DataLogger with PIC18F4550, SD card and DHT11 sensor

This post shows how to make a temperature and humidity datalogger using PIC18F4550 microcontroller, SD card and DHT11 sensor where the temperature and humidity measurements are saved in a text file (located on the SD card). The compiler used in this project is CCS PIC C.

In this project the PIC18F4550 reads relative humidity and temperature data from the DHT11 sensor and after creating a text file on the SD card named “1Log.txt”, it starts writing that data to the text file.
A 16×2 LCD screen is connected to the microcontroller in order to display the relative humidity and temperature measurements.

To be able to build this project we need MMC/SD card driver and FAT library for CCS C compiler, their download links are in the topic below (official post of the two libraries), the names of the two files (with the extension) respectively are: mmcsd_m.c and fat_m.c. After downloading just add the two files to the project folder or to CCS C drivers folder:
SD Card driver and FAT Library for CCS C compiler

Hardware Required:

PIC18F4550 microcontroller
FAT32 formatted SD card (MMC, SD, SDHC, micro SD ….)
DHT11 relative humidity and temperature sensor
microSD card module (adapter)
USB-to-serial UART module (optional)
16×2 LCD screen
8MHz crystal oscillator
2 x 22pF ceramic capacitors
4.7k ohm resistor
10k ohm variable resistor or potentiometer
Breadboard
5V source
Jumper wires

PIC18F4550 SD card data logger circuit:
PIC18F4550 datalogger circuit diagram is shown below.

In this project the microcontroller runs with an external crystal oscillator of 8MHz and MCLR pin is configured as a digital input pin (in the software).

The temperature and humidity measurements are displayed on the 16×2 LCD screen and stored on the microSD card. The microSD card is placed in the module (adapter).

The USB to serial UART module such as FT232RL is used to connect the microcontroller with the laptop (PC), in this example it shows the initialization status of the SD card and FAT system.

As a hint, instead of the microSD card module we can use AMS1117-3V3 to supply the SD card and three voltage dividers for SS, SCK and MOSI lines; each voltage divider consists of two resistors: 2.2k ohm and 3.3k ohm. Related project link above shows the circuit diagram.

PIC18F4550 SD card data logger C code:
The C code below is for CCS C compiler, it was tested with version 5.051.

As written above, to be able to compile the C code below, we need MMC/SD driver and FAT library (mmcsd_m.c and fat_m.c), their download links are in this page:
SD Card driver and FAT Library for CCS C compiler

The compilation of the project C code may give some warnings, just ignore them!

With the 8MHz and PLL2 the microcontroller becomes working at 48MHZ (12 MIPS) which is the highest speed of the PIC18F4550 and its hardware SPI module.

In this example I used software SPI just to show how the FAT library works with soft SPI mode. Hardware SPI is much faster the the soft one.

I used Timer1 module to measure pulse widths, with a prescaler of 8, Timer1 increments by 1.5 every 1us (15 every 10us).

Used functions:
void Start_Signal(void): sends the start signal to the DHT11 sensor.
int1 Check_Response(void): reads the response signal that comes from the DHT11 sensor, returns 1 if OK and zero if error.
int1 Read_Data(int8 *dht_data): reads humidity and temperature data from the DHT11 sensor and save data to pointer ‘dht_data‘, returns 0 if OK and 1 if error.
fat_init(): initializes the FAT system and the media card, returns 0 if OK and non-zero if there was an error.
mk_file: creates a new file on the SD card, returns 0 if OK, non-zero if error.
fatopen: opens a file, returns 0 if OK, non-zero if error.
fatputs: puts a string into the opened file, returns 0 if OK, non-zero if error.
fatclose: closes the opened file, after writing to the file we must call this function, returns 0 if OK, non-zero if there error.

Full CCS C code:

// Temperature and humidity data logger using PIC18F4550, SD card and DHT11 sensor
// C code for CCS C compiler
// http://simple-circuit.com/

// LCD module connections
#define LCD_RS_PIN      PIN_D0
#define LCD_RW_PIN      PIN_D1
#define LCD_ENABLE_PIN  PIN_D2
#define LCD_DATA4       PIN_D3
#define LCD_DATA5       PIN_D4
#define LCD_DATA6       PIN_D5
#define LCD_DATA7       PIN_D6
// End LCD module connections

// SD card module connections
#define MMCSD_PIN_SELECT  PIN_B0
#define MMCSD_PIN_SCK     PIN_B1
#define MMCSD_PIN_MOSI    PIN_B2
#define MMCSD_PIN_MISO    PIN_B3
// End SD card module connections

