Temperature data logger using PIC18F46K22, SD card and DS18B20

This project shows how to build a temperature data logger using PIC18F46K22 microcontroller, SD card and DS18B20 digital temperature sensor.
The PIC18F46K22 MCU reads temperature values from the DS18B20 sensor and saves them to a text file stored in the SD card. DS1307 real time clock chip is used to get time and date information.
Time, date and temperature values are displayed on 20×4 LCD screen.
MikroC PRO for PIC compiler is used in this project.

FAT32 Library for mikroC compiler:
MikroElektronika provides a nice library for FAT32 file system (& SD card). This library can be downloaded from the following link:
FAT32 Library for mikroC compiler

The extension of the downloaded file is .mpkg, and in order to open and install the library we need a small software named: Package Manager, it’s also a free software provided by MikroElektronika, download link is below:
Package Manager download

To see how to interface PIC18F46K22 with SD card, visit the following post:
PIC18F46K22 Interface with SD card – Write & read files | mikroC Projects

Hardware Required:
This is a list of all components required to build this project.

  • PIC18F46K22 microcontroller   —->  datasheet
  • FAT32 formatted SD card (MMC, SD, SDHC, microSD ….)
  • micro SD card module
  • USB-to-serial UART converter (like: FT232RL module)
  • 20×4 LCD screen
  • DS18B20 temperature sensor    —->   datasheet
  • DS1307 RTC    —->    datasheet
  • 32.768 kHz crystal oscillator
  • 2 x 10k ohm resistor
  • 4.7k ohm resistor
  • 330 ohm resistor
  • 2 x push button
  • 10k ohm variable resistor or potentiometer
  • 3V coin cell battery
  • Breadboard
  • 5V source
  • Jumper wires

Temperature data logger using PIC18F46K22 circuit:
The following image shows project hardware circuit diagram.

As a small hint, it’s highly recommended to add a voltage level translator to MISO line in order to step up the 3.3V that comes from the SD card into 5V which goes to SDI1 pin (#23) of the PIC18F46K22 microcontroller, here we can use the integrated circuit 74HCT125.

In this project I used micro SD card module, this module is supplied from circuit 5V source, it contains the AMS1117-3V3 voltage regulator which is used to supply the SD card with 3.3V. Also this module contains an IC which is 74LVC125A and it is used as level translator (from 5V to 3.3V).

PIC18F46K22 DS18B20 data logger with SD card and DS1307 RTC

All the grounded terminals are connected together.

The PIC18F46K22 microcontroller does have 2 MSSP modules: MSSP1 and MSSP2 (MSSP: Master Synchronous Serial Port), each one of them may work as hardware SPI module or hardware I2C module. The SD card uses SPI protocol, it’s connected to MSSP1 module (used as SPI) hardware pins (SCK1, SDI1 and SDO1). So the micro SD card module is connected to the circuit as follows (from left to right):

The first pin of the micro SD card module (GND) is connected to circuit ground.
The second pin of the micro SD card module (VCC) is connected to circuit +5V.
The third pin of the micro SD card module (MISO) is connected to pin SDI1 (RC4) of the PIC18F46K22.
The fourth pin of the micro SD card module (MOSI) is connected to pin SDO1 (RC5) of the PIC18F46K22.
The fifth pin of the micro SD card module (SCK) is connected to pin SCK1 (RC3) of the PIC18F46K22.
The last pin of the micro SD card module (CS) is connected to pin RC2 of the PIC18F46K22.

The DS1307 RTC chip uses I2C protocol, its data pins (SCL and SDA) are connected to MSSP2 module which is configured to operate in I2C mode. So, the SCL and SDA pins of the DS1307 RTC are respectively connected to SCL2 (RD0) and SDA2 (RD1) of the PIC18F46K22 microcontroller.

In the circuit there are two push buttons: B1 and B2, they are connected to pins RB0 (#33) and RB1 (#34) respectively, these buttons are used to set time and date of the real time clock.

The DS18B20 temperature sensor has 3 pins (from left to right): GND, data and VCC where:
GND is connected to circuit ground (0V)
Data pin is connected to pin RB5 (#38) of the PIC18F46K22
VCC is connected to +5V.

