Make:

/* Stereo BeatGen v1 - originally written by Loud Objects for the ATTiny85/NOISE TOY projects loudobjects.com - adapted/messed with for Arduino by Collin Cunningham me [at] collinmel.com assumes pins 3 & 4 connected to left & right audio momentary switches between 8 & 9 and GND */

unsigned long NextRandom = 1;
unsigned long Bass_Start = 300, Bass_End = 600;
unsigned char Last_Val_Left = 1, Last_Val_Right = 1;
unsigned long Bass_Left_Period = Bass_Start, Bass_Right_Period = Bass_Start;
unsigned long Bass_Left_Sample = 1, Bass_Right_Sample = 1;
unsigned char Bass_Left_On = 1, Bass_Right_On = 1;
unsigned char Snare_Left_On = 1, Snare_Right_On = 1;
unsigned char Snare_Left_Sample = 1, Snare_Right_Sample = 1;
unsigned long Tempo_Period = 1200, Tempo_Outer = 1, Tempo_Sample = 1;
unsigned char Trax_Left[] = {
1, 2, 3, 0, 3, 2, 0, 1};
unsigned char Trax_Right[] = {
2, 1, 0, 3, 1, 3, 0, 2};
unsigned char Track_Index = -1;
unsigned long New_Rand = randomGen();
unsigned long NextRandom2 = 1;
unsigned long Snare_Length = 500;

void setup()
{
// SET PINS 3 AND 4 AS OUTPUTS
pinMode(3, OUTPUT);
pinMode(4, OUTPUT);
pinMode(2, INPUT);

// SET PULL-UP RESISTORS ON PINS 9 AND 8
pinMode(9, INPUT);
pinMode(8, INPUT);
digitalWrite(9, HIGH);
digitalWrite(8, HIGH);
digitalWrite(5, LOW);

}

void loop(){

NextRandom2 = NextRandom2 + 9;
New_Rand = NextRandom2;

// UPDATE SAMPLES
if (Bass_Left_On)
{
if (!(--Bass_Left_Sample))
{
if ((Bass_Left_Period += 11) > Bass_End)
{
Bass_Left_On = 0;
}
Bass_Left_Sample = Bass_Left_Period;
Last_Val_Left = 1 - Last_Val_Left;
}
}

if (Bass_Right_On)
{
if (!(--Bass_Right_Sample))
{
if ((Bass_Right_Period += 13) > Bass_End)
{
Bass_Right_On = 0;
}
Bass_Right_Sample = Bass_Right_Period;
Last_Val_Right = 1 - Last_Val_Right;
}
}

if (Snare_Left_On)
{
if (!(--Snare_Left_Sample))
{
Snare_Left_Sample = New_Rand / 200;// % 10;
Last_Val_Left = 1 - Last_Val_Left;
}
if (!(--Snare_Length))
{
Snare_Left_On = 0;
}
}

if (Snare_Right_On)
{
if (!(--Snare_Right_Sample))
{
Snare_Right_Sample = New_Rand / 200;// % 10;
Last_Val_Right = 1 - Last_Val_Right;
}
if (!(--Snare_Length))
{
Snare_Right_On = 0;
}
}

// CHECK FOR NEXT BEAT
if (!(--Tempo_Outer))
{
Tempo_Outer = 10;
if (!(--Tempo_Sample))
{
if (++Track_Index == 8)
Track_Index = 0;

Tempo_Sample = Tempo_Period;
Bass_Left_On = (Trax_Left[Track_Index] & 1);
Bass_Right_On = (Trax_Right[Track_Index] & 1);
Snare_Left_On = (Trax_Left[Track_Index] & 2);
Snare_Right_On = (Trax_Right[Track_Index] & 2);
Snare_Length = 5000;
Bass_Left_Period = Bass_Start;
Bass_Left_Sample = 1;
Bass_Right_Period = Bass_Start;
Bass_Right_Sample = 1;
}
}

// OUTPUT
if (Last_Val_Left)
PORTD |= (1 << 3);
else
PORTD &= ~((1 << 3));
if (Last_Val_Right)
PORTD |= (1 << 4);
else
PORTD &= ~((1 << 4));

// BUTTON INPUT CHECKS
//pin 8 for tempo
if ((digitalRead(8)) == LOW)
{
randomSeed(analogRead(0));
Tempo_Period = (random(1627) / 15 * 25); // experiment with diff values for better range
}
//pin 9 for beat
if (digitalRead(9) == LOW)
{
unsigned char i;
for (i = 0; i < 8; i++)
{
Trax_Left[i] = randomGen();
Trax_Right[i] = randomGen();
}
}
}

unsigned long randomGen(void) //pseudo random from original sketch
{
NextRandom = NextRandom * 3865 + 131;
return ((NextRandom >> 16) & 32767);
}