discussion / Sensors  / 5 March 2016



I’m sure you are all aware of the different open source hardware that has become available. These are lightweight small computers that are designed to allow anyone from programmers, hobbyists to school children to start creating.

The RaspberryPI is right up there and has been making some great new versions and setting some amazing records at the same time. The latest 2 versions that have appeared are the PI Zero that costs $5 and is the first computer to be given away on the front of a magazine. This sounds like a gimmick and yes it was a publicity stunt of sorts but it was about the most thought provoking one I have seen in a long time when you think about the implications of a computer that can be given away and the possibilities this opens up. Not only in terms of 3rd world applications but also of the uses for monitoring where a little processing power is needed.

The latest kid on the block is the RaspberryPI3 that has added the long awaited WiFI, Bluetooth 4.1 and BLE. As you can see from the spec below there are lot of possibility that the new PI can be put to.

The Raspberry Pi 3 is the third generation Raspberry Pi.

  • A 1.2GHz 64-bit quad-core ARMv8 CPU
  • 802.11n Wireless LAN
  • Bluetooth 4.1
  • Bluetooth Low Energy (BLE)

Like the Pi 2, it also has:

  • 4 USB ports
  • 40 GPIO pins
  • Full HDMI port
  • Ethernet port
  • Combined 3.5mm audio jack and composite video
  • Camera interface (CSI)
  • Display interface (DSI)
  • Micro SD card slot (now push-pull rather than push-push)
  • VideoCore IV 3D graphics core

The Raspberry Pi 3 has an identical form factor to the previous Pi 2 (and Pi 1 Model B+) and has complete compatibility with Raspberry Pi 1 and 2.

If you are looking for a small computer you should check out the whole family at https://www.raspberrypi.org/

And don't forget the Raspberry Pi Zero! It's a tiny version with stripped back connectivity and performance but still capable of running a full proper OS:


Low power demands mean it'd be easy to run off solar or batteries, and the same array of GPIO connections as the big brother Pi make extending it very possible.

I am not sure how to word my questions so bare with me...

Is there a way to connect a raspberry pi to a recording device such as an acoustic recorder then use it to upload the information the recorder collects directly to the cloud? I'm not picturing this occuring simultaneously with recording but more like at the end of the day...or at regularly scheduled intervals.

Here's one idea to do somethig that might be useful. The original artical can be found at http://sonof8bits.com/automated-raspberry-pi-audio-recorder/2014/09

Looks straight forward enough to do :)

This tutorial will show you how to build a fully automated recorder using an RPi, a USB sound card and a USB drive.

First up; install Raspbian, make sure it defaults to the command line and/or has SSH access so you can login to it from another computer. There’s plenty of tutorials out there explaining how to do this.

Second; make sure you have a compatible sound card, (I used a spare Griffin iMic, any class compatible one should work) and a USB flash drive. It should be possible to write to the SD card you’re using on the RPi, but people have had problems going that route. Besides, using a fat32 formatted usb drive will ensure you can plug it into you computer and play or copy the sound files without having to login (ssh) to the RPi.

First we’re gonna get rid of a lot of unwanted stuff! This isn’t a complete list, but I’m sure we can live without these applications installed taking up precious CPU cycles, RAM and disk space. Note: This will completely wipe the graphical user interface. You won’t be able to use the desktop anymore!

$ sudo apt-get purge galculator idle3 idle idle-python3.2 python3 midori scratch xpdf midori dillo netsurf-common netsurf-gtk leafpad penguinspuzzle pistore gpicview heirloom-mailx wpasupplicant aptitude xarchiver omxplayer aspell usbmuxd debian-reference-common debian-reference-en python-picamera cups-bsd cups-common vim-common vim-tiny desktop-base lightdm lxappearance lxde-common lxde-icon-theme lxinput lxpanel lxpolkit lxrandr lxsession-edit lxshortcut lxtask lxterminal obconf openbox raspberrypi-artwork xinit xserver-xorg xserver-xorg-video-fbdev xserver-common xserver-xorg-core xserver-xorg-video-fbturbo x11-common x11-utils x11-xkb-utils xauth xfonts-encodings xfonts-utils oracle-java7-jdk aptitude-common python python-gi python-minimal python-pifacecommon python-pifacedigitalio python-rpi.gpio python-serial python-support python2.7 python2.7-minimal python3.2 python3.2-minimal

Followed by:

$ sudo apt-get autoremove


$ sudo apt-get autoclean

That’s a lot of stuff we won’t be using! Now, we’re gonna install what we do want:

$ sudo apt-get install sox libsox-fmt-mp3

Sox is a specialized recording, processing and playback application. I won’t go into it too much, but it fits our needs perfectly. The second, libsox-fmt-mp3, is a library so we can encode to MP3 (if that’s what you want).

Now that we deleted and installed what we need, let’s set-up the soundcard. First up, let’s kill the built-in sound card:

$ sudo nano /etc/modules

And comment out:


By putting a “#” in front of it. Like so:

# snd-bcm2835

To be sure USB is first in line, we’re gonna force ALSA to pick it over the built-in one, even if we’ve just killed it.

