Setup SSH Public Key authentication to login to a target

  • On your host machine, use ssh-keygen to generate an SSH key pair
    • ssh-keygen -t rsa
      • Follow the prompts
        • choose the <location> for the file
        • choose a <keyname> e.g. id_rsa_name_of_target
        • set a strong password to unlock the private key
        • default key-length is 2048-bits (don’t change if you do not understand what you are doing)
        • at the end of this process you will have a private/public keyfile <keyname> and a separate file with only the public key <>
      • N.B the private must never ever leave the host
      • Comprehensive information can be found at the link below information can be found at
  • Output the public key  in the format required by the target e.g. Open Media Vault v2.0 needs the public key to be output in RFC 4716 format
    • ssh-keygen -e -f </location/keyname>
  • Copy the public key to the target.
  • Use the host machine where the private key is stored to login to target server
    • ssh <user>@<IP address of target> -i <location>/<keyname>

Add USB audio (playback and mic) support to Raspberry Pi

Plug in USB audio card and boot Pi

dmesg | grep cm109
dmesg | grep Headphone
dmesg | grep C-Media
dmesg | grep General
dmesg | grep Jabra (*)

On Raspbian Stretch:

sudo nano /usr/share/alsa/alsa.conf

  1. defaults.ctl.card 0
  2. defaults.pcm.card 0

change 0 to 1


speaker-test -c2
sudo apt-get unstall mpg123

List audio devices

aplay -l

To force a specific device/sub-device use the command below

speaker-test -c2 -D plughw:1,0
aplay –device=hw:1,0 test.wav

alsamixer – c 1


arecord –device=hw:1,0 –format S16_LE –rate 44100 -c1 test.wav
aplay –device=hw:1,0 test.wav

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These companies supply project kits

Prepare an SDCard with Noobs for RaspberryPi

  • fdisk -l
  • insert card
  • fdisk -l
  • identity the device e.g. /dev/mmcblk0
  • fdisk /dev/mmcblk0
    • delete partitions (d)
    • list partitions (p)
    • create a partition (n)
    • change partions type (t)
      • use Hex code for fat32 is b
    • Make bootable (a)
    • write partition table (w)
  • format the partition
    • mkfs.vfat /dev/mmcblk0p1

download Noobs
sha256sum <filename>
unzip to partition created above

A very verbose and mega helpful guide can be found here


Nova Modem setup on Pi and using SMS capabilities

Activate hologram sim

Connect nova modem to pi

  • lsusb – should show modem detected as U-Blox device
  • – should show a number of u-blox tty devices
    • U-blox allows parallel execution of tasks.
  • Install the hologram library (wrapper over u-blox)
  • hologram modem -h
  • hologram modem type
  • hologram modem operator
  • hologram modem signal

Test cellular connectivity

  • ifconfig wlan0 down
    • bring down the wireless interface to ensure data is send over cellular
  • ping
    • fails
  • hologram modem connect
  • ifconfig (should show ppp0)
  • ping
    • succeeds
    • be cautious of data usage as connectivity is now over ppp over cellular
  • hologram modem disconnect
  • ifconfig wlan0 up

Test SMS

  • hologram send -h
  • hologram send –sms “message” –destination destination-number(use + format) –devicekey key
  • hologram receive –sms
    • waits for incoming messages

Using the hologram library