distortion.c

// CC-by-www.Electrosmash.com open-source project.
// distortion.c effect pedal, the input signal change is clipped depending on the PUSH1/PUSH2 buttons. 

#include <bcm2835.h>
#include <stdio.h>

// Define Input Pins
#define PUSH1 			RPI_GPIO_P1_08  	//GPIO14
#define PUSH2 			RPI_V2_GPIO_P1_38  	//GPIO20 
#define TOGGLE_SWITCH 	RPI_V2_GPIO_P1_32 	//GPIO12
#define FOOT_SWITCH 	RPI_GPIO_P1_10 		//GPIO15
#define LED   			RPI_V2_GPIO_P1_36 	//GPIO16

uint32_t read_timer=0;
uint32_t input_signal=0;
uint32_t output_signal=0;
uint32_t distortion_value=100; //good value to start.

uint8_t FOOT_SWITCH_val;
uint8_t TOGGLE_SWITCH_val;
uint8_t PUSH1_val;
uint8_t PUSH2_val;

int main(int argc, char **argv)
{
    // Start the BCM2835 Library to access GPIO.
    if (!bcm2835_init())
    { printf("bcm2835_init failed. Are you running as root??\n");
      return 1;}
	// Start the SPI BUS.
	if (!bcm2835_spi_begin())
    {printf("bcm2835_spi_begin failed. Are you running as root??\n");
      return 1;}
	
	//define PWM	
    bcm2835_gpio_fsel(18,BCM2835_GPIO_FSEL_ALT5 ); //PWM0 signal on GPIO18    
    bcm2835_gpio_fsel(13,BCM2835_GPIO_FSEL_ALT0 ); //PWM1 signal on GPIO13    
	bcm2835_pwm_set_clock(2); // Max clk frequency (19.2MHz/2 = 9.6MHz)
    bcm2835_pwm_set_mode(0,1 , 1); //channel 0, markspace mode, PWM enabled. 
	bcm2835_pwm_set_range(0,64);   //channel 0, 64 is max range (6bits): 9.6MHz/64=150KHz switching PWM freq.
    bcm2835_pwm_set_mode(1, 1, 1); //channel 1, markspace mode, PWM enabled.
	bcm2835_pwm_set_range(1,64);   //channel 0, 64 is max range (6bits): 9.6MHz/64=150KHz switching PWM freq.
	
	//define SPI bus configuration
    bcm2835_spi_setBitOrder(BCM2835_SPI_BIT_ORDER_MSBFIRST);      // The default
    bcm2835_spi_setDataMode(BCM2835_SPI_MODE0);                   // The default
    bcm2835_spi_setClockDivider(BCM2835_SPI_CLOCK_DIVIDER_64); 	  // 4MHz clock with _64 
    bcm2835_spi_chipSelect(BCM2835_SPI_CS0);                      // The default
    bcm2835_spi_setChipSelectPolarity(BCM2835_SPI_CS0, LOW);      // the default

   	uint8_t mosi[10] = { 0x01, 0x00, 0x00 }; //12 bit ADC read 0x08 ch0, - 0c for ch1 
	uint8_t miso[10] = { 0 };
	
    //Define GPIO pins configuration
    bcm2835_gpio_fsel(PUSH1, BCM2835_GPIO_FSEL_INPT); 			//PUSH1 button as input
	bcm2835_gpio_fsel(PUSH2, BCM2835_GPIO_FSEL_INPT); 			//PUSH2 button as input
	bcm2835_gpio_fsel(TOGGLE_SWITCH, BCM2835_GPIO_FSEL_INPT);	//TOGGLE_SWITCH as input
	bcm2835_gpio_fsel(FOOT_SWITCH, BCM2835_GPIO_FSEL_INPT); 	//FOOT_SWITCH as input
	bcm2835_gpio_fsel(LED, BCM2835_GPIO_FSEL_OUTP);				//LED as output
	
    bcm2835_gpio_set_pud(PUSH1, BCM2835_GPIO_PUD_UP);           //PUSH1 pull-up enabled   
	bcm2835_gpio_set_pud(PUSH2, BCM2835_GPIO_PUD_UP);           //PUSH2 pull-up enabled 
	bcm2835_gpio_set_pud(TOGGLE_SWITCH, BCM2835_GPIO_PUD_UP);   //TOGGLE_SWITCH pull-up enabled 
	bcm2835_gpio_set_pud(FOOT_SWITCH, BCM2835_GPIO_PUD_UP);     //FOOT_SWITCH pull-up enabled 
	
	while(1) //Main Loop
	{
	//read 12 bits ADC
    bcm2835_spi_transfernb(mosi, miso, 3);
    input_signal = miso[2] + ((miso[1] & 0x0F) << 8); 

	//Read the PUSH buttons every 50000 times (0.25s) to save resources.
	read_timer++;
	if (read_timer==50000)
	{
	read_timer=0;
	uint8_t PUSH1_val = bcm2835_gpio_lev(PUSH1);
	uint8_t PUSH2_val = bcm2835_gpio_lev(PUSH2);
    TOGGLE_SWITCH_val = bcm2835_gpio_lev(TOGGLE_SWITCH);
	uint8_t FOOT_SWITCH_val = bcm2835_gpio_lev(FOOT_SWITCH);
	//light the effect when the footswitch is activated.
	bcm2835_gpio_write(LED,!FOOT_SWITCH_val); 
	
	//update booster_value when the PUSH1 or 2 buttons are pushed.
	if (PUSH1_val==0) //less distortion
		{ bcm2835_delay(100); //100ms delay for buttons debouncing
         if (distortion_value<2047) distortion_value=distortion_value+10;
		}
		else if (PUSH2_val==0) //more distortion
			{bcm2835_delay(100); //100ms delay for buttons debouncing.
			if (distortion_value>0) distortion_value=distortion_value-10;
			}
	}

	//**** FUZZ EFFECT ***///
	//The input_signal is clipped to the maximum value when it reaches the distortion_value threshold.
	//The guitar signal fluctuates above and under 2047.
    if (input_signal > 2047 + distortion_value) input_signal= 2047 + distortion_value;
	if (input_signal < 2047 - distortion_value) input_signal= 2047 - distortion_value;
	
	//generate output PWM signal 6 bits
    bcm2835_pwm_set_data(1,input_signal & 0x3F);
    bcm2835_pwm_set_data(0,input_signal >> 6);
    }
	
	//close all and exit
	bcm2835_spi_end();
    bcm2835_close();
    return 0;
}