SD.h 和 U8x8.h (LCD) 之间的 SPI 冲突

Question

I want to reproduce a .wav file on my Arduino Uno via an SD card while at the same time using an LCD display (Nokia 5110). I'm having trouble trying to make the double SPIs work and since I'm not really familiar with the libraries that I used I decided to ask for help

The problem is that once the program execute SD.begin() the display stops working and the SPI communication is working only on the SD.

In this setup that I'm showing I will initialize the SD in the setup() and in the loop using a button I'm supposed to write stuff on the display:

//Libraries
  #include <U8x8lib.h>
  #include <SPI.h>
  #include "SD.h"
  #include "TMRpcm.h"

  //Display                         (pin 13,  pin 11,  pin A1, pin 12, pin A0 )
    U8X8_PCD8544_84X48_4W_SW_SPI lcd(LCD_CLK, LCD_DIN, LCD_CE, LCD_DC, LCD_RST); 

  //Speaker
    TMRpcm music;


void setup() {
  
  //Serial port -> Open
    Serial.begin(9600);
    while (!Serial) {}

  //LCD
    display_setup();
    display_somethingElse();

  //SD and Speaker
    sdAndSpeaker_setup();

}

void loop() {

  topButton.poll();
  if (topButton.buttonClicked) {
    display_something();  
  }
  
}

Ignore the function related to the button, I removed most of its code to avoid cluttering the page.

Here's when the problem occurs:

void sdAndSpeaker_setup() {

    music.speakerPin = 10;
//               (pin 4)
    if (!SD.begin(SD_CS)) {
    Serial.println("SD fail");
    Serial.flush();
    abort();
    }
    
    music.setVolume(4);
    music.play("Daybreak.wav");
    music.quality(2);
    
}

I know that by changing the pins of display to other value (rather than 11, 12 and 13) the problems is solved but most of the pins in my board are already used and I don't have this luxury... I think this has something to do with the U8x8.h and SD.h library but I don't have the skills to tweak those.

If anyone has a suggestion I'll appreciate! Thanks!

Answer 1

The constructor

 U8X8_PCD8544_84X48_4W_SW_SPI(uint8_t clock, uint8_t data, uint8_t cs, uint8_t dc, uint8_t reset = U8X8_PIN_NONE)

creates a 'driver' which uses software SPI. But you supply pins of hardware SPI as parameters. Hardware SPI is used by the SD library over the SPI library to access the SD card, so hardware SPI conflicts with the software SPI of the display library .

There is a

U8X8_PCD8544_84X48_4W_HW_SPI(uint8_t cs, uint8_t dc, uint8_t reset = U8X8_PIN_NONE)

constructor which uses the hardware SPI over the SPI library. The SPI library 'knows' the pin numbers of the SPI pins. (SPI library is part of the boards package. It can't be installed separately.)

If you want to use the software SPI, use free pins. The hardware SPI uses pins 11, 12, 13 on Uno.