Arduino Guitar Pedal

Picture of Arduino Guitar Pedal

The Arduino Guitar Pedal is a digital multi-effect pedal based upon the Lo-Fi Arduino Guitar Pedal originally posted by Kyle McDonald. I made a few modifications to his original design. The most noticeable changes are the built-in preamp, and the active mixer stage which lets you combine the clean signal with the effects signal. I also added a sturdier case, foot switch, and rotary switch to have 6 discreet steps between the different effects.

The cool thing about this pedal is that it can be endlessly customized. If you don't like one of the effects, simply program another one. In this way, this pedal's potential is largely dependent upon your skills and imagination as a programmer.
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Step 1: Go get stuff

Picture of Go get stuff
You will need:

(x1) Arduino Uno REV 3 (Radioshack #276-128)
(x1) Make MakerShield Prototyping Kit (Radioshack #276-138)
(x3) 100K-Ohm Linear-Taper Potentiometer (Radioshack #271-092)
(x1) 2-Pole, 6-Position Rotary Switch (Radioshack #275-1386)
(x4) Hexagonal Control Knob with Aluminum Insert (Radioshack #274-415)
(x1) TL082/TL082CP Wide Dual JFET Input Op Amp (8-Pin DIP) (Radioshack #276-1715)
(x2) 1/4" Stereo Panel-Mount Audio Jack (Radioshack #274-312)
(x4) 1uF 63v capacitor (Radioshack #55047191)
(x2) 47uF 16v capacitor (Radioshack #55047280)
(x1) 100pF 50V 10% Hi-Q Ceramic Disc Capacitor (Radioshack #272-123)
(x1) 0.082µf 100V Mylar Capacitor (Radioshack #55046837)
(x1) 5pf 50V Ceramic Disc Capacitor (Radioshack #55047529)
(x6) 10K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #271-1335)
(x2) 1M Ohm 1/4-Watt Carbon Film Resistor (Radioshack #271-1356)
(x1) 390K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #55049555)
(x1) 1.5K Ohm 1/4W 5% Carbon Film Resistor (Radioshack #271-1120)
(x1) 510K Ohm 1/4W 5% Carbon Film Resistor (Radioshack #55049227)
(x1) 330K Ohm 1/4W 5% Carbon Film Resistor (Radioshack #44049468)
(x1) 4.7K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #271-1330)
(x1) 12K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #55049436)
(x1) 1.2K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #55049409)
(x1) 1K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #271-1321)
(x2) 100K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #271-1347)
(x1) 22K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #271-1339)
(x1) 33K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #55048044)
(x1) 47K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #271-1342)
(x1) 68K Ohm 1/4-Watt Carbon Film Resistor (Radioshack #55049451)
(x1) Heavy-Duty 9V Snap Connectors (Radioshack #270-324)
(x1) 90-Ft. UL-Recognized Hookup Wire (Radioshack #278-1221)
(x1) Enercell® Alkaline 9 Volt Battery (Radioshack #25-853)
(x1) Box 'BB' Size Orange Powder Coat (Small Bear #0301G)
(x1) DPDT Stomp switch (Small Bear #0203)
(x1) 1/8" x 6" x 6" rubber mat
(x1) 1/8" x 12" x 12" cork mat

Step 2: Header breakdown

Picture of Header breakdown
Break the male header strip down to fit properly in the Maker Shield kit.

An easy way to do this is to insert the end of the strip into each of the Arduino sockets and then snap off the excess pins. You will end up with 4 strips of proper size.

Step 3: Solder

Picture of Solder
Insert the male header pins into the Maker Shield and solder them into place.

Step 4: Template

Picture of Template
Print out the attached template on full-sheet adhesive paper.

Cut out each of the two squares.

(The file has the pattern repeated twice in case to optimize use of the paper, and in case you need an extra.)

Step 5: Drill

Peel off the backing of the adhesive template and stick it squarely on the front of the casing.