The 20×4 LCD screen (4 rows and 20 columns) is used to display time, date and temperature where:
RS —> pin RD2
E   —> pin RD3
D4 —> pin RD4
D5 —> pin RD5
D6 —> pin RD6
D7 —> pin RD7
VSS, RW, D0, D1, D2, D3 and K are connected to circuit ground
VEE to the variable resistor (or potentiometer) output
VDD to +5V and A to +5V through 330 ohm resistor.

VEE pin is used to control the contrast of the LCD. A (anode) and K (cathode) are the back light LED pins.

The FT232RL board (USB to serial converter) RX pin is connected to PIC18F46K22 TX1 pin (RC6) which is USART1 module transmission pin (the PIC18F46K22 has 2 hardware USART modules).

In this project the PIC18F46K22 microcontroller runs with its internal oscillator @ 16 MHz and MCLR pin is configured as input.

Temperature data logger using PIC18F46K22 C code:
The C code below is for mikroC PRO for PIC compiler, it was tested with version 7.2.0.

To be able to compile project C code with no error, a driver (library) for the DS1307 RTC is required, download link is below. After you download the driver file which named DS1307.c, add it to your project folder.
DS1307 mikroC library

For more details about the DS1307 library, visit the following post:
DS1307 RTC Library for mikroC Compiler | mikroC Projects

The SD card chip select pin (SS) is connected to pin RC2 of the PIC18F46K22, it’s defined in the C code as:

The connection of the two push buttons are defined in the code as shown below:

The microcontroller reads temperature values from the DS18B20 sensor and saves it (with time and date) to the SD card every 10 seconds, for that I used the following if condition:

where the variable p_second is used to save only one value every 10 seconds.

Functions used in the code:
FAT32_Init(): this function initializes the FAT32 library as well as the SD card, it returns 0 if OK and non-zero if error.

FAT32_Open(“DS18B20Log.txt”, FILE_APPEND): this function creates (& opens) a new file named “DS18B20Log.txt” if it doesn’t already exists, if the file exists, it opens and moves the cursor to the end of the file, returns 0 if OK and non-zero if error (for example file exists).

FAT32_Write(fileHandle, “…”, 26): writes a text (for example “…” ) of length (for example 26 characters) to the file associated with fileHandler.

FAT32_Close(fileHandle): closes the file associated with fileHandler, returns 0 if OK and non-zero if error.

char debounce (): this function is for button B1 debounce, returns 1 if button is debounced.

void wait(): this function is just a delay of 500 ms except that it can be interrupted by the two push buttons (B1 and B2). In this function Timer0 module is used to count the 500 milliseconds, it is used as 16-bit timer with prescaler = 32 (==> 1 tick every 8 microseconds ==> 62500 x 8 = 500000 us = 500 ms).

char edit(char x_pos, char y_pos, char parameter): this function is for setting the real time clock, returns the edited parameter.

void dow_print(): displays day of the week (Monday, Tuesday …) on the LCD.

void rtc_print(): displays time and date on the LCD. This function calls the previous one for displaying day of the week.

unsigned int ds18b20_read(): this function reads temperature from the DS18B20 sensor, returns the value of the temperature as unsigned 16-bit number.

Rest of code is described through comments.

Full mikroC code:
Configuration words (for PIC18F46K22 MCU):
CONFIG1H = 0x0028
CONFIG2L = 0x0018
CONFIG2H = 0x003C
CONFIG3H = 0x0037
CONFIG4L = 0x0081
CONFIG5L = 0x000F
CONFIG5H = 0x00C0
CONFIG6L = 0x000F
CONFIG6H = 0x00E0
CONFIG7L = 0x000F
CONFIG7H = 0x0040

This project was tested in real hardware circuit using original Samsung microSD card with capacity of 32GB. The following image shows data logger file (DS18B20Log.txt) created by the hardware circuit:

DS18B20 data logger SD card file

Proteus simulation:
This project could be simulated using Proteus software, the following video shows the result of the simulation.
Note that Proteus simulation circuit is not the same as real hardware circuit, project hardware circuit is shown above.

Proteus simulation file download link:
PIC18F46k22 SD card DS1307 DS18B20 datalogger

SD Card image file (FAT32_MBR.ima) download link:
SD Card FAT32 image

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