UART or SD Card based 8-Channel Data-logger with temperature log

Hi Friends,
        here is one more data-logger circuit, which will be useful for some who have not much ventured into the ADC for datalogging or RTC or i2c communication, etc. This one is based on ATmega32. It has 8-channel 10-bit ADC. Hence, providing us with 8-channels with 0 to 5V voltage level measurement. The circuit also has on-board RTC (based on DS1307) to log the data with time-stamp. Data is logged via UART or using microSD card. The circuit has 3-pin UART connector, which can be used to connect to PC/laptop using UART(TTL) to USB serial converter, commonly available in electronic markets (UART setting: 38400-1-N-1).
      Also, there is a thermometer IC, DS1621, which is connected via i2c (along with the RTC IC) and provides temperature measurement from -55 to +125 Deg. C. The temperature is also sent along with the voltages to the UART for logging.
     (The logging with microSD card is added later in this post).
    The circuit schematic is given in the following figure (pdf file can be downloaded from here):

     At power on, the current date and time are displayed on the first raw of LCD. The temperature and the logging ON/OF status is displayed on the second raw. A green LED is also turned ON as an additional status of the proper power-up of the microcontroller .
     The data measurement can be started anytime by pressing the 'SET' button (keep pressed till the red LED turns ON). The recording ON status is displayed on LCD as well as by the glowing red LED. During this recording, at a regular interval (as defined in the code), the microcontroller gets the temperature from DS1621, measures the 8 voltages connected to 8 of its screw-terminals, w.r.t GND on the 9th terminal (as shown in the schematic), and forms a string which includes line number, time (hh:mm:ss format), temperature and the 8 voltage values, in a comma separated format. This string is then sent to UART, which can be logged into a file or seen on a terminal program in the PC/laptop using the serial-to-usb converter.
     The operation is shown in the following screen-shot of the Proteus simulation (in the simulation, the temperature set in the IC and displayed by the LCD has difference of 1.5C, as the code applies the correction factors read from the IC to the temperature reading and then displays it, which represents the actual temperature):

     (Note: The Proteus simulation files are included in the source code folder download at the end of the post).
   
     The circuit in operation, with logging ON and OFF, is shown the following pics:

        The actual UART output captured on a terminal of the Atmel Studio during the logging ON,  is shown in the left side image, where temperature shown is 30.3 C, channel-2 was connected with +5V (VCC) and channel-7 was connected with the Li battery cell of the RTC. Rest of the channels were kept open at the screw-terminals.

      The RTC date and time can be changed using the three push-buttons, similar to the procedure shown in my previous post of the RTC based relay-control. The procedure is given here:








 

For setting RTC Date/Time:

1. Press 'SET' button and Power ON the circuit, keeping the button pressed while the circuit is starting.
2. "RTC Setting.." message will be displayed on the first row of the LCD.
3.  Release the 'SET' button "Date: XX" will be displayed on the second row of the LCD, where XX is the existing current date as per the RTC.
4.  Press 'UP' or 'DOWN' button to increase or decrease the Date. When desired date is displayed, press 'SET' button to store it
5. "Month: XX" message will be displayed, where XX is the current month as per the RTC
6. Press 'UP' or 'DOWN' button to increase or decrease the Month. When desired month is displayed, press 'SET' button to store it
7. "Year: XXXX" will be displayed, use 'UP'/ 'DOWN' buttons to change the year and then press 'SET' button to store the year value
8. Then "Hour: XX" will be displayed, set it as per the previous steps and also set next "Minutes: XX" similarly, and store using 'SET' button.
9. When the Minutes is set, "RTC Setting" mode is over and normal operation resumes, where the LCD will display Date and time in the first row and temperature and log:OFF status in the second row.

 

• Data-logging with SD card 

         (Updated: Sep 2021)

Above image shows the logging with microSD card. A commonly available microSD card module (mostly used with Arduino) is used here. Please note that this module interferes with programming of the board on AVRISP port (which is not a problem with Arduino as it uses the USB bootloader programming and not AVRISP), so it's necessary to remove the card while loading the code. You can find solutions/modules online to overcome this issue.

Following images show the generated .csv file in the SD card and also opened file in MS-Excel. The logging was done without any voltages connected to the ADC channels, so the voltages are 0, but the  temperature log can be seen along with the time stamp. You can view another log file here, where I've connected the 8 channels to 3V RTC battery and VCC (~5V) line one by one (cross-coupling of signal to nearby free channel is also logged there).

The file name format is: DDMMYYNN.CSV, where DDMMYY is the date of logging and NN is the file number. After power on, the file number is set to 00. Every time logging is started and then stopped, the file number increments, hence, new file is created. As file number is a 2 digit value, max 100 (00 to 99) log files can be created after power on in a day, after that it will send error message. I guess you may not need to do the logging ON and OFF more than 100 times a day (after single power ON), but if you do, the file name string can be tweaks as necessary.

After Power off and on, when datalogging is started, the code looks if the filename is already existing or not, if it is, it will change the log-file number (and hence, name) to next available number, and so on. So, always a new file is created whenever logging is started.

• SD card datalogging using FatFS library

I'm  also uploading here the data-logging project code with a more generic FatFs library, which has been highly standardized and is officially supported/included by many IDEs/ Development boards/ Platforms (like Arduino, mbed, STM32, Keil, etc..). I've just replaced my FAT32 (and SD routines) libraries with FatFs modules. This also has been tested and the project folder is included in the downloads (Sr.No.2).

The datalogging and RTC setting procedures are same for all the above options, as explained in the earlier paragraphs. Functionality or user operations are same, only internal library change is there. Data-logging option with only UART or only SD card or both can be selected by proper macro selection in the main.h file. 

