multiple 555 servo control question

Discussion in 'General Electronics Chat' started by jtrout13, Feb 19, 2011.

  1. jtrout13

    Thread Starter New Member

    Feb 19, 2011
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    Hi, I'm new to this site.

    I am building a robotics controller for part of a junior design project at university. I am studying mechanical engineering, and would appreciate any input to this question:

    Anyway, my robot has 4 servos. I am using potentiometers from a model airplane controller to adjust pulse width for speed and direction control of modified servos. Anyway, I plan to use one 555 timer in astable mode setting a clock frequency of 50hz, triggering monostable 555's which set the pulse width. I'm sure you are familiar with this type of application. On to the question:

    Will it be okay to use a single astable 555 to trigger all 4 monostables, or do I need to set up an astable/monostable combo using a 556 chip for each servo? To reduce parts count and space in the controller, i'd like to use a single astable 555 and combine the 4 monstables on a 558 IC. opinions will be greatly valued.

    Thanks!
     
  2. grahamit

    New Member

    Dec 9, 2007
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    I found a circuit for you that should work well. It's here.
     
  3. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,685
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    We have just had a very long thread in which the OP used that circuit:
    http://forum.allaboutcircuits.com/showthread.php?t=47149

    1) The 3M3 Ω resistor is too large.
    2) The pinouts to the servo are wrong for the vast majority of modern servos -- positive and negative are swapped. The center pin on modern servos is usually positive.
    3) That circuit is for manually controlling a servo. It is a little hard to see how that would have much use in a robot.

    John
     
  4. nomurphy

    AAC Fanatic!

    Aug 8, 2005
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    It seems to me that you should be able to use a single 555 output (not all things considered), you may need to buffer the 555 output for higher drive currrent or faster edges. But, also consider that a single 555 will provide some synchronicity, whereas multiple sources will be out of sync with each other (if that's important to your design or not).
     
  5. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
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    At the point you need 4 circuits may be time to consider a microcontroller, especially at a junior level in a university.
     
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