Arduino•15h ago

Need help optimizing 74hc595 updates

Hi i need a way to make my 595 update faster currently it takes about 750 to 850 ms for 8bytes (8bits per iteration) to transfer using shiftout neeh help with to either make shiftout faster or update 595 over spi

23 Replies

Onigiri_CloudOP•15h ago

board: pro micro with atmega32u4

AnonEngineering•15h ago

might be a code issue, Googling indicates shiftOut takes about 150 us (on a ~~much slower~~ Uno)

Onigiri_CloudOP•15h ago

i am assuming u talking about per byte i am doing this 8 times per loop so it gets little high like 8 times that

AnonEngineering•15h ago

8 x 150 us is still only about a millisecond

Onigiri_CloudOP•15h ago

well i still require it being faster the delay of that adds up with other things making it like 3 miliseconds which is lot! and shift out adds the most of it to whole runtime

AnonEngineering•15h ago

800 seemed long, 3 ms I can picture 🙂

Onigiri_CloudOP•15h ago

so.... any idea how to make it faster?

AnonEngineering•15h ago

apparently folks have gained some speed driving the 595 with SPI, I haven't ever done it myself

Onigiri_CloudOP•15h ago

that seemed to be the most obvious answer but it's not working 595 output pins act kinda when i do spi and i am not sure if am doing it right or some bug? cause work fine with shiftout

#include <SPI.h>

const int latchPin = 14; 

void setup() {
  pinMode(latchPin, OUTPUT);
  digitalWrite(latchPin, LOW);

  SPI.begin();
}

void loop() {

  sendToShiftRegister(0b10101010); 
  delay(500);
  sendToShiftRegister(0b01010101); 
  delay(500);
}

// Function to send one byte to the 74HC595 via SPI
void sendToShiftRegister(uint8_t data) {
  digitalWrite(latchPin, LOW); 
  SPI.transfer(data);         digitalWrite(latchPin, HIGH);
}

#include <SPI.h>

const int latchPin = 14; 

void setup() {
  pinMode(latchPin, OUTPUT);
  digitalWrite(latchPin, LOW);

  SPI.begin();
}

void loop() {

  sendToShiftRegister(0b10101010); 
  delay(500);
  sendToShiftRegister(0b01010101); 
  delay(500);
}

// Function to send one byte to the 74HC595 via SPI
void sendToShiftRegister(uint8_t data) {
  digitalWrite(latchPin, LOW); 
  SPI.transfer(data);         digitalWrite(latchPin, HIGH);
}

this is what i did

pseud0•15h ago

How did you connect each pin?

AnonEngineering•14h ago

something like this? https://wokwi.com/projects/441920157134367745

Onigiri_CloudOP•14h ago

VCC to vcc SER to arduino 16 as data OE to ground RCLK to 14 as latch SRCLK to 15 as clock SRCLR to VCC

pseud0•14h ago

And what about pins like master reset

AnonEngineering•14h ago

isn't that SRCLR?

pseud0•14h ago

oh right that's your serial clear. GND to GNd technically.

Onigiri_CloudOP•14h ago

it is the same wait going to try the same code again

AnonEngineering•14h ago

yeah, i just changed the latch pin

Onigiri_CloudOP•14h ago

i think... it got updated once or twice not sure... it's on 0b01010101

AnonEngineering•14h ago

in other words your real life circuit isn't like the sim?

Onigiri_CloudOP•14h ago

void loop() {

  sendToShiftRegister(0b10101010);
  Serial.println("0b10101010");
  delay(1000);
  sendToShiftRegister(0b01010101);
  Serial.println("0b01010101");
  delay(1000);
}

void loop() {

  sendToShiftRegister(0b10101010);
  Serial.println("0b10101010");
  delay(1000);
  sendToShiftRegister(0b01010101);
  Serial.println("0b01010101");
  delay(1000);
}

yea can say that too also installed the spark fun promicro board defination just to make sure it wasn't the cause of issue

AnonEngineering•14h ago

how about not using 14 for latch (it's MISO)

Onigiri_CloudOP•13h ago

it has pinMode(latchPin, OUTPUT); think that disables 14 as miso? but yea will try that wow that fixed it! so turns out... this not true thanks for all the help! so i might have lost my last digital io pin but spi works! didn't have any plans of using that as for now so.. guess its fine?

AnonEngineering•12h ago

so it was using MISO as latch that was slowing it down?

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