Drill all of the crosses with a 1/8" drill bit.

Starting from the left side, widen the first three holes with a 9/32" drill bit.

Widen the last hole of the top row with a 5/16" dill bit.

And then widen the singular hole in the bottom right with a 1/2" spade bit to finish off the front of the case.

Peel off the adhesive template from the front of the case.

Next, stick the next adhesive template to the back edge. In other words, stick it to the edge face most closely abutting the potentiometer holes.

Drill the crosses first with 1/8" holes and then widen them with larger 3/8" holes.

Peel away this template as well, and the case should be ready.

Step 6: Wire the pots

Picture of Wire the pots
Attach three 6" wires to each of the potentiometers.

For simplicity's sake, you should attach a black ground wire to the pin on the left, a green signal wire to the pin in the middle, and a red power wire to the pin on the right.

Step 7: Wire the Rotary Switch

Picture of Wire the Rotary Switch
Attach a 6" black wire to one of the inner pins.

Next, attach 6" red wires to the 3 outer pins both to the immediate left and right of the black inner pin.

To be sure you did this right, you may consider testing the connections with a multimeter.

Step 8: Build the circuit

Picture of Build the circuit
Start to build the circuit as pictured in the schematic. To see the schematic larger, click the little "i" in the upper right-hand corner of the image.

For now, while building the circuit, do not worry about the potentiometers, rotary switch, bypass switch, and input jacks.

To better understand what you are doing, this circuit consists of a few different parts:

The preamp uses one of the two op amps packaged in the TL082. The preamp is both boosting the guitar signal to line level and inverting the signal. When it comes out of the op amp the signal is split between the Arduino input and the "clean" volume knob for the mixer.

Arduino Input
The input for the Arduino was copied from Kyle's input circuit. It is basically taking the audio signal from the guitar and constraining it to roughly 1.2V, because the aref voltage within the Arduino has been configured to look for an audio signal in this range. The signal is then being sent to analog pin 0 on the Arduino. From here, the Arduino is then converting this to a digital signal using its built in ADC. This is a processor intensive activity and where most of the Arduino's resources are being allocated.

You can get a faster conversion rate and do more multiprocessing of the audio signal using timer interrupts. To learn more about that, check out this page on Arduino Real-Time Audio Processing.

The Arduino is where all of the fancy-shmancy digital signal processing is happening. I'll explain a bit more about the code later. For now, in relation to the hardware, what you need to know is that there is both a 100k potentiometer connected to analog pin 3 and a 6-position rotary switch connected to analog pin 2.

The 6-position rotary switch is functioning in a similar way to a potentiometer, but rather than sweeping through a resistance range, each pin has a discrete resistance associated with it. As you select different pins,  voltage dividers of different values are created.

Since the analog reference voltage had to be remapped to handle the incoming audio signal, it is important to use aref as the voltage source, as opposed to the standard 5V for both the rotary switch and the potentiometer.

Arduino Output
The Arduino output is only loosely based on Kyle's circuit. The part I kept was the weighted pin approach to get the Arduino to output 10-bit audio using only 2 pins. I stuck with his suggested weighted resistor ratings of 1.5K as the 8-bit value and 390K as the added 2-bit value (which is basically 1.5K x 256). From there I scrapped the rest. His output stage components were unnecessary because the audio was not going to an output, but rather to the new audio mixer stage.

Mixer Output
The effects output from the Arduino goes to a 100K pot connected to the audio mixer op amp. This pot is then used in conjunction with the clean signal coming from the other 100K potentiometer to mix the volume of the two signals together in the op amp.

The second op amp on the TL082 is both mixing the audio signals together, and inverting the signal once again to get it back in phase with the original guitar signal. From here the signal goes through a 1uF DC blocking capacitor and finally to the output jack.

Bypass Switch
The bypass switch toggles between the effects circuit and the output jack. In other words, it either routes the incoming audio to the TL082 and the Arduino, or skips all of this entirely and sends the input straight to the output jack without any altering. In essence, it bypasses the effects (and hence, is a bypass switch).

