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TOPIC: Delay Guitar Effect Pedal.

Delay Guitar Effect Pedal. 5 years 9 months ago #870

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The delay effect with Raspberry Pi Zero is not limited by the amount of RAM memory (something that happens with Arduino). With 512MB of ram, we can store more than 16 millions of 32bits variables. Sampling at 44Ksps (CD quality) the maximum delay is around 381 seconds. Looks enough to me.

Part of the memory is used for the operating systems and other tasks, but in fact you can have a massive delay without problems.

This effect is based on a delay effect created for Arduino some time ago, the concept is the same: a circular buffer. Have a look here for more information.

How to control it:
  • Push-Button 1 (left): decrease the delay time.
  • Push-Button 2 (right): increase the delay time.
  • Led: ON when the effect is activated
  • Toggle Button: not used.
  • Foot-Switch: activate/deactivate the effect.

// CC-by-www.Electrosmash.com open-source project.
#include <stdio.h>
#include <bcm2835.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

//Define Delay Effect parameters MAX_DELAY 800000 is 4 seconds approx.
#define DELAY_MAX 800000
#define DELAY_MIN 0

uint32_t Delay_Buffer[DELAY_MAX];
uint32_t DelayCounter = 0;
uint32_t Delay_Depth = 100000; //default starting delay is 100000 is 0.5 sec approx.
uint32_t input_signal=0;
uint32_t output_signal=0;
uint32_t read_timer, delay;
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 
	//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.
	if (read_timer==50000)
	PUSH1_val = bcm2835_gpio_lev(PUSH1);
	PUSH2_val = bcm2835_gpio_lev(PUSH2);
    TOGGLE_SWITCH_val = bcm2835_gpio_lev(TOGGLE_SWITCH);
	FOOT_SWITCH_val = bcm2835_gpio_lev(FOOT_SWITCH);
	//light the effect when the footswitch is activated.
	//update volume variable when the PUSH buttons are pushed.
	if (PUSH2_val==0)
		{   bcm2835_delay(100); //100ms delay for buttons debouncing. 
			if (Delay_Depth<DELAY_MAX)Delay_Depth=Delay_Depth+50000; //50000 is 250ms approx.
           if (PUSH1_val==0) 
			    bcm2835_delay(100); //100ms delay for buttons debouncing. 
				if (Delay_Depth>DELAY_MIN)Delay_Depth=Delay_Depth-50000;
	//**** DELAY EFFECT ***///
	//The input_signal is saved in a "circular" buffer (Delay_Buffer) to be recovered later. 
	//The delayed signal is added again to the current guitar input so you can hear the original and delayed at the 
	//same time
	//With PUSH1 and PUSH2 the delay time is controlled.	
	Delay_Buffer[DelayCounter] = input_signal;
	if(DelayCounter >= Delay_Depth) DelayCounter = 0; 
	output_signal = (Delay_Buffer[DelayCounter]+input_signal)>>1;
    //generate output PWM signal 6 bits
    bcm2835_pwm_set_data(1,output_signal & 0x3F);
    bcm2835_pwm_set_data(0,output_signal >> 6);
 	//close all and exit
    return 0;

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Last Edit: 5 years 8 months ago by ES_Team.
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