Wednesday, July 4, 2018

UART 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. 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.
      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.
(Note: The circuit also has the microSD card module connector, for logging the data into the card in FAT32 file format, instead of sending it to UART, but that part is not used here, as this initial part is more intended for new learners. Part-2 with microSD will be included shortly in the next update. Meanwhile, you may refer to my earlier post on microSD related posts, here and here, for getting some details and code for SD card/ FAT32 format).

    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.
     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.


1. Source Code project files with Simulation files (Atmel Studio-7 and Proteus formats)

Datasheets: ATmega32,   DS1307,   DS1621



CC Dharmani

Saturday, June 23, 2018

Relay-Timer Circuit with RTC (for auto-operating appliances)

Hi friends,
     it's been years since I put up a new post here. So, starting again with a simple circuit, based on ATmega8, might be useful for newbies in AVR, RTC, Relay, etc.This is RTC based relay operating circuit to automatically power ON/OFF any electrical device/appliance at a preset time. 
    The necessity behind it was this: I had started taking a 230V AC electrical Tiffin (lunch) box to office a few months back, which takes minimum 30 minutes to very slowly heat up the food (it's kept slow heating as the idea is to just heat the food without re-cooking it). That means it's necessary to turn the box ON 30 minutes before lunch-time. And it happened quite a lot of time that I simply forgot or could not power on due to a meeting in another building. So, one day I quickly cooked up this circuit as I was already having all the required components (including an ATmega8 development board and a relay module, to minimize the soldering job).
    Before anything further, if you try to make this circuit, WARNING!! High Voltages are involved here, extreme care is necessary while testing/operation. Ensure proper insulation for the high-voltage lines.
    This circuit can be used for powering any electrical device by setting start and stop time, which is stored in EEPROM of ATmega8, so no need to set again upon power off. RTC (based on DS1307) is used for similar reasons, no need to keep the circuit ON when not necessary, or during power off, it will maintain the date/time running (with the help of the common 3v Li button-cell). RTC setting or start/stop time setting can be changed anytime using three push-buttons provided onboard.
    Now, the main components: The microcontroller is AVR ATmega8, small enough and with sufficient flash for the code required here. Initially (before making the custom-made PCB shown in the above pics), I used a off-the-shelf available 28-pin AVR Development board from Extreme Electronics. The board is shown here:

    Using such a board avoids soldering the IC base, power supply components, ISP connector, etc. And it's having some user area for soldering, which was sufficient for this project.
    The Dual-channel Relay board used initially is from EmbeddedMarket.com:

    This module is having two independent relays with transistor circuits for activation. The VCC supply line of the coils here are connected with 9V or 12 V DC (as per the DC adapter used to power the development board) and the AVR port lines are connected to RL1 and RL2 terminals. Two devices can be independently operated with this module by connecting the AC live input to the NO (Normally Open) terminal of the Relay and taking the output from C (common) terminal to the electrical device live input. The return line of the electrical device can directly go from device to the mains, without connecting to this unit. (Note: As I was having only one device to control, I passed the Phase (Live) through one relay and Neutral through the another relay. The program operates both the relays simultaneously to power the electrical device, i.e.Tiffin-box in this case).
    Here is the Proteus simulation screen-shot (during simulation, LEDs are used in place of the relays to check the functionality):

    (The Proteus simulation files are included in the source code download at the end of the post).

    As shown, upon powering on, after displaying a welcome message, the LCD displays current date and time, and the output status (via two relays). The output ON is also indicated using a Red LED on the circuit. The terminal (UART) in the circuit is kept extra, in case someone wants to use terminal instead of LCD and push-buttons to display/set timings (This further reduces the hardware onboard, it will add only a UART-USB converter module for PC/laptop connection, which are quite commonly available).
    The program reads the set-time in EEPROM by checking for a valid EEPROM signature. If time is not set, it sets default time of 1225 HRS for start time and 1305 HRS for stop time. Whenever a new time is set, it's stored in the EEPROM and used during operation thereafter.
    The quickly made proto of the circuit with whatever came handy is shown here (underneath the LCD are the AVR and relay boards with the rest of the circuitry):