$ sudo nano /etc/modprobe.d/alsa-base.conf

And comment out:

options snd-usb-audio index=-2

Again, with a “#” like this:

# options snd-usb-audio index=-2

Last but not least enter:

$ alsamixer

And set the recording levels of your soundcard to how you like them by pressing F4. To make sure the Raspberry Pi always boots up with these sound settings, enter this in the command line:

$ sudo alsactl store

Make a folder to mount the USB stick in:

$ sudo mkdir /mnt/USB/

Now we’re gonna make a few scripts. Don’t be afraid if you’ve never done this before, I’ve pre-fabricated them for you! In your home folder (Type “cd” and hit enter if you’re not certain), type:

$ mkdir Scripts

This’ll make a neat little folder for you to put scripts in. Change into it by typing:

$ cd Scripts/


$ nano MyBoot.sh

Copy and paste the following into it.

## Created by Son of 8-Bits
## http://sonof8bits.com/
## Borrowing parts from Autostatic
## http://autostatic.com/

## Mount the USB stick and kill unwanted services

## mount the USB stick
sudo mount -t auto /dev/sda1 /mnt/USB

## Stop the ntp service
sudo service ntp stop

## Stop the triggerhappy service
sudo service triggerhappy stop

## Stop the dbus service. Warning: this can cause unpredictable behaviour when running a desktop environment on the RPi
sudo service dbus stop

## Stop the console-kit-daemon service. Warning: this can cause unpredictable behaviour when running a desktop environment on the RPi
sudo killall console-kit-daemon

## Stop the polkitd service. Warning: this can cause unpredictable behaviour when running a desktop environment on the RPi
sudo killall polkitd

## Kill the usespace gnome virtual filesystem daemon. Warning: this can cause unpredictable behaviour when running a desktop environment on the RPi
killall gvfsd

## Kill the userspace D-Bus daemon. Warning: this can cause unpredictable behaviour when running a desktop environment on the RPi
killall dbus-daemon

## Kill the userspace dbus-launch daemon. Warning: this can cause unpredictable behaviour when running a desktop environment on the RPi
killall dbus-launch

## Set the CPU scaling governor to performance
echo -n performance | sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor


Press “ctrl+x” to exit, “Y” to save, followed by an enter. You should now be back in the command line. This script will automatically mount your USB drive in /mnt/USB/ and kill some unwanted services clogging up RAM and CPU cycles. Most of this script was made by Autostatic, check out his original work here.

Now for the recording script:

$ nano Record.sh


## Created by Son of 8-Bits
## http://sonof8bits.com/
## 48000Hz stereo MP3 at 320kbps that automatically stops recording after 1 minute of silence.

FILENAME=$(date +”%Y%m%d_%H%M”)

sudo rec -c 2 -r 48000 -C 320.99 –buffer 262144 /mnt/USB/${FILENAME}.mp3 silence 1 0.1 1% 1 1:00 1%

[ $? -eq 0 ] || exit $?

sleep 10

sudo shutdown now


ctrl+X, Y, enter

To make these scripts work as planned enter:

$ sudo chmod 755 MyBoot.sh Record.sh

But these scripts won’t start by themselves just by being there! To make them start at boot type:

$ sudo nano /etc/rc.local

On the empty line after “# By default this script does nothing.” add:

sudo /home/pi/Scripts/MyBoot.sh
sudo /home/pi/Scripts/Record.sh

ctrl+X, Y, enter

BAM! You’re done!

Try it out by hooking up a sound source to the line-in of your soundcard, booting the Pi, and recording a part of whatever it is you want to record. Note that after one minute of silence the RasPi will shut itself down. Listen back what you’ve just recorded by unplugging the USB flash drive and plugging it in you computer. Here are some tips if things are not to your liking.

Volume too low or high? Check the part about Alsamixer. (And don’t forget to check the level coming out of your audio source as well!)
Like to stop sooner (or later) after silence sets in, edit the recording script. See the part that says “1:00”? This is 1 minute, edit it to your liking. For instance ‘0:30’ for 30 seconds or ‘2:00’ for 2 minutes.
Pi not getting enough power? Use a 2 ampere powerplug or put a powered USB-hub between the RasPi and the soundcard/USB stick.

Hi Courtney,

I'm also looking for suitable mics for a Pi-based recorder (see https://www.wildlabs.net/community/thread/188 and https://www.wildlabs.net/community/thread/169).  I've found that the cheaper USB mics have fixed sampling rates, e.g. this one http://www.maplin.co.uk/p/desktop-dynamic-microphone-a99jb which only records at 44k.  That's a problem if you don't need high frequencies (e.g. recording tiger roars) and are restricted by storage space in the field - particularly if you want to do remote download!  An alternative that I'm trying is to use an audio USB interface like the Behringer UCA222 which connects to an analog mic and samples down to 11k.

I'll be testing different analog mics for sensitivity and noise and report back.  Let me know if you have any other ideas too.