BLUEDUO , I can change bands, modes NB NR , have both Spectrum and Waterfall but no Frequency or S-meter readouts, Also not sure if the line of Vol Mod BW under the Freq. is supposed to change.
    Running a Samsung Galaxy Tab S with Lolloipop.

    Any ideas greatly appreciated , Still usable but not complete.


  3. I successfully programmed two HC-05’s using your excellent instructions! Thank you! However a second set of chips starts in the Program Mode (slow flashing red LED with no blue LED visible) I can proceed with programming (Using Pi and Cutecom) but device is recognized… Shouldn’t these chips start in the Operate Mode? Thoughts?

  4. unfortunately, this is not working for me. I’ve followed step by step the instructions (also the ones for Pi3) and I can’t still have a connection on serial0… any ideas?

    1. Vitor,
      I had to do some juggling to get the hardware UART connected to the GPIO pins. Here is a link to a process to do exactly that. Worked for me the first time.


      The “virgin” HC-05 came up at 34800 baud in my case. I started with the baud rate at 9600 and worked my way up. One caution, close the device change the baud then open the device again with Cutecom. Also, try the version command a couple of time, if the wrong baudrate makes an error it takes a few characters to get it cleared out.

      Bob – N4RFC

Leave a Reply

Your email address will not be published. Required fields are marked *