Idea's On Basic Duty Cycle Generator?

Discussion in 'The Projects Forum' started by NFA Fabrication, Jan 4, 2014.

  1. NFA Fabrication

    Thread Starter Active Member

    Aug 12, 2012
    I want to build a basic duty cycle generator. I assume a 555 timer will be used. It will be used for general projects, and a fixed frequency would most likely work just fine. I would like to be able to use it for motor speed control, "Dimming" LED's, and various other things. I found this diagram at listed as an "LED Dimmer":


    I would guess that the "LED Dimmer" is basically a duty cycle generator (Says 5%-95% adjustability), but I can't even get their diagram to work for it's intended purpose anyway. I don't quite understand how that potentiometer with those 2 diodes facing the same way connected to it would do anything either. Thoughts? Better idea's for my project?
  2. #12


    Nov 30, 2010
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    One of those 1N4148 diodes on the left should be reversed.

    And there should be a 470 ohm resistor in series with the pot wiper to prevent overcurrent into the discharge pin (pin 7).
  4. NFA Fabrication

    Thread Starter Active Member

    Aug 12, 2012
    I was pretty sure on the diode thing, as it looked odd, but I am kind of a newb, and didn't want to look like I was jumping to random conclusions. I will work on this tomorrow and see if this works out. The previous poster had some links that were promising, (I was already reading through one of them before he had posted it), but it dealt with components I do not have, or was out of my current knowledge range on the topic. hanks! I hope I can make something work with the components I have. I do have quite the stock pile of stuff, so with any luck...
  5. Little Ghostman


    Jan 1, 2014
    If your wanting to drive motors it might be an idea to put some kind of transistor or MOSFET pass circuit on the output of pin 3, that way you can drive higher currents, but obviously depends how much current your going to need.
    I normally put a mosfet on with a flyback diode anyway, then i can use it as a quick tester for motors.
    I just finished a project on another forum for making sounds for a toy gun, i used 2 555 timers (actually I used 1 556 which is a dual timer), I will dig out my notes later and post the schematic, that way you can also vary the frequency if you want. You dont have to use 2 by the way, but it gave me more options
  6. NFA Fabrication

    Thread Starter Active Member

    Aug 12, 2012
    Yeah, I know the limitations of the output, I just need a reliable signal generator. Good call though, I didn't mention it.
  7. bertus


    Apr 5, 2008
    wayneh likes this.
  8. wayneh


    Sep 9, 2010
    In my opinion, the comparator approach shown in the link provided by Bertus is a better strategy than a single 555, since it gives control over the full 0-100% range while maintaining frequency.

    I agree with the suggestion by Little Ghostman to use a MOSFET switch to eliminate the 555 output properties. It may be overkill for a few LEDs but it gives you the full power supply voltage range (the 555 does not) and the load current is limited only by the MOSFET you choose. Very versatile.

    Just my 2¢