Sunday, February 14, 2016

Pellet burner contoller

Pellet burner controller is the most challenging project that I have worked on. This is the detail describe of it.

Some explanations before I start: 

  • Pellet fuels are heating fuels made from compressed biomass.
  • Pellet burner is burner which use pellet for fuel.
  • Pellet burner controller is an electronic used for manipulating pellet burners.

Pellet burner controller hardware description

On the next two pictures, picture 1 and 2 are represented the front and back of a pellet burner controller.

Picture 1. Front of pellet burner controller

Picture 2. Back of pellet burner controller

Parts of pellet burner controller from pictures 1 and 2:

  1. Easy TFT Board is 262K RGB colors display with touch panel, ideal for human-to-burner interface.
  2. Ethernet MCU card with LM3S9B95 microcontroller, which has a relatively important rolein the whole system.
  3. Digital input for photocell and thermostat, and analog input for NTC resistor. NTC resistor is reserved for measuring temperature.
  4. 230V AC input and AC output for burner’s fan, igniter and cleaner. The burner’s fan’s use is to insert air into the burner. The power of insertion must be precisely controlled and this is a serious real time purpose for the microcontroller. The burner’s fan is an AC one phase electromotor and it’s work is controlled by a triac. The microcontroller detects every time when a power sine wave goes through zero. When it comes through zero, the microcontroller starts the timer. When the timer stops counting down, the microcontroller sends an impulse to triac. The triac will give at that point a sufficient voltage to the burner’s fan. This is the way how the microcontroller hashes power sine wave, and controls the burner’s fan power. The zero cross interface circuit is my design. Every example of the circuit that I’ve found on the internet, at some point and some way didn’t worked properly. Between the microcontroller and triac is the optotriac. The igniter and cleaner also uses a triac. In those cases, there is used an optotriac with zero cross. The interface between the microcontroller, igniter and cleaner acts like a solid state relay. 
  5. 12V or 24V DC input and output for two feeders. Two feeders are a DC electromotor. The interface between the microcontroller and feeders are mosfet transistors and optocouplers. In that PCB region are place for solder interface for DC cleaner. This is a full bridge interface for the DC electromotor which can go forward and backward.
  6. 3.3V voltage regulator.
  7. The Ethernet Connector Board’s use is to connect the pellet burner controller and the PC. The pellet burner controller is working like a small web server. This is the most practical and effective way to connect the controller and the PC, no matter which operating system does the PC possess. Why should the user always have to go down to the basement for turning the pellet burner on and off? Now the user can control the burner directly from his PC, which eliminates the need for a person to actually be physically present by the burner, and excludes the act of directly interfering with the device. This function is now still under development. 
  8. USB connector for 5V power and update microcontroller software with help of USB bootloader.
  9. MikroBUS socket for GSM click. The user have an option to control the pellet burner with a simple SMS messages. This function is also still under development.
  10. Real time clock with battery.
  11. Connector for mikroProg for ARM.
  12. Input for temperature sensor DS18S20 and thermocouple. The DS18S20 can be used for measuring water temperature in the system or to measure the room temperature. The thermocouple’s use is to measure smoke temperature. The thermocouple interface is MAX31855K.

Pellet burner controller interface description

On the picture 3 are two options of the main display. The bought options have MENI button in upper left corner. The ‘Time and Date’ info is in the upper right corner. In the green area of the display is shown the burner’s work phase.The ‘T DIMA’ shows temperature of the output smoke. The ‘T AMBIJENTA’ info shows the system water temperature. The red button in the lower right corner is for turning the device on and off. On the left side of picture 3 is a display for an automatic workfucntion. There are two buttons for setting the goal system water temperature. On the right side of picture 3, the display for manual work is visible. There are five buttons available from P1 to P5 for adjusting the burner power. In this case P1 is the lowest power and P5 is the highest power. One note: interface is on Serbian.

Picture 3. Main display, left is automatic work, right manual work

Overall, the pellet burner controller has many functions. Since this document is a short and dense version of the whole concept and idea, additional details, finesses and further elaborations will not be shared on this occasion. Generally all the functions, modes and options will be described in the full version of the included user’s manual. For an additional info, there is something interesting that I would like to mention also; 

  • The Chrono-thermostat’s use is for programming the device when it’s automatic mode turns on/off or set to some certain power level. The Chrono-thermostat display is shown on the picture 4. An example from picture 4: the pellet burner will turn on every Monday at 1:30 AM manual work P1.
Picture 4. Chrono-thermostat display

  • The pellet burner controller has 42 parameters for adjusting operation. The parameters must be adjusted by a servicer, and regular user interference should be totally avoided and excluded in this scenario. For this reason, there is a password protection implemented. After a successfully and correct password entry, the servicer can adjust parameters as needed. Some of the parameter has a test function. The display for password and parameter adjustments is shown on picture 5.
Picture 5. Left is display for password, right is display for adjust parameters.

  • There are basic functions like adjust time/date and display calibration. The functions for language, adjust GSM and IP address are still under development. On picture 6 
  • are shown the ‘main menu’ and the ‘settings menu’.
Picture 6. On left side is main menu, on right side is settings menu.

Pellet burner controller first version

The first version of the pellet burner controller is working in a pellet factory for more than two years now. It’s embedded in a steel box case. The first version is much more simpler than the latest version. It has PIC microcontroller and 16x2 LCD display. On picture 7 and 8 is the first version of the pellet burner controller.
Picture 7. Front side of first version of pellet burner controller

Picture 8. Back side of first version of pellet burner controller

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