another ne555 \ lm393 Signal Generator - help pls

Discussion in 'The Projects Forum' started by signupsr, Mar 16, 2012.

  1. signupsr

    Thread Starter New Member

    Jan 21, 2011
    13
    0
    Hello,

    i love these 555's been using them for 15 years, and your resident expert bill does some nice work - his circuits displayed throughout the website all run cool and clean - elegant and thorough work. thankyou kindly.

    im not familiar with comparators though, - not that you need too be, - or so i thought.

    http://forum.allaboutcircuits.com/c...uits.com/picture.php?albumid=45&pictureid=665

    im getting a lovely identical triangle wave from pins 2 and 6 - and a 50\50 square wave from pin3

    but connecting it too pin 2 of the comparator with all the designated components - except a resistor and led as a load.

    no matter how i twiddle the pot on the 393 i cant get the signal on the output - measuring it on a cro - been playing for 2 hours tried these comparators seperatley too make sure operational - ebay cheepies- but that seem too work fine otherwise -

    not getting any love from the 393 despite bills clean inputs

    cheers AAC's
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,658
    632
    That sure is a simple circuit, but simple circuits are often the easiest to connect incorrectly.

    But first, just to make sure: It is the case that when the comparator is connected, you get a sawtooth waveform from 1/3 Vcc to 2/3 Vcc on the comparator input?

    I suggest that you remove the transistor since you aren't using it because you might have it connect incorrectly, causing the problem.

    Double check your other connections.

    Do you have a power supply connected to the LM339? (Pin 3 to + and pin 12 to ground for the 14 pin DIP.

    What are you using for Vcc ?This circuit should work with a Vcc of 4.5 volts or higher when using the LM555, and 2V or higher with the LMC555.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    We often recommend pictures here. This site is about the friendliest I've ever seen on that front, you can download pictures to both albums and attachments. If you need help just ask.

    Everyone one makes wiring errors, if you're lucky the part survives. If your not, you wind up with reversed brands of part numbers on your fingertips, voice of experience speaking.

    One more post on your count and you get the full benefits of being a member here. Hit and run Homework types ruined it for everybody, you need 10 for all the features to work on this site.

    Thank you kindly for the nice words. I'm blushing. Really!
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    Are you using the 'pull-up' resistor? The LM339 can only sink current not source it. So it needs a pull-up resistor (R8 in your link) to work.
     
  5. signupsr

    Thread Starter New Member

    Jan 21, 2011
    13
    0
    oh my goodness , a pullup resistor,

    that i didnt have,

    - but all the connections have been checked fastidiously

    ive still got the circuit pushed over too 1 side of my breadboard so i will try the pullup resistor shortly and upload a picture thisafternoon - however the circuit is driving a flyback in resonance really nicley through a irf 640 and pulling 1.5" inches... dispite the 75% ish duty cycle, quite surprising i think

    pullup resistor... never been so happy too kick myself,

    thankyou guys.
     
  6. signupsr

    Thread Starter New Member

    Jan 21, 2011
    13
    0
    hmm my snubbers definitely needs work aswell,

    when i was testing the flyback circuit last night i got a momentary flicker from my lcd screen, but now, the background light is flickering from white too blue constantly, and getting worse... as i type, hmm ghosting on an lcd ?... thats a new one...

    also has anyone come across anywere a inductance \ capacitance circuit etc that they suspect will be effective for electrolysis, we only used straight DC and AC in highschool science, or other circuit that may be better than pulsed dc

    cheers,
     
  7. signupsr

    Thread Starter New Member

    Jan 21, 2011
    13
    0
    oh actually the subwoofer was the cause of the screen flicker

    "pushes cable back on"

    but co-incidentally the bench top psu is playing up... intermittently... one thing at a time as always........
     
  8. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    That is how it is done. You eat an elephant one bit at a time.

    BTW, it is about time for my upgrades to the article. Since you have fresh eyes on it, please feel free to make suggestions. It originally started as a tutorial to help people new to LEDs, and bloomed from there.
     
  9. signupsr

    Thread Starter New Member

    Jan 21, 2011
    13
    0
    haha flattered for sure, but despite starting young (turned 28 yesterday) electronics is never something ive been a natural at, despite dropping out of year 11 highschool too study full time electronics -... Australian public school teachers are not all inspirational

    i find its all about a delicate balance of deductive reasoning and patients,
    and racing cars is the pace i prefer too operate at...

    however i would be honored too help with some simple revisions were i see fit,

    namely the 2 minor issues i was stumped on yesterday, and il get my notebook out for the future confusion,

    Bill, who should email the ideas and modified image (s) too ?
     
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