Raspberry Pi

The first approach to the microcomputer choice was analyzing the Locustream Box. They used a PC Engines 500 MHz AMD Geode LX800 using Gentoo Linux distribution[9].

This hardware was sufficient for what we need. The problem is that it would be needed to order the different parts and put them together, plus the total cost is around 150€. For us this seemed to be a major problem to a project that wants to grow spontaneously under the individual motivation. The Raspberry Pi is a credit-card-sized single-board computer developed in the UK by the Raspberry Pi Foundation with the intention of promoting the teaching of basic computer science in schools. It has an ARM1176JZF-S 700 MHz processor VideoCore IV GPU, and 512 megabytes of RAM. It does not include a built-in hard disk or solid-state drive, but uses an SD card for booting and long-term storage.

The Raspberry Pi presents a solution for most of our needs. It is quite cheap, it is already built, and it has a very enthusiastic community working to develop the hardware and system. Most of them, around the Pure Data on Rasperry, a fundamental tool for our project.

USB ADC

The Raspberry PI does not have an analogic input, so it is necessary a USB sound card. Not all the USB Analog to Digital Converters work with the Raspberry Pi and it´s important to slow down the speed device to 1.1 adding

$>> dwc_otg.speed=1

to the string in the file /boot/cmdline.txt.

As we are only using the computer as a listening point, we change the USB ADC to default changing the /etc/modprobe.d/alsa-base.conf file replacing the

$>> options snd-usb-audio index=-2

string to

$>> options snd_bcm2835=-2

and creating a /.libao in the home directory with

$>> driver=alsa

$>> dev=default

strings.

Electret Microphone

This is a critical point, because it is very complicated to found a microphone that resists to the weather conditions and with an enough small size to put in places like windows or breathers and not expensive enough to be in a public place. We decide to use the Peter Sinclair suggestion for the Locus Sonus Project with a DIY microphone, Figure1, that only needs 5v power (perfect for the USB connections) using a electret microphone.[12]

HARDWARE