Introduction: Raspberry Pi Zero Guitar Pedal

By ElectroSmash
About: We are MAD about guitar pedals.

Pedal-Pi is a lo-fi programmable guitar pedal that works with the Raspberry Pi ZERO Board. The project is totally Open Source & Open Hardware and made for hackers, programmers and musicians that want to experiment with sounds and learn about digital audio.

You can code your own effects using standard C and get inspiration from the ready-to-use effects from the forum, like the Clean/Transparent, Booster/Volume, Distortion, Fuzz, Delay, Echo,Octaver, Reverb, Tremolo, Looper, etc.

Specifications.

  • Based in Raspberry Pi Zero (1GHz ARM11 core).
  • Analog stages using MCP6002 rail-to-rail operational amplifier.
  • ADC: 12bits / Sampling Rate 50Ksps (MCP3202).
  • Output Stage: 12 bits (2x6bits PWMs running in parallel)
  • Pi Zero:
    • 1GHz ARM11 core.512MB of LPDDR2 SDRAM.
    • Micro-SD card slot.
  • Interface:
    • 2 Configurable push buttons.
    • 1 Configurable toggle switch.
    • 1 programmable blue led
    • .True Bypass Foot-switch.
  • Connectors:
    • Input Jack, 1/4 inch unbalanced, Zin=1MΩ.
    • Output Jack, 1/4 inch unbalanced, Zout=100Ω.
    • Power supply: power taken from the Pi Zero board (micro-USB).

Step 1: Step 1: Get the Components and the PCB.

The electronic components are all through-hole and easy-to-find. You can see the complete list of components here:

For the PCB you can find in the forum a PDF with the transfer files so you can do the PCBs at home, also in the EletroSmash Store there are PCBs for sale:

Attachments

Step 2: Step 2: Soldering the Circuit.

There is manual that explains how to build the Pedal-Pi step by step with photographs and detailed information:

There is a topic in the forum for any additional question.There is also a Flickr gallery with high-res photos of each step.

Attachments

Step 3: Step 3: a Closer Look to the Circuit.

There is a detailed analysis of the Pedal-Pi Circuit in the forum:

This hat has three parts:

  • The Input Stage: Amplifies and filters the guitar signal making it ready for the ADC (Analog do Digital Converter). The ADC sends the signal to the PI ZERO using SPI communication. In the forum the topic "Using MCP3202 ADC with Raspberry Pi Zero" gives more details about the ADC-Pi ZERO connection.
  • Pi ZERO: It takes the digitalized audio waveform from the ADC and does all the Digital Signal Processing (DSP) creating effects (distortion, fuzz, delay, echo, tremolo...). In the forum the topic "Basics of Audio DSP in C for Rapsberry Pi Zero" can assist you to learn the basics.
  • The Output Stage: Once the new digital waveform is created, the Pi Zero creates an analogue signal with two PWMs combined, the signal is filtered and prepared to be sent to the next pedal or the guitar amp. For more info check the topic "PWM Audio on Raspberry Pi Zero".

Step 4: Step 4: Start Programming!

Check the "How to Start Programming Pedal-Pi" guide. It is a short guide to start coding this Raspberri Pi Zero guitar pedal. The aim is to understand the basic ideas and then progress as fast as possible through a series of examples.

You are very welcome to upload your ideas and pedals to the forum!

Step 5: Step 5: Create Your Own Sounds.

The best way to progress is to take the basic examples from the forum and try to modify them to fit your taste or set-up. Just changing some values or parameters can make a great difference.

Once you have understood the basic examples, you can think about how to create your own new pedals (reverse delay? reverse-echo?) or mixing some of the examples (fuzz+echo? distortion+delay?). There are tons of unexplored effects to be discovered ;) !

There is a cool review by Blitz City DIY in YouTube: Pedal Pi Kit Review - A Raspberry Pi Zero Guitar Pedal

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