I have included the Fritzing file for this circuit if you want to look at it closer. The breadboard view and schematic view should be relatively accurate. However, the PCB view has not been touched and probably will not work at all. This file does not include the input and output jacks.

Step 9: Cut Brackets

Picture of Cut Brackets
Cut out two brackets using the template file attached to this step. They both should be cut out of non-conductive material.

I cut out the larger base bracket out of a thin cork mat and the smaller potentiometer bracket out of 1/8" rubber.

Step 10: Insert knobs

Picture of Insert knobs
Place the rubber bracket on the inside of the case so that it aligns with the drilled holes.

Insert the potentiometers up through the rubber bracket and the 9/32" holes in the case and lock them firmly in place with nuts.

Install the rotary switch in the same fashion in the larger 5/16" hole.

Step 11: Trim

Picture of Trim
If you use long shaft potentiometers or rotary switches, trim them down such that the shafts are 3/8" long.

I used a Dremel with a metal cutting wheel, but a hacksaw will do the job too.

Step 12: Switch

Picture of Switch
Insert the foot switch into the larger 1/2" hole and lock it in place with its mounting nut.

Step 13: Stereo jacks

Picture of Stereo jacks
We will be using stereo jacks for what is fundamentally a mono circuit. The reason for this is that the stereo connection will actually serve as the power switch for the pedal.

The way this works is that when mono plugs are inserted into each of the jacks, it connects the batteries ground connection (which is connected to the stereo tab) with the ground connection on the barrel. So, only when both jacks are inserted can ground flow from the battery to the Arduino and completed the circuit.

To make this work, first connect together the ground tabs on each jack with a short piece of wire.

Next, connect the black wire from the battery snap to one of the stereo audio tabs. This is the smaller tab that touches the jack about halfway up the plug.

Connect a 6" black wire to the other stereo tab on the other jack.

Lastly, connect a 6" red wire to the mono tabs on each of the jacks. This is the large tab that touches the tip of the male mono plug.

Step 14: Insert jacks

Picture of Insert jacks
Insert the two audio jacks into the two holes in the side of the case and lock them in place with their mounting nuts.

Once installed, check that none of the metal tabs on the jack are touching the body of the potentiometers. Make adjustments as necessary.

Step 15: Wire the switch

Picture of Wire the switch
Wire one of the outer pairs of the DPDT stomp switch together.

Wire one of the jacks to one of the center pins on the switch. Wire the other jack to the other center pin.

Connect a 6" wire to each of the remaining outer pins on the switch.

The wire that is in line with the jack on the right should be the input. The wire that is in line with the switch on the left should be the output.

Step 16: Finish the wiring

Picture of Finish the wiring
Trim the wires attached to the components installed inside the case to remove any slack before you solder them to the Arduino shield.

Wire them to the Arduino shield as specified in the schematic.

Step 17: Cork

Picture of Cork
Affix the cork mat to the inside of the case's lid. This will keep the pins on the Arduino from getting shorted on the metal of the case.

Step 18: Program

Picture of Program
The code that this pedal is largely built upon ArduinoDSP which was written by Kyle McDonald. He did some fancy things like mess around with the registers to optimize the PWM pins and change the analog reference voltage. To learn more about how his code is working, check out his Instructable.

One of my favorite effects on this pedal is a slight audio (distortion) delay. I was inspired to try creating a delay line after seeing this really simple code posted on Little Scale blog.

The Arduino was not designed for real-time audio signal processing and this code is both memory and processor intensive. The code that is based on the audio delay is especially memory intensive. I suspect the addition of a stand-alone ADC chip and external RAM will greatly improve the ability for this pedal to do awesome things.

There are 6 spots for different effects in my code, but I have only included 5. I have left a blank spot in the code for you to design and enter your own effect. That said, you can replace any slot with any code that you wish. However, keep in mind that trying to do anything too fancy will overwhelm the chip and keep anything from happening.

