This DAB radio project is based on a Raspberry Pi and the board DAB DAB+ FM Digital Radio Development Board Pro with SlideShow from MonkeyBoard.

This project is still a proof of concept! At the moment the hardware connections are done on a breadboard. You can see the wiring setup in the file wiring_schematics.pdf:

• A Raspberry Pi is used as base unit
• A HifiBerry DAC+ is used as audio output because it offers I²S input pins
• The GPIO connections from Raspberry Pi to HifiBerry DAC+ are done by breadboard wires
• The MonkeyBoard (DAB receiver board) is connected to the Raspberry Pi with an USB cable to control it via a serial port (/dev/ttyACM0)
• The I²S bus lines from the MonkeyBoard are connected to the HifiBerry DAC+ directly. The I²S lines of the Raspberry Pi are disconnected.

This project doesn't work on the native audio outputs (HDMI and 3,5mm socket) of the Raspberry Pi neither on USB soudcards!

The I²S audio output of the MonkeyBoard needs an I²S-DAC like the PCM5122 from Texas Instruments to convert the digital audio data into analogue signals. To make this demo DAB radio work you will need an I²S DAC board like for example the HifiBerry DAC+ where the I²S connectors are disconnected from the Raspberry Pi and connected to the MonkeyBoard instead as shown in file wiring_schematics.pdf.

Download the latest Raspbian Stretch with desktop and recommended software ("full image") and flash it on a SD card with capacity of 8GB or higher as described by the Raspberry Pi Foundation here.

Modify the file /boot/config.txt for activating the HifiBerry DAC+ or a compatible board:

sudo nano /boot/config.txt

and change the audio driver overlay like this:

# Disable audio (loads snd_bcm2835)
#dtparam=audio=on
# Enable the I2S DAC:
dtoverlay=hifiberry-dacplus

Reboot the Raspberry Pi and start a fake audio playback of a freely chosen audio file via I²S:

omxplayer -o alsa /home/pi/Music/any_audiofile.flac # alternatively any *.mp3 file

Of course, you won't hear anything from this audio file because the I²S wires were disconnected from the Raspberry Pi. But the I²C connection of the DAC (PCM5122 resp. HifiBerry DAC+) continues to be necessary for setting the I²S DAC into an active playback mode which will be used by the MonkeyBoard later.

Clone this repository onto the Raspberry Pi and start the installation shell script setup.sh in an LXTerminal:

cd /home/pi
git clone https://github.com/schlizbaeda/DABradio
cd DABradio
./setup.sh

Now the KeyStone library delivered by MonkeyBoard is installed properly on the Raspbian OS for further use.

dabd is a DAB radio daemon which accepts commands from stdin and sends its result strings to stdout. So you can control dabd using the keyboard.

Call the software dabd in the LXTerminal:

cd /home/pi/DABradio
./dabd

Start audio playback by entering the following commands into the LXTerminal. They will be read by dabd:

open
set volume 9
set stereo 1
scan
list
playstream 14
close
quit

As you can hear, the DAB playback continues after the connection to the MonkeyBoard was closed and the application itself has quit. At my home the parameter 14 of the command playstream ... represents Radio BOB!, my favourite DAB+ station. Enjoy listening to DAB Radio.

Using the named pipe (FIFO) mechanism of Linux offers a lot of possibilities to redirect the DAB radio control to more convenient user frontends as there are

• Graphical User Interface
• GPIO control (e.g. hardware push buttons or even a remote control via LIRC)
• Web server control via browser

This Python3 script offers a simple tkinter GUI to control dabd. Call this script standalone in the LXTerminal:

./dabgui.py

Test this GUI application by entering some keyboard text. Each line entered in stdin of the LXTerminal will be printed into a textbox of the GUI. Any command sent by clicking onto the buttons of dabgui.py will be sent to stdout. So it will appear in the LXTerminal window.

On Linux anonymous pipes are created by shell commands like

ls -l | grep less

The disadvantage is they offer only a data transfer in a single direction. But to use an interactive frontend for dabd a bidirectional mechanism is necessary.

Linux Named Pipes are special files which can be read or written by shell redirection. Detailed explanations can be found at www.linuxjournal.com/article/2156 or at unix.stackexchange.com.

You need two named pipes, one which sends commands from the GUI to dabd and another one which receives the data from dabd. Their names are chosen as fromDABDand toDABD and they were created by the installation script setup.sh with command

mkfifo fromDABD toDABD

The shell script dabradio.sh calls both programs using the Named Pipes in this way:

./dabd >fromDABD <toDABD &
./dabgui.py <fromDABD >toDABD

First this application starts another thread to read its commands from stdin in parallel. Then it creates the class KeyStone which contains several methods to control the DAB radio board.

To convert the UTF-16 strings returned by the original KeyStoneCOMM.h into UTF-8 strings the GNU library libiconv is used.

Typing the command help on stdin inside dabd prints a short help text onto stdout.

The MOT slideshow feature isn't implemented yet because there are some issues. It doesn't work properly!