// DHT11 sensor connection
#define DHT11_PIN PIN_B4                              // DHT11 Data pin is connected to RB4
// End DHT11 sensor connection

#include <18F4550.h>
#device PASS_STRINGS = IN_RAM
#fuses NOMCLR HSPLL PLL2 CPUDIV1
#use delay(clock = 48MHz)
#use fast_io(B)
#use fast_io(D)
#use rs232 (baud=9600, xmit=PIN_C0, rcv=PIN_C1)     // Initialize UART protocol (needed for FAT library)
#include <lcd.c>                       // Include LCD driver source file
#include <mmcsd_m.c>                   // Include MMC/SD card driver source file
#include <fat_m.c>                     // Include FAT library source file


char temperature[] = "Temp = 00.0 C  ";
char humidity[]    = "RH   = 00.0 %  ";
int8 T_Byte1, T_Byte2, RH_Byte1, RH_Byte2, CheckSum ;
FILE MyLog;

void Start_Signal(void){
  output_drive(DHT11_PIN);                            // Configure connection pin as output
  output_low(DHT11_PIN);                              // Connection pin output low
  delay_ms(25);
  output_high(DHT11_PIN);                             // Connection pin output high
  delay_us(30);
  output_float(DHT11_PIN);                            // Configure connection pin as input
}
int1 Check_Response(void){
  set_timer1(0);                                      // Set Timer1 value to 0
  setup_timer_1(T1_INTERNAL | T1_DIV_BY_8);           // Start Timer1 with internal clock source + 8 prescaler
  while(!input(DHT11_PIN) && get_timer1() < 150);     // Wait until DHT11_PIN becomes high (cheking of 80µs low time response)
  if(get_timer1() > 149)                               // If response time > 99µS  ==> Response error
    return 0;                                         // Return 0 (Device has a problem with response)
  else {
    set_timer1(0);                                    // Set Timer1 value to 0
    while(input(DHT11_PIN) && get_timer1() < 150);    // Wait until DHT11_PIN becomes low (cheking of 80µs high time response)
    if(get_timer1() > 149)                            // If response time > 99µS  ==> Response error
      return 0;                                       // Return 0 (Device has a problem with response)
    else
      return 1;                                       // Return 1 (response OK)
  }
}

int1 Read_Data(int8 *dht_data) {
  int8 j;
  *dht_data = 0;
  for(j = 0; j < 8; j++){
    set_timer1(0);                                    // Reset Timer1
    while(!input(DHT11_PIN))                          // Wait until DHT11_PIN becomes high
      if(get_timer1() > 150) {                        // If low time > 100  ==>  Time out error (Normally it takes 50µs)
        return 1;
      }
    set_timer1(0);                                    // Reset Timer1
    while(input(DHT11_PIN))                           // Wait until DHT11_PIN becomes low
      if(get_timer1() > 150) {                        // If high time > 100  ==>  Time out error (Normally it takes 26-28µs for 0 and 70µs for 1)
        return 1;                                     // Return 1 (timeout error)
      }
     if(get_timer1() > 70)                            // If high time > 50  ==>  Sensor sent 1
       bit_set(*dht_data, (7 - j));                   // Set bit (7 - i)
  }

  return 0;                                           // Return 0 (data read OK)
}

void main(void) {
  char txt[4];
  int8 i;
  int16 line = 0;

  lcd_init();                                         // Initialize LCD module
  lcd_putc('\f');                                     // clear LCD command
  delay_ms(2000);                                     // wait 2 seconds

  // Initializing the FAT library as well as the SD card ---> returns 0 if OK
  printf("Initializing FAT library ... ");
  i = fat_init();
  
  if( i == 0) {          // initialization OK
    printf("OK");
    mk_file("/DHT11Log.txt");                         // Create a new file with name 'DHT11Log.txt'
    fatopen("/DHT11Log.txt", "w", &MyLog);            // Open 'DHT11Log.txt' with write permission 'w'
    fatputs("Temperature and humidity data logger using PIC18F4550 microcontroller and DHT11 sensor\r\n\r\n" , &MyLog);
    fatclose(&MyLog);
  }

  else                    // FAT initialization error
    printf("Error!");

  while(TRUE) {

    if( i == 0) {                                // If the FAT library was initialized with no error
      fatopen("/DHT11Log.txt", "a", &MyLog);     // Open 'DHT11Log.txt' with append permission 'a'
      sprintf(txt, "%03Lu", ++line);
      fatputs(txt, &MyLog);
      fatputs(":    Temperature = ", &MyLog);
    }

    Start_Signal();                              // Send start signal to the sensor

    if(Check_Response()) {                       // Check if there is a response from sensor (If OK start reding humidity and temperature data)

