This is an Arduino based guitar preamp+effector. This instructable contains basic information about how to build a circuit on a breadboard and an Arduino code to drive the system. The guitar effects are not implemented here, but some examples can be found from another project of mine: https://www.instructables.com/id/ATTiny44-Guitar-E...

This instructable will illustrate how to get the guitar signal properly through a biased input, and how to use weighted pins for output in order to get signal resolution higher than 10-bits.

Step 1: What You Need for the Circuit

This is everything you need for the breadboard circuit. The list of material will include:

LM386
any Op-amp (I used what I had at the moment)
2 x 10k resistors
1 x 10 ohm resistor
1 x 1k resistor
1 x 1.2k resistor
1 x 1.5k resistor
1 x 30k resistor
1 x 390k resistor
1 x 10k potentiometer
1 x 0.05 uF capacitor
1 x 0.1 uF capacitor
1 x 2.2 uF capacitor
1 x 47 uF capacitor
1 x 250 uF capacitor

The detailed resistor and capacitor values in the output stage is up to what headphone is going to be used. Also I heavily low-pass filtered the output sound, and different filter design can be experimented for better sound quality.

Step 2: Build the Circuit

Let's make the circuit on a breadboard. You will also need jumpers between the circuit and an Arduino.

Two output pins in the diagram goes to D5, D6
The input pin goes to A0
Vcc and GND from Arduino also connected to the circuit.
Guitar input pin is connected to a 1/4" jack.
The ground pin on the jack goes to ground in the circuit.
Output pin can simply be connected to a headphone with banana clips (or a regular headphone jack can be used)

Step 3: Code

And upload the code below to your Arduino.

void setup()
{

TCCR0B = TCCR0B & 0b11111000 | 1; TCCR0A &= ~B11; TCCR0A |= B011;

pinMode( 5, OUTPUT ); pinMode( 6, OUTPUT );

analogWrite( 5, 0 );

analogWrite( 6, 0 );

analogReference( DEFAULT );

_SFR_BYTE( ADCSRA ) &= ~_BV( ADPS2 );

_SFR_BYTE( ADCSRA ) |= _BV( ADPS1 );

_SFR_BYTE( ADCSRA ) |= _BV( ADPS0 );

}

void loop()

{

int input = ( (analogRead( 0 ) ) * 64 ) - 32768;

if(input>=65536) input = 65535;

if(input<0) input = 0;

unsigned short output = input + 32768;

analogWrite( 5, output >> 8 );

analogWrite( 6, output & 255 );

}

Note: this code is made based on http://pastebin.com/9zphwpvA

Step 4: Play the Guitar

Here is a sample of the preamp. More effects can be implemented by modifying the code in the loop(). For a few other examples please visit my other instructable: https://www.instructables.com/id/ATTiny44-Guitar-E...