OpAmp Help

Discussion in 'The Projects Forum' started by Roiw, Dec 12, 2012.

  1. Roiw

    Thread Starter New Member

    Nov 22, 2012
    12
    0
    Hi guys!

    I have another simple project that I need help :)

    But for this one I need to make it real. ( I need to create the board and stuff)

    And I dont know which components to pick. :confused:


    I will post here the schematics of the circuit


    The Circuit

    It's a simple circuit that need to turn on a red light if the temperature of the enviroment is below 10ºC or above 30ºC and a green one if between those values.

    BUT I MUST use a Thermistor :( I'm not allowed to use a LM35 for example.

    And to make things worse the only ones I have avaliable are 20Ω ones ( But I have 10 of them, so I can at least make a 200Ω Thermistor)

    Here is a pic of the circuit I designed and it works:

    [​IMG]


    The VCC on the top OpAmp is +5 and -5

    And in the bottom one is 0 and -10v

    So, my question is:

    WHICH OPAMPS CAN I USE ?

    I need a name like LM741.

    Thanks a lot guys! :)

    EDIT: Forgot to mention! The top left resistor is in fact the Thermistor! ( The top horizontal one)
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
  3. Roiw

    Thread Starter New Member

    Nov 22, 2012
    12
    0
    Do you know if I can put (VCC+ = 0) and ( VCC- = -10) on a TL081?

    Thanks


    Edit: I mean OFFSET N1 = 0 and OFFSET N2 = -10
     
  4. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    I am not sure I understand. What is N1 and N2. They are not referenced in your schematics
     
  5. Roiw

    Thread Starter New Member

    Nov 22, 2012
    12
    0
    Sorry for that. I'm talking about the VCC+ and VCC- on the op amps.

    There is a schematic in the datasheet you gave me and they are referenced as OFFSET N1 and OFFSET N2 ( page 3 ) thats why I said that, maybe offset means something different, sorry for that I'm still learning.

    Thanks
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    Why are you using different power for each op amp?
     
  7. Roiw

    Thread Starter New Member

    Nov 22, 2012
    12
    0
    What's happening is :

    Voltage output OPAMP1 -> 5, -5

    Voltage output OPAMP2 -> 0, -10

    So when my temperature is less than 10ºC OPAMP1 saturates in 5V and OPAMP2 in 0v D1 is turned on

    When I'm between 10 and 30ºC my OPAMP1 saturates on -5 and OPAMP2 keeps on 0v
    so D1 is off and D2 is on

    When I'm above 30 OPAMP1 saturates on -5 and OPAMP2 on -10
    so D1 is on and D2 is off

    And we get the desired output :D
     
Loading...