Useful Java ME 8 Embedded code snippets

Collection of ME 8 Embedded code snippets:

  • Using java.util.TimerTask and Timer – for scheduling periodic tasks (reading a sensor, checking a status etc eg
MyTimerTask myTimerTask = new MyTimerTask();
Timer timer = new Timer();
timer.schedule(myTimerTask, millisBeforeStarting, millisBetweenExecution);
  • Opening a GPIO pin: =;; // true = on, false = off
  • Adding an EventListener to a switch:
GPIOPinConfig config = new GPIOPinConfig(this.portId, this.pinId,
    GPIOPinConfig.DIR_INPUT_ONLY, PeripheralConfig.DEFAULT,

… where this implements PinListener and valueChanged() method:

public void valueChanged(PinEvent event) {
    GPIOPin eventPin = event.getPeripheral();
  • Opening an I2C device for input/output:
I2CDeviceConfig config = new I2CDeviceConfig(i2cBus, address, addressSizeBits, serialClock);
myDevice =;
  • Read from a UART device:
this.uart =;

InputStream is = Channels.newInputStream(uart);
this.serialBufferedReader = new BufferedReader(new InputStreamReader(is));
  • Read using Generic Connection Framework:
CommConnection conn = (CommConnection)"comm:/dev/ttyAMA0;baudrate=9600");
InputStream inputStream = conn.openInputStream();
this.serialBufferedReader = new BufferedReader(new
  • Open and write to a record store: = RecordStore.openRecordStore(storeName, true);
byte[] dataBytes = data.getBytes();
recordNum = store.addRecord(dataBytes, 0, dataBytes.length);

Running headless WSPR on the Raspberry Pi

I’ve tried a few times to compile and run WSJT on the Pi in order to decode JT65 mode transmissions – I think I got close, but I ran into other issues with the soundcard configuration that has tripped me up, like configuring WSJT to listen and transmit to my soundcard’s inputs and outputs.

I’ve seen some other posts on getting WSPR running, so this looks like it’s more possible.

From going through the WSJT dependencies, I’d already installed all the libportaudio and python-* dependencies. If you’re following this from scratch through, I’d start with George Smart’s article here. To get a working config I followed George’s article first and then picked up LX3KR’s article here to get the soundcard config working – I also wanted to run WSPR in headless mode, so I picked up the steps at this point:

cp WsprMod/ WsprModNoGui/

I’m not sure the suggestion for the .asoundrc file worked for me, as referencing the input as 2#audio and output as 3#radioconv in the WSPR.INI didn’t work.

At this point I did some guessing. When wspr starts up, it writes a list of audio devices to audio_caps file in your wspr dir. Here’s what mine looks like with my Rigblaster Advantage attached:

pi@raspberrypi ~/amateur_radio/wspr $ cat audio_caps
0    1    2       0       0  RIGblaster Advantage Audio: USB Audio (hw:0,0)
1  128  128       0       0  sysdefault
2    0    2       1       0  front
3    0    2       1       0  surround40
4    0    2       1       0  iec958
5    1    2       0       0  spdif
6  128  128       0       0  default
7    0    2       1       0  dmix

So I’m guessing the Rigblaster is device 0 and sysdefault is 1.

From the suggested config in WSPR.INI, it configures the in and out like this:

AudioIn 2#radio
AudioOut 3#radioconv

2 and 3 don’t seem to match up with anything I’m seeing, but since the other earlier step changed the USB sound card devices to be default, I set these instead:

AudioIn 1
AudioOut 1

Before starting up wspr I also ran alsamixer and set the vol and mic levels to be roughly 3/4 volume.
Now when starting up it looks like wspr sees my devices and off it goes:

pi@raspberrypi ~/amateur_radio/wspr $ python 
WSPR Version 3.00_r2326, by K1JT
Run date:   Thu Apr 17 05:14:05 2014 UTC
setting g.Win32
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.rear
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.center_lfe
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.side
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.hdmi
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.hdmi
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.modem
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline
ALSA lib pcm.c:2217:(snd_pcm_open_noupdate) Unknown PCM cards.pcm.phoneline
ALSA lib pcm_dmix.c:957:(snd_pcm_dmix_open) The dmix plugin supports only playback stream
Audio config ok
2014 Apr 17
Rx Noise: -30  dB

The last few lines repeat for a minute or so then it starts reporting the actual volume level. You want to adjust the radio volume or volume on the Rigblaster so that the level is close to 0db. +/- a few doesn’t seem to make much difference.

The other values I changed are:

PctTx 0

This is percent tx time. Leave it at 0 for rx only, otherwise change to a %age of time value that you want to send your own transmissions. I changed it to 5.

iband 2

This represents the band you’re listening to, counted from the list of freq values. 600m is 1, 160m is 2 and so on.

Start it up and off you go!


tmux useful commands

tmux is a great alternative to screen if you’re looking for multiple virtual sessions in one terminal window.

Useful commands:

Ctrl-b c : open new session

Ctrl-b n | p : cycle next / previous through sessions

Ctrl-b % | ” : split horizontally / vertically

Ctrl-b left | right | up |down : cycle back /forward through visible split windows (left/right if split horizontally, up/down if split vertically)

Using Putty SSH, if you’re not getting line characters for the splits, change session charset to UTF8.

Reading from the Adafruit GPS sensor on the Pi

Per instructions in the Oracle Embedded Java MOOC this week, here’s the steps to get gpsd setup to read from the sensor if it’s attached via a USB TTL cable:

sudo apt-get install gpsd gpsd-clients python-gps

ls /dev/ttyUSB* – to check what USB port we’re connected to

sudo gpsd /dev/ttyUSBx -F /var/run/gpsd.sock to start the daemon, replace x with the port number from step above

cgps -s – to run the client


If the GPS is attached via GPIO pins, then, similarly to above:

ls /dev/ttyAMA* – to check what AMA port we’re connected to

sudo gpsd /dev/ttyAMAx -F /var/run/gpsd.sock to start the daemon

Check check you’re reading data from the connected port, you can do:

cat /dev/ttyAMA0 – and you should see the raw messages being read from the card.

To interpret data coming from the card, read a line until you get a line prefixed with $, and then the next 5 chars represent the message type:

$GPGGA = gps position data

$GPVTG = velocity data