Relay-Timer Circuit with RTC (for auto-operating appliances) using AtmelStudio or Arduino

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 and the serial terminal is unused):

 
  Following is the simulation using ATmega328 (Arduino):

 (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 1230 HRS for start time and 1300 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):

       The 230V lines are properly screwed and totally insulated using glue-gun inside the box, 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 (when using Arduino, replace ATmega8 with ATmega328 in the circuit, in the same PCB):

       The PDF schematic can be downloaded from here.

The operation of the circuit is described here:

Circuit Operation:
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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 ON without pressing the 'SET' button, it displays "Welcome, -Relay timer-" 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:
     

 Notes:

• 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 and Arduino project files along with the Proteus simulation files (please ensure programming the fuse bites for proper clock frequency values). When using Arduino, ATmega8 needs to be replaced with ATmega328:

Downloads: 

Source Code (AtmelStudio) and Simulation Download (ATmega8, @8 MHz internal clock)

Source Code (Arduino) and Simulation Download (ATmega328, @16 MHz External clock)

KiCad Project Schematic, PCB and Gerber files

Datasheets/ Links:   ATmega8,   ATmega328,   DS1307,   Arduino Website


Enjoy!!

Thanks & Regards,
CC Dharmani 
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Make-Yourself ATmega32 Starter's Kit with LCD, I2C, SPI, RTC, ADC interfaces

Hi friends,
here is my home-made kit of ATmega32 microcontroller interfacing. The ATmega32 controller is rich with features like onboard 32kB in-System programmable flash, 1 KB EEPROM, 2KB SRAM, 10bit ADC (8 channel), SPI bus inteface, TWI (compatible with I2C bus) interface, an USART, analog comparator, etc. That's why I've selected it to load my kit with all those features.

This M32 card is having an LCD inteface with contrast adjustment, an RS232 port for connecting with PC, a connector for 8 analog voltage inputs to measure by ADC, a Real Time Clock IC DS1307 from maxim with battery back-up, four general purpose keys, two keys for generating interrupts and an LED.
The circuit can be powered by an easily available 12v DC adapter. The voltage regulator IC 7805 used to convert the input into regulated 5v supply.

See below the kit in powered on condition and the schematic (click to enlarge the images)













The PCB is completely home-made, using the etching technique with the Ferric Chloride chemical. If you want to know how to make a PCB yourself from your layout, visit following webpage, it's really helpful:

http://electrons.psychogenic.com/modules/arms/art/10/pcb_howto.php

The schematic and layout of the M32_card shown here are prepared using EAGLE. It's a single layer board for making the home-preparation easy. Check out the bottom layer and the layouts in the pics below:












The software for the ATmega32 controller is written using imageCraft AVR compiler. The software contains code for LCD interface, use of RTC and communication with PC with RS232 port. Using the Hyper terminal in windows, the functionality of the kit can be checked, as I've mentioned in my previous post of RTC_EEPROM interface with ATmega128.
Sown below are the pics of RTC circuit in test and related screen shot of the hyper terminal while interacting with the M32_Card

















Here is Proteus ISIS Simulation:



The complete source code files including new addition of ADC (check out Here) can be downloaded below.


Download
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Source code
PCB files (in PDF & EAGLE formats)Proteus Simulation Model

Datasheets:

ATmega32 DS1307 MAX232

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ccd@dharmanitech.com

Interfacing RTC & serial EEPROM using i2c bus, with ATmega128 uC

Hi friends,
here is my experiment with i2c bus for interfacing serial EEPROM (24C256) and RTC (DS1307) using AVR microcontroller ATmega128. The circuit is also provided with an RS232 port for connecting with PC to send commands for reading/writing EEPROM or setting date/time in RTC (Click on images to enlarge them).

Communication with PC is done through Hyper Terminal. A screen shot of the message sent to PC by microcontroller immediately after power ON is shown in the figure at the left, where the user is asked to enter choice from the menu options related to EEPROM and RTC. User can store data in EEPROM, or set RTC date and time by entering them using PC keyboard.
Hyper Terminal is used with 19200 Baud, No parity, No hardware flow control settings.

When the circuit is powered on, a welcome message is displayed on the Hyper Terminal window and a menu with 9 options (0-8) is displayed (refer to the figure). The options are explained here:

0: Erase EEPROM (fills eeprom with 0xff bytes)
1: Write EEPROM (starts writing eeprom starting with 0x0000 address)
2: Read EEPROM (reads eeprom starting with 0x0000 address)
3: Write eeprom page (writes one page of eeprom at specified page number)
4: Read eeprom page (Reads one page of eeprom at specified page number)
5: Display RTC Date (Displays current date from RTC)
6: Display RTC time (Displays current time from RTC)
7: Update RTC Date (Setting new date in RTC)
8: Update RTC time (Setting new time in RTC)

The option is selected from PC keyboard. While writing to eeprom or RTC the data is entered using PC keyboard as specified by the program.

The software routines include DS1307 library, 24C256 library & I2C library along with the main function.

The code is written in C using winAVR (inside AVRStudio). The complete project folder can be downloaded here in zip format (updated on 25-April-2009, earlier it was in ICCAVR format):

Here is running simulation on Proteus ISIS (click on image to enlarge it):


Downloads
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Complete Source code (winAVR, AVRStudio-4 format)
Proteus Simulation Model

Datasheets:
ATmega128,  DS1307,  FM24C256,  MAX232

Thanks!

(last updated on 25-April-2009)
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ccd@dharmanitech.com