    // Read (and save) data from the DHT11 sensor and check time out errors
      if(Read_Data(&RH_Byte1) || Read_Data(&RH_Byte2) || Read_Data(&T_Byte1) || Read_Data(&T_Byte2) || Read_Data(&CheckSum)) {
        lcd_putc('\f');                               // clear LCD
        lcd_gotoxy(5, 1);                             // Go to column 5 row 1
        lcd_putc("Time out!");                        // Display "Time out!"
      }

      else {                                               // If there is no time out error
        if(CheckSum == ((RH_Byte1 + RH_Byte2 + T_Byte1 + T_Byte2) & 0xFF)) {
        // If there is no checksum error
          temperature[7]  = T_Byte1 / 10  + 48;
          temperature[8]  = T_Byte1 % 10  + 48;      // % is the modules operator
          temperature[10] = T_Byte2 / 10  + 48;
          humidity[7]     = RH_Byte1 / 10 + 48;
          humidity[8]     = RH_Byte1 % 10 + 48;
          humidity[10]    = RH_Byte2 / 10 + 48;
          temperature[11] = 223;                      // Put degree symbol (°)

          // Print data on the LCD
          lcd_gotoxy(1, 1);                           // Go to column 1 row 1
          printf(lcd_putc, temperature);              // Display temperature
          lcd_gotoxy(1, 2);                           // Go to column 1 row 2
          printf(lcd_putc, humidity);                 // Display humidity

          if( i == 0) {                               // If the FAT library was initialized with no error
            // Write data to SD card file (DHT11Log.txt)
            sprintf(txt, "%02u", T_Byte1);
            fatputs(txt, &MyLog);                       // write temperature
            fatputs("°C  |  Humidity = ", &MyLog);
            sprintf(txt, "%02u", RH_Byte1);
            fatputs(txt, &MyLog);                       // write humidity
            fatputs("%", &MyLog);
          }
        }
        // If there is checksum error
        else {
          lcd_putc('\f');                             // LCD clear
          lcd_gotoxy(1, 1);                           // Go to column 1 row 1
          lcd_putc("Checksum Error!");
        }
      }
    }

    // If there is response problem (from the sensor) 
    else {
      lcd_putc('\f');                                 // LCD clear
      lcd_gotoxy(3, 1);                               // Go to column 3 row 1
      lcd_putc("No response");
      lcd_gotoxy(1, 2);                               // Go to column 1 row 2
      lcd_putc("from the sensor");
    }

    if( i == 0) {                               // If the FAT library was initialized with no error
      fatputs("\r\n" , &MyLog);                           // Start new line
      fatclose(&MyLog);                                   // Close 'DHT11Log.txt' file
    }

    setup_timer_1(T1_DISABLED);                         // Disable Timer1 module
    delay_ms(1000);                                     // Wait 1 second

  }

}
// End of code

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// Temperature and humidity data logger using PIC18F4550, SD card and DHT11 sensor

// C code for CCS C compiler

// http://simple-circuit.com/

// LCD module connections

#define LCD_RS_PIN PIN_D0

#define LCD_RW_PIN PIN_D1

#define LCD_ENABLE_PIN PIN_D2

#define LCD_DATA4 PIN_D3

#define LCD_DATA5 PIN_D4

#define LCD_DATA6 PIN_D5

#define LCD_DATA7 PIN_D6

// End LCD module connections

// SD card module connections

#define MMCSD_PIN_SELECT PIN_B0

#define MMCSD_PIN_SCK PIN_B1

#define MMCSD_PIN_MOSI PIN_B2

#define MMCSD_PIN_MISO PIN_B3

// End SD card module connections

// DHT11 sensor connection

#define DHT11_PIN PIN_B4 // DHT11 Data pin is connected to RB4

// End DHT11 sensor connection

#include <18F4550.h>

#device PASS_STRINGS = IN_RAM

#fuses NOMCLR HSPLL PLL2 CPUDIV1

#use delay(clock = 48MHz)

#use fast_io(B)

#use fast_io(D)

#use rs232 (baud=9600, xmit=PIN_C0, rcv=PIN_C1) // Initialize UART protocol (needed for FAT library)

#include <lcd.c> // Include LCD driver source file

#include <mmcsd_m.c> // Include MMC/SD card driver source file

#include <fat_m.c> // Include FAT library source file

char temperature[] = "Temp = 00.0 C ";

char humidity[] = "RH = 00.0 % ";

int8 T_Byte1, T_Byte2, RH_Byte1, RH_Byte2, CheckSum ;

