Design help, 555 monostable

Discussion in 'General Electronics Chat' started by hspalm, Jan 31, 2011.

  1. hspalm

    Thread Starter Senior Member

    Feb 17, 2010
    I am preparing for the 555 contest and was hoping I could get some advice before I start hooking up.

    It's not the 555 circuit that needs help (I think), but rather the part of making a motor spin.

    The idea is to use a potmeter mounted on a big joystick to adjust RC time constant. The further back the joystick is pulled, the longer the out pulse time on the 555 when triggered, and the more charge the big capacitor gets. I want to push the SPDT switch to release energy to dc motor wich will spin more powerfull the further back the joystick was on trigger (555 trigger). Motor will be connected to mechanism to send some particle flying to a basketball hoop or similar (really small scale). Am I getting things right here?

    I want to handle the timing part of the circuit, it's the motor/capacitor part I could use some advise on!

    Thank you :)

  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Might want to take the contest part out, so competitors don't get more ideas. ;)

    Take the 555 completely out of the picture, that will help you picture it.

    You are trying to have the motor turn on with varying toque depending on the value of potentiometer. This would mean either a stepper motor, changing the step speed rapidly, or varying PWM control of the motor. Both of which would need extra circuitry, preferably 555 based.

    Hopefully that gives you a starting point, and good luck, I'll help more if I come up with more ideas, not in the contest here.
  3. magnet18

    Senior Member

    Dec 22, 2010
    EDIT, just caught this part of your question, i apologize if my post is unwanted info, you may not want to read it...
    is there spoiler code tags?

    Hmmm, I'm sure bill or someone will correct me if Im wrong here, but i think it might work well to make the 555 astable, with the pot on pins 6, 7, and 8, this adjusts the time constant nicely

    Usual disclaimer, i don't have much experience, so don't take anything i say for granted
    Last edited: Feb 1, 2011
  4. Wendy


    Mar 24, 2008
    AAC has local hosting for pictures. I translated yours to use as an attachment. I agree with TOG, don't advertise you are entering a contest. I may be entering the same contest, for example, but I always encourage new ideas.


    You have a problem with your schematic. Right now your motor is switching between ground and open, nothing happening. You may want to connect your motor on the common lead. I don't see the advantage of what you're trying to do, but it is always fun to experiment.
  5. hspalm

    Thread Starter Senior Member

    Feb 17, 2010
    I clearly see what mistake I have made. My idea was to charge the capacitor with energy dependant on the output pulse width of the 555. I see now I should have connected motor to both ends of the capicator, and isolate the cap and motor when I press the button. I will post a new picture very soon! I also like the idea of using it in astable mode, so the motor starts spinning with more torque dependant on the duty cycle. I have actually considered a very similar solution, the only thing is that it does not actually allow me to design anthing, as its only a standard astable circuit with a transistor on the output...

    Magnet18; all feedback is appreciated, keep it coming and thank you.
    To all others, thank you, this far!