Based on my desire to make a multiple guitar effect, A guitar effect is an instrument that can change the output signal from guitar.
For that purpose in this project i'm using raspberry pi which acting as a DSP (Digital Signal Processing) . Inside raspberry pi actually a small linux computer ,an installed software like Pure data extended process input signal from the guitar and(using USB sound card) creating processed output signal to the guitar amplifier. The main advantages is you can make you own guitar effect from scratch in your on way.
This Project mainly inspired by:
1. http://insidetheseboxes.wordpress.com/2012/10/07/pd-extended-in-raspbian-wheezy-armhf/
2. http://ampbrownie.com/
3. http://guitarextended.wordpress.com/

Step 1: Part List

Main Part
1.Raspberry Pi
2. USB sound Card
3.SD card
4.Guitar + cable
5. Usb cable/USB power supply

6. USB keyboard and mouse
7. Display

Optional Part

1. USB to RCA
2. USB mini card reader
3. RJ45 LAN cable + router (optional)

Please see some comments in picture fore more detail

Step 2: Preparation

Initial preparation. Prepare at least 4 GB SD card and then do the following
note: if you buy raspbian SD card you can skip this step

1. Formatting the SD card
Install SD formatter for formating SD card ,To get this program can be obtained from link below
https://www.sdcard.org/downloads/formatter_4/

2. Installing Rasberry Pi program
Download Rasbian from
http://www.raspberrypi.org/downloads and un-zip make an *.img file

to install raspbian wheezy using win32 Disk imager from
sourceforge.net/projects/win32diskimager/

if you still confused reffer this link fore refference http://learn.adafruit.com/adafruit-raspberry-pi-lesson-1-preparing-and-sd-card-for-your-raspberry-pi
After finish Put the SD memory to rasrberry pi

Step 3: The First Try

Do follwing step
1. After the an linux in the microSD card put in the adapter and place it in the raspberry pi.
2. connect to display connection i use RCA connection via USB to RCA so i can see in my laptop, you can also use HDMI display output, RCA output to monitor/television
3. Connect USB keyboard and USB mouse to raspberry pi USB port.
4. Connect to raspberry pi LAN port using LAN cable to router.
5. Connect to 5 V dc power supply

and see the blink LED at upper right corner of your raspberry if successful you will prompt to raspberry configuration
1. Expand the SD card(choise1)
2. Enable at boot to desktop(choice 3)

more detail for this setup http://learn.adafruit.com/adafruits-raspberry-pi-lesson-2-first-time-configuration

If you lucky it will show in the last image , congratulation

Step 4: More Detail Setup for Guitar Effect

Remote using SSH and vnc server

http://learn.adafruit.com/adafruits-raspberry-pi-lesson-3-network-setup
http://learn.adafruit.com/adafruits-raspberry-pi-lesson-6-using-ssh
http://learn.adafruit.com/adafruit-raspberry-pi-lesson-7-remote-control-with-vnc

note:
sudo ifconfig
sudo vncserver

Install Pure Data extended
http://insidetheseboxes.wordpress.com/2012/10/07/pd-extended-in-raspbian-wheezy-armhf/

install usb sound card some problem with raspberry that request USB 1 specification it means that after connection your keyboard and mouse will not work that why we use ssh/vncserver

code for down grade is
sudo nano /boot/cmdline.txt
dwc_otg.speed=1

note :if you have problem how to get back to USB 2 put sd card into your PC using USB to sdcard and modified /boot/cmdline.txt by removing dwc_otg.speed=1

Step 5: Try the Sound

A little bit tricky to make Raspberry pi to work because USB 1 for sound card but i still made it. After a month of no result
you will see how it working

http://youtu.be/eK1y0LYqitA

sorry for bad video recording!!

DIY Guitar effect using Raspberri Pi - Step #5
Download

Step 6: Future Development

My own pd software
Raspberry pi Head less
Usb Midi controller

Step 7: USB MIDI Controller (update 21-11-2014)

USB MIDI controller that I use is KORG Nanocontroler.

I assign the midi for each effect you Can see this midi device is working in sound test. If you pressed the a key, it will lit the led and also send message to pure data at Raspberry pi see changing value every time you pressed.

Step 8: Wolfson Audio Soundcard

After changing/ buying from 1 $ to 50 $ I have some problems with USB 1.1 it resulting not quite good result. and make the USB not working is pain in the ... .

I decided to buy this sound card that use all the external pin (GPIO) well.