FILE MyLog;

void Start_Signal(void){

output_drive(DHT11_PIN); // Configure connection pin as output

output_low(DHT11_PIN); // Connection pin output low

delay_ms(25);

output_high(DHT11_PIN); // Connection pin output high

delay_us(30);

output_float(DHT11_PIN); // Configure connection pin as input

}

int1 Check_Response(void){

set_timer1(0); // Set Timer1 value to 0

setup_timer_1(T1_INTERNAL | T1_DIV_BY_8); // Start Timer1 with internal clock source + 8 prescaler

while(!input(DHT11_PIN) && get_timer1() < 150); // Wait until DHT11_PIN becomes high (cheking of 80µs low time response)

if(get_timer1() > 149) // If response time > 99µS ==> Response error

return 0; // Return 0 (Device has a problem with response)

else {

set_timer1(0); // Set Timer1 value to 0

while(input(DHT11_PIN) && get_timer1() < 150); // Wait until DHT11_PIN becomes low (cheking of 80µs high time response)

if(get_timer1() > 149) // If response time > 99µS ==> Response error

return 0; // Return 0 (Device has a problem with response)

else

return 1; // Return 1 (response OK)

}

int1 Read_Data(int8 *dht_data) {

int8 j;

*dht_data = 0;

for(j = 0; j < 8; j++){

set_timer1(0); // Reset Timer1

while(!input(DHT11_PIN)) // Wait until DHT11_PIN becomes high

if(get_timer1() > 150) { // If low time > 100 ==> Time out error (Normally it takes 50µs)

return 1;

}

set_timer1(0); // Reset Timer1

while(input(DHT11_PIN)) // Wait until DHT11_PIN becomes low

if(get_timer1() > 150) { // If high time > 100 ==> Time out error (Normally it takes 26-28µs for 0 and 70µs for 1)

return 1; // Return 1 (timeout error)

}

if(get_timer1() > 70) // If high time > 50 ==> Sensor sent 1

bit_set(*dht_data, (7 - j)); // Set bit (7 - i)

}

return 0; // Return 0 (data read OK)

}

void main(void) {

char txt[4];

int8 i;

int16 line = 0;

lcd_init(); // Initialize LCD module

lcd_putc('\f'); // clear LCD command

delay_ms(2000); // wait 2 seconds

// Initializing the FAT library as well as the SD card ---> returns 0 if OK

printf("Initializing FAT library ... ");

i = fat_init();

if( i == 0) { // initialization OK

printf("OK");

mk_file("/DHT11Log.txt"); // Create a new file with name 'DHT11Log.txt'

fatopen("/DHT11Log.txt", "w", &MyLog); // Open 'DHT11Log.txt' with write permission 'w'

fatputs("Temperature and humidity data logger using PIC18F4550 microcontroller and DHT11 sensor\r\n\r\n" , &MyLog);

fatclose(&MyLog);

}

else // FAT initialization error

printf("Error!");

while(TRUE) {

if( i == 0) { // If the FAT library was initialized with no error

fatopen("/DHT11Log.txt", "a", &MyLog); // Open 'DHT11Log.txt' with append permission 'a'

sprintf(txt, "%03Lu", ++line);

fatputs(txt, &MyLog);

fatputs(": Temperature = ", &MyLog);

}

Start_Signal(); // Send start signal to the sensor

if(Check_Response()) { // Check if there is a response from sensor (If OK start reding humidity and temperature data)

// Read (and save) data from the DHT11 sensor and check time out errors

if(Read_Data(&RH_Byte1) || Read_Data(&RH_Byte2) || Read_Data(&T_Byte1) || Read_Data(&T_Byte2) || Read_Data(&CheckSum)) {

lcd_putc('\f'); // clear LCD

lcd_gotoxy(5, 1); // Go to column 5 row 1

lcd_putc("Time out!"); // Display "Time out!"

}

else { // If there is no time out error

if(CheckSum == ((RH_Byte1 + RH_Byte2 + T_Byte1 + T_Byte2) & 0xFF)) {

// If there is no checksum error

temperature[7] = T_Byte1 / 10 + 48;

temperature[8] = T_Byte1 % 10 + 48; // % is the modules operator

temperature[10] = T_Byte2 / 10 + 48;

humidity[7] = RH_Byte1 / 10 + 48;

humidity[8] = RH_Byte1 % 10 + 48;

humidity[10] = RH_Byte2 / 10 + 48;

temperature[11] = 223; // Put degree symbol (°)

