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Teensy / Arduino eurorack sequencer

Drum / voltage sequencer

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  • Tested outputting to lots of LEDs via shift registers

    Lee Sampson6 days ago 2 comments

    I wanted to figure out the best way to run many LEDs quickly without using loads of IO pins. Here I tested using shift registers. I tried two methods, shiftOut() and SPI. I ran a test setting 16bits and recorded the time. Results:

    - shiftOut() = 204 μs

    - SPI = 16 μs

    Clearly SPI is much faster. Below are both methods.

    SPI Schematic:

    SPI test code:

    #include <SPI.h>
    
    //int pll_d=11; //piedino data
    //int pll_c=13; //piedino clock
    int pll_l=10; //piedino latch
    #define DATAOUT 11//MOSI
    #define DATAIN 12//MISO
    #define SPICLOCK 13//SCK
    
    int timer = 0;
    
    uint16_t ledNumbers[17] = { 0b0000000000000000, 
                                0b1000000000000000,
                                0b0100000000000000,
                                0b0010000000000000,
                                0b0001000000000000,
                                0b0000100000000000,
                                0b0000010000000000,
                                0b0000001000000000,
                                0b0000000100000000,
                                0b0000000010000000,
                                0b0000000001000000,
                                0b0000000000100000,
                                0b0000000000010000,
                                0b0000000000001000,
                                0b0000000000000100,
                                0b0000000000000010,
                                0b0000000000000001};
    
    
    void setup () {
    
      pinMode(DATAOUT, OUTPUT);
      pinMode(DATAIN, INPUT);
      pinMode(SPICLOCK,OUTPUT);
      pinMode(pll_l, OUTPUT);
    
      SPI.begin();
      Serial.begin(9600);
      SPI.setDataMode(SPI_MODE0);
      SPI.setBitOrder(LSBFIRST);
      SPI.setClockDivider(SPI_CLOCK_DIV2);
    
    
      timer = micros();
    
      digitalWrite(pll_l,LOW);
      SPI.transfer(ledNumbers[0]);
      SPI.transfer(ledNumbers[0] >> 8);
      digitalWrite(pll_l,HIGH);
      
      timer = micros() - timer;
      Serial.println(timer);
    
    }
    
    void loop() {
      // put your main code here, to run repeatedly:
    
      for(int x = 0; x < 16; x++){
        turnOn(ledNumbers[x + 1]);
        delay(500);
      }
      
    }
    
    void turnOn(uint16_t bitNum){
    
      digitalWrite(pll_l,LOW);
      SPI.transfer(bitNum);
      SPI.transfer(bitNum >> 8);
      digitalWrite(pll_l,HIGH);
    
    }
    


    shiftOut() Schematic:

    shiftOut() Code:

    int DS_pin = 11;
    int STCP_pin = 12;
    int SHCP_pin = 8;
    
    uint16_t ledOutput = 0;
    
    uint16_t ledNumbers[17] = { 0b0000000000000000, 
                                0b1000000000000000,
                                0b0100000000000000,
                                0b0010000000000000,
                                0b0001000000000000,
                                0b0000100000000000,
                                0b0000010000000000,
                                0b0000001000000000,
                                0b0000000100000000,
                                0b0000000010000000,
                                0b0000000001000000,
                                0b0000000000100000,
                                0b0000000000010000,
                                0b0000000000001000,
                                0b0000000000000100,
                                0b0000000000000010,
                                0b0000000000000001};
                          
    
    void setup()
    {
      Serial.begin(115200);
    
      pinMode(DS_pin,OUTPUT);
      pinMode(STCP_pin,OUTPUT);
      pinMode(SHCP_pin,OUTPUT);
    
      turnOn(4);
      delay(500);
      turnOn(8);
      delay(500);
      turnOn(12);
      delay(500);
      turnOn(16);
      delay(500);
    
      turnOff(4);
      delay(500);
      turnOff(8);
      delay(500);
      turnOff(12);
      delay(500);
      turnOff(16);
    }
    
    void loop()
    {
    
    
    }
    
    void turnOn(int bitNum)
    {
      ledOutput |= ledNumbers[bitNum];
      digitalWrite(SHCP_pin, LOW);
      shiftOut(DS_pin, STCP_pin, LSBFIRST, ledOutput); 
      shiftOut(DS_pin, STCP_pin, LSBFIRST, ledOutput  >> 8);
      digitalWrite(SHCP_pin, HIGH);
    }
    
    void turnOff(int bitNum)
    {
      ledOutput &= ~ledNumbers[bitNum];
      digitalWrite(SHCP_pin, LOW);
      shiftOut(DS_pin, STCP_pin, LSBFIRST, ledOutput); 
      shiftOut(DS_pin, STCP_pin, LSBFIRST, ledOutput  >> 8);
      digitalWrite(SHCP_pin, HIGH);
    }
    

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