       Even the holes for accessing the three push-buttons are made up with hot soldering iron 😊, and I use a toothpick (with the blunt end) to operate the buttons inside!! Anyway, the main thing is, the 230V lines are properly screwed and totally insulated using glue-gun, including the relay terminals, so that not even a single strand of the wire comes out of the insulation.
     Of course, the circuit can be totally tested (or time can be set/ changed) without connecting the 230V lines, as we can confirm the continuity of the relay line by checking with multimeter. The high voltage line is necessary only during the actual operation.
    Later on, the schematic and layout of the PCB were designed using KiCad (latest version 5.0), as KiCad has recently become a really great tool (and free, too!), as compared to my quite earlier experience with it. I instantly liked it even better then the EAGLE lite, which I had been using so far.
The schematic is given here:

       The PDF schematic can be downloaded from here.

The operation of the circuit is described here:

Circuit Operation:
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 O/P: ON/OFF status in the second row.
 Normal Operation:
  1.  When the circuit is powered NO without pressing the 'SET' button, it displays "Welcome.." message for two seconds and then directly enters into the normal mode
  2. During the normal operation, the LCD display will be as per the above step 9. The Date and time are continuously updated on the display every second
  3. In the normal operation, whenever the RTC time matches with the Start Time, the Relays are energized, connecting the output lines with the respective input lines. 
  4. When the output is ON, as soon as the RTC time matches with the Stop time, the relays are turned OFF, cutting off the output
  5. The output ON and OFF are displayed on the LCD as well as indicated by Red LED ON and OFF, respectively
Setting Start/ Stop time:
  1.  Start and Stop time can be changed anytime  during the normal operation
  2.  Pressing the 'SET' button during normal operation displays currently set values of Start and Stop (End) times in "S:HH:MM E:HH:MM" format in the second row, where 'S' indicates Start time and 'E' indicates End (Stop) time. 'HH' and 'MM' are hours and minutes, respectively. The first row continues to display current date and time.
  3. During step 2, if 'SET' button is pressed again, display goes back to normal operation. But if 'UP' or 'DOWN' button is pressed instead, the program enters into the Start/Stop time setting mode, where "Start Hour: XX" is displayed in the second row.
  4. Use the 'UP'/'DOWN' and 'SET' keys to adjust Start Hour, followed by Start Min (Minutes), then Stop Hour and Stop Min. Each value is stored by pressing the 'SET' button.
  5. After the Step 4, the new values are stored in EEPROM and normal operation resumes.
       Here are two more views of the operational unit with custom PCB:

  • After RTC and Start/stop times are set, no intervention is required for circuit operation
  • Whenever necessary, the circuit can be switched off, the date/time settings will be maintained
  • If the circuit power is OFF and the start time is missed before the power is ON, the circuit will not set the o/p even if the Stop time is still quite away. It will set the o/p only when the next start time match with RTC. (This can be changed by minor modification in the code, if necessary).
  • Warning again, proper insulation and extreme care from high voltage line is must!! Never keep you high voltage outlet pins 'Male' type, always use socket type. Use 'male' types only for the high voltage 'inlet' pins.
    So, for last couple of months, I connect the Tiffin with the circuit (first thing after reaching office), using standard 230V AC plug, and power ON the circuit, check the display for normal operation and then continue with my work. The Tiffin gets ON and OFF as per the set time before lunch. At lunch time, I turn off the power (coz it's not necessary till next morning) and enjoy the hot meal!! The power can be kept ON also, if desired. For example, in case if you want to water your plants periodically by turning on the electrical motor, whether you are available nearby or not.

Here is the complete source code in AtmelStudio7 project files along with the Proteus simulation files:


Source Code and Simulation Download

KiCad Project Schematic, PCB and Gerber files

Datasheets:   ATmega8,   DS1307


Thanks & Regards,
CC Dharmani 

Tuesday, May 10, 2011

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.

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

Download project files
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)

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