Download the code attached to this step.

Step 19: Attach

Picture of Attach
Attach the Arduino to the shield inside the case.

Step 20: Power

Picture of Power
Plug in the 9V battery to the 9V battery connector.

Carefully situate the battery snugly between the DPDT switch and the Arduino.

Step 21: Case closed

Picture of Case closed
Put the lid on and screw it shut.

Step 22: Knobs

Picture of Knobs
Place knobs onto the potentiometer and rotary switch shafts.

Lock them in place by tightening the set screws.

Step 23: Plug and play

Picture of Plug and play
Plug in your guitar to the input, connect an amp to the output, and rock out.
lhörst5 hours ago

I'm not 100% sure where i'm supposed to be wiring the input and output jacks to, unless it doesn't really make a difference. I have them on either side of the pushbutton but it doesn't appear to make a difference which side i connect them too.

I'm also testing mine with an oscilliscope and a function generator, if you could tell me what i'm supposed to be seeing to make sure i did it right that would be awesome!

Nithrate14 days ago

Have you tried using a Bass guitar instead of a guitar? It just sounds too fuzzy

danejo3 months ago

For those of you having trouble following the corrections needed to make the pedal work, here is a veroboard layout I made. With this you can also create the circuit without the Arduino shield.

I've been following this tutorial and I've some issues with the code, I already changed the "WProgram.h" and "WConstants.h" with "Arduino.h" but I still get some errors:

dsp.cpp: In function 'void output(int, short int)':
dsp.cpp:23: error: 'OCR2B' was not declared in this scope
dsp.cpp:24: error: 'OCR2A' was not declared in this scope

I'm using Arduino 1.0.3 and my board is an Arduino Leonardo

i have the same problem but start's with analogWrite not declared in scoop

use version 20
STARDEMOS3 months ago

jwestenberg4 months ago
I really want to make this, but since there are so much revisions that are only mentioned in the comments I don't think I can get it to work. I think it would really help if this instructable would be revised or someone would make a new working instructable.

aballen5 months ago
Can I use a TL072 for this(I have these on hand)
randofo (author)  aballen5 months ago
I see no reason why it should not work, but I cannot be 100% certain.
aslaine5 months ago
hello there i'm currently trying to make this project but whenever i try to verify the code and then upload it to the arduino it gives me errors...Does anyone has the same problems as me or knows what to do?
fightdu5 months ago
i have been searching for octive pedel coding specifically down or bass octive .also does it matter if i use arduino mini or ,nano ?
aloriedo6 months ago
Ok guys, I'm plannig to build this pedal... But, how does it actually sounds? And is it easy to build? Can I use my Arduino Leonardo to build it?
X1L37 months ago
I think the only reason most of your projects aren't working is because you're uploading the code with a later version of arduino. I just spent the afternoon on this and like a lot of others i had clean audio but no output from the atmega. So i downloaded arduino 0020 and uploaded the code with that. No need to rename libraries etc. Just open the code here and that's it. Providing your circuit is ok it'll work. It's very very dirty and very lo-fi. Which is cool by me. Awesome for synth basslines and drums. Stick a clean 808 through it and you've got instant raggacore.

Hope this helps. I spent hours going over the circuit, swapping chips, trying different caps and resistors etc. This is all it was though.

improCJB7 months ago
Hey there! I am currently working on building this pedal. I have a question about it and I was hoping I could get some feedback or clarity of information. My question is, what do the 3 potentiometers and the rotary switch do. Like what are their functions when the pedal is up an running? If you shed light on this subject that would be very helpful and greatly appreciated! Im looking forward to creating this pedal!
jservin18 months ago
I have made this with a breadboard and I get no effects running through. I am using the arduino rev 3 and tried using arduino 20 as well. I get clean guitar through and have checked all my wiring and polarity on the breadboard, everything looks good. I am thinking either the arduino is deffective or the code isnt processing right even though I followed all the instruction to the T. I even changed Wprogram.h and Wconstants.h in the code. Is there anything i am missing that should be done to the code specifically for a rev 3 arduino?
jreeg9 months ago
I recently finished putting everything together, and I get no sound out of the arduino. I've checked and re-checked my connections according to the schematic with a multimeter, and everything looks to be in order, but still I get nothing.

