Gating 555

Discussion in 'The Projects Forum' started by peterb33, Apr 21, 2010.

  1. peterb33

    Thread Starter Member

    Jun 10, 2009
    10
    0
    I want to apply 20,000 ttl pulses at 2.4khz to a stepper motor driver to make the motor turn for a specific number of revolutions and then stop, press a reset and repeat.

    I am using a 555 as the oscillator and 4017's as the divider (because I have them in stock), the specific o/p from a 4017 drives a transistor when it reaches the number pulls pin 4 of the 555 down to stop it. As the 4017 stops on a high I reset the counters and it repeats.

    It works but of course as I am resetting the counters they are not counting, the 555 is sending a stream of pulses out and the count ends up being wrong.

    It looks like I need to gate the pulses somehow, anyone have any advice to offer on this?

    Sorry not have a circuit, it is just a few scribbles on a pad at present!

    Peter
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Stepper motors don't start and stop instantly. You need to slowly ramp them up towards their maximum step rate, and then slow them down before you stop them.

    Either that, or step them at a slow rate.

    With no data for the stepper motor, no schematic, and very little to go on, I'm afraid you're not going to get much help.

    If you need a better way to create a schematic, download the shareware Cadsoft Eagle. Google is your friend.
    Sparkfun.com has a decent tutorial on Eagle here:
    http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=108

    If your project is not well-documented in the form of a schematic, it does not exist!
     
  3. kingdano

    Member

    Apr 14, 2010
    377
    19

    good advice.

    documentation is huge.

    i like to even document my own thought process and calculations - it helps to find flaws in component selection, or topology if you review your own notes.

    i tend to document meticulously, because in a corporate environment projects are dropped and restarted all the time - if in 2 years i need to pick up an old design and remember why i did things i know i will have a fairly detailed record.

    for the home hobbyist maybe not so critical to be as detailed, but keeping records of calculations and schematics, and even testing and documenting circuit behavior can help you really understand what is happening.

    none of this can happen without an accurate schematic to refer to and annotate.


    edit: plus when you come on message boards asking for help, we will all have stuff to refer to :)
     
  4. peterb33

    Thread Starter Member

    Jun 10, 2009
    10
    0
    Thanks for the reply, fully appreciate what you say. I have never really got to grips with being able to put a schematic together on screen as I am not CAD literate but take your point and will do some downloading.
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    It doesn't have to be fancy, just hand draw it as legiably as you can, scan it, and upload it. PNG format is prefered, but .gif works too.
     
  6. peterb33

    Thread Starter Member

    Jun 10, 2009
    10
    0
    I want to apply 20,000 ttl pulses at 2.4khz to a stepper motor driver to make the motor turn for a specific number of revolutions and then stop, press a reset and repeat.

    I am using a 555 as the oscillator and 4017's as the divider (because I have them in stock), the specific o/p (p4) from the final 4017 drives tr1 on when it goes high pulling pin 4 of the 555 down stopping the pulses. As the 4017 stops on a high pressing the reset sw resets the counters and also charges the 1uf capacitor. This capacitor keeps tr1 on for a short time, when it is discharged tr1 is off starting the pulses from the 555 and repeating the cycle.

    Amazingly it works but the number of pulses I am recording varies from 18905 to around 18914 which is a bit short of the 20,000 I need
    I would be grateful for any advice, sorry about the quality of the schematic
    Thanks Peter
     
  7. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Which POT are you using on the 555, and what resistance to you read at the point it is set at?
     
  8. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,159
    I'm assuming your 555 is set for 20kHz and your divider is suppose to divide that down to 1 Hz. The way it's wired your dividing down to 0.2 Hz.

    What I don't see is an output meeting your description, 20000 TTL pulses at a 2.4 kHz rate.
     
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