Note: You can connect UART while operating if you need to see the status/error messages for any troubleshooting. Otherwise, UART is not necessary if logging is done in SD card.

The circuit hardware is not much complicated, can be assembled on a general purpose PCB also. I'm including here the Gerber files also, along with the other downloads, if it's required.

Downloads:

1. Source Code for SD/UART Logging (with FAT32 Lib) (Atmel Studio-7 project)
2. Source Code for SD/UART Logging (with FatFs Lib) (Atmel Studio-7 project)
3. Proteus Simulation for UART datalogging
   
4. EAGLE Schematic and Board files
5. Gerber Files

Datasheets: ATmega32,   DS1307,   DS1621

 

You may also check out my post here, where I started on SD cards, for more info/ further reading/ references.

Enjoy!!

Regards,

CC Dharmani

ccd@dharmanitech.com

microSD ATmega32 Data-Logger

Hi friends,

aim of this project is to present a way to store a large quantity of data into microSD card in files with FAT32 format. Here, ATmega32 is used for data collection and microSD interface. The data is received from in-build 8-channel ADC of ATmega32. One channel is used for reading temperature from LM35 sensor and remaining channels are used for simply reading voltages and storing them.

This project can be used to interface 8 different sensors with ADC of ATmega32, similar to the LM35 used here. The data is stored in CSV (comma separated values) format, which can be read using a PC/Laptop with Microsoft Excel or other compatible software. A snapshot of the excel file is given later in this post.

This project is an example of how to use the microSD FAT32 library presented in my earlier post. In that post, the files were created using hyper-terminal and entering data with the PC keyboard, since that demonstrates the file creation and it's easy to debug. But many users have requested to make the file creation independent of the terminal, done inside the microcontroller, so I'm showing here how to use those functions independent of terminal. If you have directly landed on this page, it would be more helpful if you visit the original post first as it would be a better starting place for learning SD or FAT32 functions (also Check out my this post for updated version of this project with 16x2 LCD and DS1621 temperature sensor

Here is the schematic (click on the images for larger view or download PDF):

The project contains RTC interface (for date and time storage), RS232 (for connection with PC) and a microSD module. Here, the hyper-terminal connection is required only for setting RTC date and time. Once the date/time are set, the RS232 connection is not required anymore for normal data-logging operation (It can be used for debugging purpose if there is a problem).

The microSD module used here is from eXtreme Electronics.
The module is shown in the figure here. Other than the microSD socket, this low-cost module also contains on-board 3.3v regulator for the microSD card, a 5v-3.3v level converter and other safety features required for the card. This module is used here as it provides a stable interface and makes the the card compatible with 5v supply and 5v signals of microcontroller.

The module is available at: http://store.extremeelectronics.co.in/MicroSD-TF-Module.html

The schematic also shows two LEDs and a push-button. The LEDs are used for indications of power and recording and the push-button is used to start-stop recording.

Operation of the circuit:
-----------------------------------------------
For setting RTC date/time (or for debugging mode):

• Connect the microSD module, insert the microSD card
• Connect the RS232 cable with the circuit. Set-up hyper terminal with 19200 baud, no parity, 8-bit data, 1 stop-bit and flow-control as 'None'
• Connect the power cable and power on the circuit while keeping the push-button pressed
• Green LED will glow in the circuit board
• A menu will be displayed on the Hyper terminal as shown in the figure below. Select desired option and follow the displayed instructions
• When date/time is set or debugging done, select option '0' to come out of the menu and start functioning a s data-logger
• At this point, the RS232 cable can be removed

Operation as Data-Logger:

• Connect the power cable and power on the circuit
• Green LED will glow
• Whenever the data-logging is required, press the push-button
• Red LED will glow, indicating that the recording has started
• To stop recording, press the push-button again, recording will stop and red LED will turn off
• Files stored in the card can be read using a PC card-reader or using hyper-terminal with the circuit started in debugging mode

The operation is very simple as it uses just one push-button and an LED indication. In case of any error in accessing the card, red LED will blink continuously. In such a case, you can start circuit in debug mode (with terminal) and see the error messages.

Files are stored with the date as a name and .CSV extension. For example, data-logging done on 10 May 2011 would be stored in "10052011.CSV" file. Since the date is the name of file, everyday a single file is created and all the data recording done in a day goes into single file, no matter how many times the recording is stopped/started. First column of the file shows date, second shows time and next 8 columns show data from the 8 channels.

A file created during testing is shown in the figure below, where 5 sec interval was set for measurements (click on the image to enlarge it). Here channel-0 was used for LM35 temperature sensor, and remaining channels measure voltage. 5v was connected to channel-1 and 3v Li cell was connected to channel-3 (Channel 2 & 4 show some small voltages due to noise from voltages connected to nearby channels, which can be corrected by using bypass caps).


The interval between two measurement cycles is defined in main.c file, which can be set as per the user requirement. Basically, the program forms a dataString in every measurement cycle and appends this string to the file, if the file already exists or it creates a new file (for example, during the first recording in a day). You may go through the comments in the source code file for more info.

Note: Make sure that RTC circuit is properly connected, otherwise the code will simply hang waiting for receiving date & time from RTC

New Version: Check out my this post for updated version of this project with 16x2 LCD and DS1621 temperature sensor. Project Code with FatFs library is also shared there.

Download project files
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The source code is written in AVR-GCC format using winAVR with AVRStudio-4, complete AVRStudio project folder can be downloaded from here:

- Download Source Code

Download schematic:
- Schematic (PDF)
- Schematic (EAGLE)

References:
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Visit my earlier post for the references on SD card & FAT32 which are given at the end of the post