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TOPIC: Clean-Transparent Guitar Pedal

Clean-Transparent Guitar Pedal 6 months 1 week ago #864

The code below is the simplest code you can start with to understand the process of "reading" and writing "audio".
The guitar signal is read using the MCP3202 ADC (SPI communication) and then is played back again using a dual PWM signal (PWM0 and PWM1 pins).
// CC-by-www.Electrosmash.com open-source project
// clean.c effect pedal, the signal is read by the ADC and written again using 2 PWM signals. 
 
#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;
 
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);
	bcm2835_gpio_write(LED,!FOOT_SWITCH_val); //light the effect when the footswitch is activated.
	}
 
	//**** CLEAN EFFECT ***///
	//Nothing to do, the input_signal goes directly to the PWM output.
 
	//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;
}
 


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File Name: clean.zip
File Size: 1 KB
Last Edit: 5 months 5 days ago by ElectroSmash_Team.
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