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
    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.

  2. grahamit

    New Member

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

    AAC Fanatic!

    Jan 18, 2008
    We have just had a very long thread in which the OP used that circuit:

    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.

  4. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    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

    Distinguished Member

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