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Based on notes provided by Basil - N7NIX and Corky - AF4PM

Mount your UDRC™ on a Raspberry Pi 2, Pi 3, Pi 4 or Pi 400

Note: Raspberry Pi 3 Addendum

ARMv6 Raspberry Pis are not supported. This includes the A/A+, Zero, Pi 1 B/B+, and Compute Module.

Make sure the pins are properly aligned and use the supplied standoffs to support the board above the HDMI port.

Universal Digital Radio Controller
Universal Digital Radio Controller

Install NWDR SD Card Image


NOTE: FLdigi is pre-installed on an NWDR image

Verify that Raspberry Pi OS is seeing the UDRC

aplay –l

If you commented out the internal sound chip, as suggested in the Basic Installation notes, only the UDRC will show, otherwise you will see a reply similar to:

card 0: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
  Subdevices: 8/8
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
  Subdevice #3: subdevice #3
  Subdevice #4: subdevice #4
  Subdevice #5: subdevice #5
  Subdevice #6: subdevice #6
  Subdevice #7: subdevice #7
card 0: ALSA [bcm2835 ALSA], device 1: bcm2835 ALSA [bcm2835 IEC958/HDMI]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: udrc [udrc], device 0: Universal Digital Radio Controller tlv320aic32x4-hifi-0 []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Startup and set levels in fldigi

Station Information

On first run, fldigi will bring up the user setup page.
Fill this page with your station information.

Sound Card Setup

Note: Generally the preference is to not have the UDRC selected as the primary sound card on the pi for the user session so as to avoid transmitting system sounds. With recent versions of the operating system this may be the only option as the on-board sound may have been disabled. if you select the speaker icon in the upper right corner of the display the check mark will be on the default user device. If more than one device shows make sure the check is not on the udrc. If only the udrc appears you can leave it as is since the GPIO control limits the possibility of transmitting unintended sound, but be aware that you may have unintended transmissions.

Within fldigi - Select Configure/Soundcard

Select the Devices tab:
  • Select PortAudio and deselect all others
  • Select udrc: - (hw:0,0) for both Capture and Playback
[For UDRC-II ONLY] If radio is set for 1200 baud you may need to select the Right Channel tab and do the following to get audio.
  • Check the reverse left/right channels checkbox
Save the configuration

Set up PTT

Select the Configure/Rig Control
Select the GPIO tab
For DRAWS Left mini Din 6 connector
* Check the box for BCM 12 (GPIO 26 and Pin 32) box check the =1 (on) box on the same line.
For UDRCII or DRAWS Right mini Din 6 connector
* Check the box for BCM 23 (GPIO 4 and Pin 16) box and check the = 1 (on) box on the same line.
  * Note: to use the 15-pin connector select the options for BCM 12

Note: if using RigCAT or FlRig make sure that the “use cat for PTT” box is not checked on the RigCAT tab.
Save the configuration and close the configuration window
Set the fldigi TX Attenuator to –6.0 (Lower right of fldigi window)
Exit fldigi:

Set output levels

Set up radio
Cable UDRC to radio (6-pin mini din or other)
Radio set to low power
Radio on dummy load for an antenna
Radio set to monitor ALC

Setup levels with alsamixer

Make sure fldigi is not running and set initial UDRC output levels using alsamixer
Press F6 and select the UDRC
Using the arrow keys set
  • PCM to –26.5 db
  • Lo Drive to –6 db
With alsamixer running open another terminal window and start fldigi.
  • Click the “Tune” button in the upper right corner of the window.
  • Radio should switch to transmit mode with little to no output power and no ALC indication.
  • Increase PCM until the ALC starts to indicate (on the IC-7000 this is about 2-3 bars of ALC on the digital display).
Exit the alsamixer and save the settings
Use ESC key to exit alsamixer
sudo alsactl store
Settings for IC-7000
PCM: -22.5 db and LO Drive: -6 db which provides approximately 150 mv output for the UDRC.
At this point deselect the tune button and the system is set for the proper SSB output level.

Basic Installation

The following notes are included for reference only as FLdigi comes pre-installed on the NWDR image

  1. From a terminal command line, verify that the UDRC™ is recognized by typing the command
    aplay -l	
    (that's a lowercase l) and observe that udrc is listed as a card. If you do not see it listed, power down and remount the UDRC™.
  2. To preset the pins and levels on the UDRC™ we provide a script. Execute the following:
    cd ~
    curl -L -s >
    chmod +x
    sudo ~/
  3. Optionally disable the internal sound chip by editing /boot/config.txt and commenting out this line (recommended unless you need it for something else):
  4. Reboot the Pi
    sudo reboot

    If using a Raspberry Pi 3

    Lock the bus frequencies:by editing /boot/config.txt and adding the following line at the bottom:


     Save the file and reboot the Raspberry Pi.

    Configure the audio settings for the UDRC™/UDRC-II

    curl -L -s | sudo sh

    Load libraries and header files to support the Fldigi install

    Load fast light toolkit and headers:
    sudo apt-get install libfltk1.3-dev  
    Load samplerate files and headers:
    sudo apt-get install libsamplerate0-dev
    Load PortAudio library and headers:
    sudo apt-get install portaudio19-dev  
    Load FreeType fonts:
    sudo apt-get install libxft-dev  
    Load libraries for reading and writing sound:
    sudo apt-get install libsndfile1-dev  

    Source Code for Fldigi build

    Download the latest version of fldigi from SourceForge.(tar.gz version, version 4.0.12 at the time of writing, adapt if a newer version is listed)
    Unpack the tar file:
    tar -zxvsf fldigi-4.0.12.tar.gz  

    Build Fldigi

    Change to the fldigi-4.0.12 directory:
    cd fldigi-4.0.12  
    Build the object files and install:
    ./configure --with-portaudio  
    sudo make install 
    sudo ldconfig