Temperature Controller using PIC16F628A

Discussion in 'Embedded Systems and Microcontrollers' started by bentech4u, Oct 27, 2008.

  1. bentech4u

    Thread Starter New Member

    Oct 27, 2008
    8
    0
    hello friends

    i want Temperature Controller using PIC16F628A

    the sensor of the temperature controller is thermocouple

    i am a newer in PIC section

    my concept is that the output of the thermocouple is given to a amplifier

    the display might me 7-segment display

    please help me friends

    give me the circuit & code

    thanks in advance
     
  2. bentech4u

    Thread Starter New Member

    Oct 27, 2008
    8
    0
    http://www.machinegrid.com/content/view/51/1/

    please see this circuit

    i want such type of circuit

    but in this circuit,there is no amplifier placed on it

    which amplifier is suitable for that..?

    and the display unit of this project is LCD..I want only 7-segment display

    so please guide me friends to make a suitable circuit & code

    thanks
     
  3. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    First up we can provide help and advice with your project but we are not in the business of supplying circuits or software on demand.

    Before we can provide any meaningful advice we need to know exactly what you are trying to do.

    1. What temperature range and accuracy do you need to measure.

    2. Is there reason for your choice of PIC16F628? Unless you are going to use a separate A/D converter the 628 is a bad choice.

    3. Do you have to use a thermocouple or can you get away with using a solid state temp sensor? Thermocouples have a greater temperature range but are a lot harder to use so this relates back to question 1

    4. Do you have to use a separate amplifier or can you use an interface chip that does the amplification and A/D conversion for you. Stand alone thermocouple amplifiers can get very messy.

    5. Why does the display have to be LED? An LCD display is easier to use but there might be valid reasons for using a LED display.
     
    Last edited: Oct 28, 2008
  4. bentech4u

    Thread Starter New Member

    Oct 27, 2008
    8
    0
    1. the temperature range must be 0 to 1000

    2. Is there reason for your choice of PIC16F628? Unless you are going to use a separate A/D converter the 628 is a bad choice.

    2. Boz me just buy 2 PIC16F628A:confused:..that's why..which is the suitable IC for that..?

    3. yes , I hav a thermocouple (Chromel - Alumel)

    4. No i don't hav an amplifier..i talk about the amplifier boz the output of the thermocouple is very low voltage na....that's why


    5. Because 7-Segmet displat reduces the production cost..also i have a cover for a temperature controller
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    For the amplifier i suggest you to use a FET input op-amp which needs a tiny bias current connected as voltage follower (which has a very high input impedance as not to load your thermocouple) and then use a non-inverting amplifier to amplify the voltage to a reasonable level. Note that the greater the gain the more amplified the noise will be along with the signal. Also, its better to use a precision amplifier as to reduce the offset bias current and offset voltage and have a more accurate reading. About the PIC is better to choose one with a build-in ADC, it will reduce your circuit complexity and cost.
     
  6. bentech4u

    Thread Starter New Member

    Oct 27, 2008
    8
    0

    please suggest a suitable PIC
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    One that came in my mind now is the 16F819. It is a 18 pin device but it is enough to drive four seven segment displays (to show values up to 1000) and it has build-in ADC. Note that to drive these four displays you will need to use 11 I/O pins (if you are going to use the dot sign on the displays you will need 12 pins), you will use 4 of the 11 pins to switch the displays in sequence at a fast rate as your eyes to see all the displays on at the same time because of the phenomenon of the persistence of vision and the other 7 pins of the 11 to put the right number on each display at the time it will be switched on.
    If you want visit www.microchip.com to see more PICs and choose one.
     
  8. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    Rather than mess about making your own amplifier I would use a thermocouple interface chip. The MAX6675 springs to mind http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3149 but there are others chips from other manufacturers that do the same job. A google on "thermocouple interface" will bring up plenty of hits. The chip has an amplifier with cold-junction compensation and its own A/D converter so you can use your pic16f628.

    For the LED display you can either do it all in software in the PIC or use a 7 segment LED driver/decoder chip and just feed it the BCD code for each digit, once again there are plenty of chips around, do a google. Which way you go depends on your priorities of development time vs production cost.
     
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