Is this a software problem? I only modified the Wprogram.h and Wconstants.h to both be arduino.h in the code.

Would soldering the resistors in the wrong order on the rotary switch cause a problem? Because that's the only other thing I can think of.
CyrilHaumont10 months ago
Great work, I'm doing mine version of this guitar pedal with a different preamp and output, but i have just one problem :
I can't find Wprogram.h and Wconstants.h, i read all comments and nobody seems to have this probleme.
Is it about my version of arduino ide ? (i didnt dl version 20 yet)
replace both with "Arduino.h" and it should take care of the problem
csmith1529 months ago
Hi, so I have put together the circuit and and I am in the process of testing it. I am getting a clean signal out, however it seems as tho no effected signal is being sent from the Arduino. Can anyone offer me any help? I am not sure if the rotary switch is doing nothing because there is no effected signal coming out but having a little issue with that as well.

I have worked on including a small display to show which effect is selected. I got the rotary switch to work with the display without including the audio/op amp. However when I include the display with the rest of everything it does not work.
I am more concerned about getting the effects to work more than the display.

Any help is much appreciated!!!
BassPab10 months ago
Can you also use this for your bass?
jchhebson11 months ago
I don't know why, but I'm still unable to find the template to download.
BenBurge11 months ago
What exactly do each knobs/rotary switch do? You do an awesome job coving the build part of the project, but i'd really love to see the final product!
jreeg11 months ago
I'm going to be putting this together in a few days when the parts come in the mail, and I noticed that the templates for all the drilling on the project box and for cutting out the brackets aren't actually attached to their steps. Just something I thought you might want to know. Thanks!
Richard Zusak11 months ago
I hear the clean sound, but none of the fx effects. Even I try to make the program with only one effect without array, but doesnt seem to work. Also I tried to change the resistors and capacitors and others things as said in the comments below but nothing. Any idea of what can it be? Thanks for reading.
randofo (author)  Richard Zusak11 months ago
Which effect are you trying?
BenBurge11 months ago
Would this work with the Arduino Nano?
I'm thinking of building on internally!
Richard Zusak11 months ago
Is it necessary a preamp for this project? I actually have the same issue as everyone here about the clean sound, Does any one have found a solution?
randofo (author)  Richard Zusak11 months ago
The TL082 is the preamp. Everyone is having different problems. Can you be more specific. Are you hearing or not hearing clean sound?
ianfantry11 months ago
Does anyone know if this works with the Rev 2 board? I've constructed the circuit, but I am having trouble generating the effects. I am getting a clean signal to my amp so I know the preamp stage is working. Anyone else having this issue with a Rev 2?
Probably a lot easier thatn all the other ones....
can a single pole rotary switch be used for this?
Brilliant. Thank you so much, I am building a pickup replacer pedal at the moment I'll post the results when done.
keltroth1 year ago
Small Bear links are broken
Box :
Stomp switch :

Very nice Instructs !!

Thank you !
Brewdawg2 years ago
Please forgive my ignorance, but where is the template for drilling the holes? It's not in the full pdf file and I don't see a link.

randofo (author)  Brewdawg2 years ago
Ack. I forgot to upload it. I don't have the file on this computer, but I should be able to get it online tomorrow.
Also the file for the fritz.??? any chance you can upload that?
randofo (author)  athompson2112 years ago
It is already attached to Step 8
yes it is but when i click on it, it doenst pull anything up but a much of gibberish!
randofo (author)  athompson2112 years ago
It is probably getting renamed. Just rename it back to ArduinoPedal.fz

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