help in heat sensing and light sensing

Discussion in 'The Projects Forum' started by toto_na16, Jun 30, 2009.

  1. toto_na16

    Thread Starter Member

    Jun 30, 2009
    11
    0
    i have a project that activate an ac fan when the temperature is 25 c or above and there is a light in the room


    i tried to design a circuit which consist of heat sensor and light sensor and AND gate and Relay

    when i drew heat sensor circuit and simulate it in multisim and used an oscilloscope it give 4.950 v when on and 36.508 mv when it is supposed to be off

    and the same in light sensor


    when i added them to an AND gate and the two sensors is on it gives exactly 5v


    when one is off and one is on it gives also 5v


    i attached the three circuits via multisim


    http://rapidshare.com/files/250333500/circuit.rar


    thank u in advance
     
  2. toto_na16

    Thread Starter Member

    Jun 30, 2009
    11
    0
    no one have any ideas
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You should have posted screen prints (.PNG format preferred) instead of putting Multisim format files compressed together in .rar format on a strange server.

    Not everyone has Multisim installed.
    Not everyone has a .RAR decompression utility installed.
    Many aren't willing to download files from another server.

    Try using the "Go Advanced" feature and "Attach Files" that are in .png format.
     
  4. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    yeah, stay away from downloading stuff you dont trust. RAR files from a site named "rapidshare" sounds scary. although i know both well i suggest the avg joe not to open or download anything you dont trust.

    sorry, i am just a security (CISSP) guy.....

    I've used multisim before, found some odd results with some basic circuits. perhaps try LTspice from LT.
     
  5. toto_na16

    Thread Starter Member

    Jun 30, 2009
    11
    0
    sorry for late but i was in vacation

    here is


    heat sensor

    [​IMG]




    light sensor


    [​IMG]



    final


    [​IMG]
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    1) You do not have a ground symbol on either of your comparator circuits. Place one on each negative rail.

    2) Double the values of R4 and R8.

    3) R5 and R6 are much too large. 1.5k Ohms is a typical value for a single comparator output pull-up resistor.

    4) You could dispense with the AND gate entirely. Connect the outputs of the two comparators together, and use a single 1.5k pull-up resistor. This will result in a wired AND configuration.
     
  7. toto_na16

    Thread Starter Member

    Jun 30, 2009
    11
    0
    i don't understand the note no.1

    and the note number 4

    i can't remove AND gate because it is a project required component
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    1) You do not have a ground symbol on either of your comparator circuits. Place one on each negative rail.

    This means to connect a ground symbol to the negative (-) side of each of the batteries, V1 and V2.

    OK, so instead use a CMOS 4081 AND gate.

    However, your 7408 AND gate may work if you reduce R5 and R6 to 1.5k Ohms.
     
  9. mr boss

    Member

    Jun 3, 2009
    11
    0
    I don't know which version of multisim you use, but either way you do need a ground symbol. When I draw a circuit in my multisim, and I simulate it without a ground it gives me a error and stops the simulation immediately
     
  10. toto_na16

    Thread Starter Member

    Jun 30, 2009
    11
    0
    note : i replaced LDR and thermistor with R7 and R1 respectively

    i made these changes u said

    [​IMG]


    but thr circuit doesn't do the function

    when thermistor become above 10 k the output goes 5V
    and when LDR become less than 10 k it goes 5V

    that doesn't do the wanted function


    note : this an NTC thermistor
     
  11. toto_na16

    Thread Starter Member

    Jun 30, 2009
    11
    0
    i am using multisim 10.1
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    No, you did not. Did you even read what I said to do?

    You need to have the static resistors be significantly larger than the variable resistors, otherwise the comparators will never have a trigger point.

    R5 and R6 need to be reduced to 1.5k.
     
  13. toto_na16

    Thread Starter Member

    Jun 30, 2009
    11
    0
    ok i am sorry


    [​IMG]


    i doubled R4 and R8 in this circuit as you said

    but when the variable resistor R1 become under 100% it is supposed to give an output of 5V but it doesn't do

    why ?
     
  14. toto_na16

    Thread Starter Member

    Jun 30, 2009
    11
    0
    hiiiiii everyone anybody has any idea ?
     
  15. kammenos

    Active Member

    Aug 3, 2008
    127
    0
    Check the third circuit in row. I have test it and it works.

    Light_Dark_Activated_Relay
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    My mistake; sorry. R4 and R8 should be 5k, not 20k.
    Reduce R5 and R6 to 1.5k.
     
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    Don't worry guys, I have pretty powerful security and the RS he hosted is legitimate.
    I can correct the circuit if all fails cause I have multisim. Just let me know

    Rifaa
     
  18. millwood

    Guest

    the circuit you designed will work this way:

    1) U1A: if R1 > R4, it outputs 0v; otherwise, it outputs 5v;
    2) U2A: if R7 > R8, it will output 5v; otherwise, it outputs 0v;
    3) U3A: it outputs 5v if both U1A and U2A output 5v; otherwise, it output 0v.

    so in your current design, and with the current resistor values, U1A will always output 5v and U2A will always output 0v; thus U3A will always output 0v.

    whether that's what you wanted, I have no idea.
     
  19. toto_na16

    Thread Starter Member

    Jun 30, 2009
    11
    0
    when i made it 5k in all cases it gives 0v i think that multisim is poor i cant find any mistakes this time
     
  20. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Post an image of what your circuit looks like now.
     
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