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    555 square wave generator

    Hello, Please help me, I have designed a very basic square wave generator to run a speedometer circuit board which is providing output to control a stepper motor

    Square Wave by Jason Milich, on Flickr

    R1 and R1 are replaced with a double 100k pot, when I adjust the pot the frequency changes, my problem is, when I look at the signal on a scope it doesn't appear that the wave pulls right down to ground, I can use my soundcard and output a signal that works just fine.

    ARGHHHHH!

    alternatively, any tips on designing a cheap 4 wire stepper motor variable speed controller

    •   Alt25th May 2012, 22:04

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    Last edited by mister_rf; 25th May 2012 at 23:03.


    2 members found this post helpful.

    •   Alt25th May 2012, 22:43

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    Re: 555 square wave generator

    Quote Originally Posted by Milutiche View Post
    R1 and R1 are replaced with a double 100k pot, when I adjust the pot the frequency changes, my problem is, when I look at the signal on a scope it doesn't appear that the wave pulls right down to ground, I can use my soundcard and output a signal that works just fine.
    How low is low enough for your application? The datasheet indicates that when the output of a 555 is lightly loaded, it should swing down to 0.01V or less in the low state, and to about 0.1V at 10mA load.



    •   Alt26th May 2012, 07:19

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  4. #4
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    Re: 555 square wave generator

    Hey thanks for the help,
    pjdd, It looked to be sitting at about 0.4v on my scope, I did manage to work my way around this problem by connecting the output of my square wave generator directly to the IC driving the stepper motor. so far all is good. :)

    ---------- Post added at 20:02 ---------- Previous post was at 19:56 ----------

    Hey thanks for the help,
    pjdd, It looked to be sitting at about 0.4v on my scope, I did manage to work my way around this problem by connecting the output of my square wave generator directly to the IC driving the stepper motor. so far all is good. :)



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    Re: 555 square wave generator

    would it be easy to reverse the stepper motor using this circuit? I've come across a bunch of 6 wire steppers that might be more suitable for my application

    http://www.eleccircuit.com/4013-and-...stepper-motor/

    Cheers

    EDIT: another question, I just ran a six wire unipolar stepper motor with my four wire driver ( not connecting the center wires for each coil) can I just connect the center wire to my supply voltage? and if so will this give me more torque?
    Last edited by Milutiche; 30th May 2012 at 09:11.



    •   Alt30th May 2012, 06:45

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    Re: 555 square wave generator

    Quote Originally Posted by mister_rf View Post
    Some simple stepper motor controllers:



    http://www.eleccircuit.com/4013-and-...stepper-motor/

    Can someone please explain to me the reason for adding diodes in parallel to the Mosfet output???



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    Re: 555 square wave generator

    I think there is a mistake in that drawing. Each diode should be connected between the MOSFET drain and +12V. (Only D2 is drawn correctly).

    The reason for the diodes is because the load is inductive. Without the diode, when the MOSFET switches off, the voltage on the drain will tend to shoot up briefly to a high voltage, which could damage it.
    Last edited by godfreyl; 8th June 2012 at 03:04. Reason: typo



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    Re: 555 square wave generator

    Thaks for that, exactly what I tought. :)



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