// Print data on the LCD

lcd_gotoxy(1, 1); // Go to column 1 row 1

printf(lcd_putc, temperature); // Display temperature

lcd_gotoxy(1, 2); // Go to column 1 row 2

printf(lcd_putc, humidity); // Display humidity

if( i == 0) { // If the FAT library was initialized with no error

// Write data to SD card file (DHT11Log.txt)

sprintf(txt, "%02u", T_Byte1);

fatputs(txt, &MyLog); // write temperature

fatputs("°C | Humidity = ", &MyLog);

sprintf(txt, "%02u", RH_Byte1);

fatputs(txt, &MyLog); // write humidity

fatputs("%", &MyLog);

}

// If there is checksum error

else {

lcd_putc('\f'); // LCD clear

lcd_gotoxy(1, 1); // Go to column 1 row 1

lcd_putc("Checksum Error!");

}

// If there is response problem (from the sensor)

else {

lcd_putc('\f'); // LCD clear

lcd_gotoxy(3, 1); // Go to column 3 row 1

lcd_putc("No response");

lcd_gotoxy(1, 2); // Go to column 1 row 2

lcd_putc("from the sensor");

}

if( i == 0) { // If the FAT library was initialized with no error

fatputs("\r\n" , &MyLog); // Start new line

fatclose(&MyLog); // Close 'DHT11Log.txt' file

}

setup_timer_1(T1_DISABLED); // Disable Timer1 module

delay_ms(1000); // Wait 1 second

}

// End of code

I tested this project with Samsung 8GB (SDHC) and 2GB (SDSC) microSD cards, both are formatted with FAT32 file system, I got the file shown below:

The following video shows Proteus simulation of the project, I got the same result as the hardware circuit. Note that the simulation circuit is not the same as the hardware circuit, the hardware circuit diagram is shown above.

Proteus simulation file download:
Download
SD card image file download:
Download

sumit

November 8, 2018 at 3:51 am

#fuses NOMCLR HSPLL PLL2 CPUDIV1—————working fine
//#fuses MCLR, HSPLL, PLL2, CPUDIV1 ——- MCLR NOT WORKING PLEASE TELL ME
#use delay(clock=48000000,crystal=8000000) —— working fine

I WANT MCLR PIN TO WORK AS MCLR PIN
IS FILE WITH MBR SUPPORT HAVE DIFFERENT DOWNLOAD LINK OR WE HAVE DOWNLOADED CORRECT FILE HOW TO CHECK IT

SIMULATION WORKING FINE BUT I WANT MCLR PIN TO WORK WITH THE SAME CODE

THANK YOU FOR YOUR SUPPORT

sumit
November 10, 2018 at 9:08 pm
I REQUEST AUTHOR TO REPLY, author contact details ????
Simple Projects
November 10, 2018 at 10:03 pm
If you wan to use the MCLR pin you’ve to add it’s circuit and the easiest one is by connecting the MCLR pin to VCC (+5V) through 10k ohm resistor.
Currently there is only one link for the FAT library which supports SD cards with or without MBR.

mariano

November 2, 2018 at 2:33 am

La nueva biblioteca FAT es la fat_m u otra?

Legend

October 11, 2018 at 1:07 am

Good work you have done. your tutorial is very detailed and easy to follow. Like Ismael, I tested your code with the same type of hardware you have used, it works well on Proteus but on hardware, it detects the FAT but when creating files or folders the pic is frozen, and you can never create files or folders on the SD card. any solution?

Simple Projects
October 15, 2018 at 1:54 pm
The FAT library has been updated to ‘support’ SD cards with MBR. Re-download it again and add it to your project!
You’re facing this error may be because your SD card has MBR, the updated library may work for you.
1. Legend
  October 17, 2018 at 10:11 am
  Thanks very much for your response, I downloaded the new FAT library that support SD card with MBR, and every thing worked well now. I am able to create directory and files. Please continue with the good work. see logged file below.
  Temperature and Humidity Logger created by Legened
  Temp= 27.0ßC RH = 37.0 %
  Temp= 27.0ßC RH = 41.0 %
  Temp= 26.0ßC RH = 41.0 %
  Temp= 27.0ßC RH = 40.0 %
  Temp= 26.0ßC RH = 41.0 %
  Temp= 26.0ßC RH = 40.0 %
  Temp= 26.0ßC RH = 40.0 %
  Temp= 27.0ßC RH = 39.0 %
  Temp= 26.0ßC RH = 40.0 %
  Temp= 26.0ßC RH = 40.0 %
  Temp= 26.0ßC RH = 40.0 %
  Temp= 26.0ßC RH = 40.0 %
  Temp= 26.0ßC RH = 40.0 %

DataLogger with PIC18F4550, SD card and DHT11 sensor

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