SD Card and 74HC595

In my previous blog, I explained usage of Shift register using Node MCU and shown how to extend the additional digital input and output pins using 74HC595 and CD4021B shift register. In this blog we will use 74HC595 along with SD card and Node MCU.

74HC595: This is serial to parallel shift out register. You can use 8 digital output.This works in synchronous serial communication.

SD Card: SD Card will be used to store the data.

SD Card and 74HC595 Schematic

PIN Connections:

SD Card	Node MCU	74HC595N
MISO	D6 (GPIO12)
SCK	D5 (GPIO14)	SCK/SRCLK/SH_CP (PIN: 11) CLOCK PIN
	D3 (GPIO0)	RCK/SH_CP/RCKL (PIN: 12) LATCH
MOSI	D7 (GPIO13)	SER/DS (PIN: 14) DATA
CS/SS	D8 (GPIO15)
GND	GND	G/OE
	VCC (3.3V)	SCL/MR/SRCLR
VCC	VU (5V)

Once connection is made, you can use Arduino IDE to program the device. First thing is to initialise the Output pins as below,

pinMode(LATCHOUT_PIN, OUTPUT);

pinMode(CLOCK_PIN, OUTPUT);

SD Card Initialisation can be done as below,

pinMode(CHIPSELECT_PIN, OUTPUT);

// see if the card is present and can be initialized:

if (!SD.begin(CHIPSELECT_PIN)) {

// don't do anything more:

Serial.println("Card failed, or not present");

return false;

} else {

if (!isBaseDirAvailable()) {

createDirectory();

}

return true;

}

Serial.println("card initialized.");

Once initialisation is complete, then call the write and read method of the SD card to read or write on SD card device. Also in parallel you can set the digital output pin as per requirement.

Reading the file:

File readFile = SD.open(ROOT_DIRECTORY);

readFile.rewindDirectory();

dataReader(readFile, 0);

readFile.flush();

readFile.close();

Here if you are reading the files in loop then make sure that you rewind directory.

Writing the file:

if (!checkSpace(MINIMUM_SDCARD_SIZE)) {

deleteFile();

}

//SdFile::dateTimeCallback(TimeRecorder::dateTime);

File dataFile = SD.open(filename, FILE_WRITE);

uint32_t fileSize = dataFile.size();

fileSize /= 1024;

// if the file is available, write to it:

if (dataFile) {

dataFile.println(output);

// print to the serial port too:

//Serial.println(output);

} else {

Serial.println("Error in reading/opening file " + filename);

//dataFile.clearWriteError();

//Serial.print("Write Error: ");

}

dataFile.flush();

dataFile.close();

In above code before writting multiple files, we are checking the space. Also, if you are using Real Time Clock then you may want current timestamp while writting the file. This can be acheived as below,

SdFile::dateTimeCallback(TimeRecorder::dateTime); //TimeRecorder is your RTC setup class

dateTime callback method can be as below,

static void dateTime(uint16_t* date, uint16_t* time) {

static RTC_DS1307 RTCCall;

DateTime now = RTCCall.now();

// return date using FAT_DATE macro to format fields

*date = FAT_DATE(now.year(), now.month(), now.day());

// return time using FAT_TIME macro to format fields

*time = FAT_TIME(now.hour(), now.minute(), now.second());

}

Please find complete program as below,

Shift Registers (CD4021/74HC595) for increasing digital input and output pins

Arduino or Node MCU has limited digital pins and if you are using multiple sensors then there is chance that you may exaughst out of the digital input/output pins. In order to solve this issue, thank god we have Shift Registers. These shift registers can be used to increase the number of digital input and output pins. In this blog I will show you two shift registers which are used to increase digital input and output pins.

CD4021: This is parallel to serial shift in register. Using this shift register you can use upto 8 digital input. Also, this collects the input information asynchronously and all at once. You can call it Input Shift Register. Basically you can connect different digital inputs and collect the information.

74HC595: This is serial to parallel shift out register. You can use 8 digital output.This works in synchronous serial communication.

Schematic for 74HC595, CD4021BE and Node MCU

PIN Description is as below,

CD4021	Node MCU	74HC595N
Parallel Serial Controller (P/SC) (PIN: 9)	D1 (GPIO5)
CLOCK (PIN: 10) Clock PIN	D5 (GPIO14)	SCK/SRCLK/SH_CP (PIN: 11) CLOCK PIN
Q8 (PIN: 2)	D2 (GPIO4)
	D3 (GPIO0)	RCK/SH_CP/RCKL (PIN: 12) LATCH
	D7 (GPIO13)	SER/DS (PIN: 14) DATA
GND	GND	G/OE
VCC	VCC	SCL/MR/SRCLR

Once connection is made, you can use Arduino IDE to program the device. First thing is to initialise the Input/Output pins as below,

pinMode(LATCHOUT_PIN, OUTPUT);

pinMode(LATCHIN_PIN, OUTPUT);

pinMode(CLOCK_PIN, OUTPUT);

dataIn = 0;

dataIn = This is variable which stores the out values. For exampple, out of 8 output pin, you can set any bit and send signal to output shift registers.

Once Initialization is complete, then next step is to record Input/output values.

Set the output to 74HC595 output pins as below,

digitalWrite(CLOCK_PIN, LOW);

digitalWrite(LATCHOUT_PIN, LOW);

shiftOut(DATAOUT_PIN, CLOCK_PIN, variableData);

digitalWrite(LATCHOUT_PIN, HIGH);

Intial data out value is set as below,

byte dataOut = 0xFF;

Change the bit as per requirement and set theDigital pin out value.

Below code value is used to read the value from Input Shift Register.

digitalWrite(CLOCK_PIN, HIGH);

digitalWrite(LATCHIN_PIN, HIGH);

delayMicroseconds(5);

digitalWrite(LATCHIN_PIN, LOW);

dataIn = shiftIn(DATAIN_PIN, CLOCK_PIN);

Both Shift IN and Shift out functions are standard provided at link,

https://www.arduino.cc/en/Tutorial/ShiftOut

https://www.arduino.cc/en/Tutorial/ShiftIn

Please find complete program as below,