LM324N problem!

Discussion in 'General Electronics Chat' started by kpsg25690, Mar 26, 2011.

  1. kpsg25690

    kpsg25690

    Joined:
    Mar 26, 2011
    Messages:
    4
    [SOLVED]LM324N problem!

    Hey all!
    Since this is my first post i should introduce myself..
    My name Karan and i am an engineering student.

    I have been working on a project on a project that requires a comparator.
    I am using LM324n as a comparator and the circuit is working correctly.

    I am using a +5V supply power to the ic but when the output is high i get around 2.1V on the output pin,which is enough to drive an LED but i want to give this output to a PIC18F4520 which will not identify 2.1V as high.

    What do i do?
    I have tried using a 12V supply for the IC also without any change.

    I've been at it for some time and need some help...
     
    Last edited: Mar 26, 2011
    kpsg25690, Mar 26, 2011
    #1
    1. Advertising

  2. kpsg25690

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Joined:
    Jan 21, 2010
    Messages:
    17,319
    Location:
    Mid way between Beijing and the Ronne Ice Shelf
    Show us the circuit diagram...
     
    (*steve*), Mar 26, 2011
    #2
    1. Advertising

  3. kpsg25690

    kpsg25690

    Joined:
    Mar 26, 2011
    Messages:
    4
    Here's the circuit.
    The IC gets a +5V supply.

    [​IMG]

    Thank you for the fast reply!!
     
    kpsg25690, Mar 26, 2011
    #3
  4. kpsg25690

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Joined:
    Jan 21, 2010
    Messages:
    17,319
    Location:
    Mid way between Beijing and the Ronne Ice Shelf
    OK, several things:

    1) The lm324 can't pull the output right to the supply rail when sourcing current. The specs indicate that you can expect several volts difference (you're seeing 2.9) but this will be strongly influenced by the load you're driving.

    2) You mention a LED on the output of the LM324 which is not shown on your circuit diagram. Do you only get a 2.1V swing with the LED removed? Do you have a series resistor with the LED (if not, this explains the low output voltage)
     
    (*steve*), Mar 26, 2011
    #4
  5. kpsg25690

    kpsg25690

    Joined:
    Mar 26, 2011
    Messages:
    4
    sorry i forgot the LED,my bad....
    The circuit is as follows

    [​IMG]

    i get around 2.1 V if i bypass the 2.2K resistor and use the LED directly..

    I tried it without an LED and i get 3.6 Volts and i also get the same reading if i use the 2.2K resistor as shown in the circuit

    I tried to use the o/p pin as a sink and i got 3.7V from the output pin..

    which configuration should i use?

    if i connect the output pin to the PIC18F4520 as input would the uC identify it as logic 1 (i think it should)

    and thanks for the reply..
    really helped me out man..
     
    kpsg25690, Mar 26, 2011
    #5
  6. kpsg25690

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Joined:
    Jan 21, 2010
    Messages:
    17,319
    Location:
    Mid way between Beijing and the Ronne Ice Shelf
    Yes, 3.6 is probably as high as you can expect the output to go, especially with a load.

    Remember that using a LED without a series resistor will essentially clamp the output voltage to Vf of the LED, with the current limited by the op-amp's output stage.

    That output voltage is probably good enough to be seen as high by the uC -- the specs should tell you in any case.

    If you use the output as a sink rather than a source, you may have problems getting a good low level. Test it and see.
     
    (*steve*), Mar 26, 2011
    #6
  7. kpsg25690

    kpsg25690

    Joined:
    Mar 26, 2011
    Messages:
    4
    yeah when i use the o/p pin as sink the low level is not zero but something close to 0.8V

    Thanks man! Solved my problem.
     
    kpsg25690, Mar 26, 2011
    #7
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. praveen

    DC DC converter problem (loading problem)

    praveen, Dec 10, 2004, in forum: Electronic Design
    Replies:
    4
    Views:
    1,191
    John Smith
    Dec 10, 2004
  2. praveen

    DC DC converter problem (loading problem)

    praveen, Dec 11, 2004, in forum: Electronic Design
    Replies:
    1
    Views:
    682
    Frank Bemelman
    Dec 11, 2004
  3. tasa3dit@caramail.com

    monitor problem : east west problem and pincushion effect

    tasa3dit@caramail.com, Apr 25, 2004, in forum: Electronic Repair
    Replies:
    2
    Views:
    1,266
    John Gill
    Apr 26, 2004
  4. Tim

    ST LM324N anyone have any schematics

    Tim, May 24, 2007, in forum: Electronic Design
    Replies:
    15
    Views:
    612
  5. monty1945@lycos.com

    Problem with new TV - anyone know what the problem is?

    monty1945@lycos.com, Oct 30, 2007, in forum: Electronic Repair
    Replies:
    6
    Views:
    248
    Gary Tait
    Nov 2, 2007
Loading...

Share This Page