a little help with a pwm circut

Discussion in 'The Projects Forum' started by robertthred, Feb 19, 2016.

  1. robertthred

    Thread Starter New Member

    Feb 1, 2008
    I need help designing a dual pwm circut. I need a circut that will run two 5v motors, but there's a catch... I need one control to control the speed of both and one another control to adjust the difference in speed between the two motors. ie I need, at the extreme, one to run dead slow while the other runs at top speed and vice versa. Anyone have any ideas, PLEASE!
  2. bertus


    Apr 5, 2008

    How will the speed of the two motors be related?
    Will it be in the following order?
    0 100
    20 80
    40 60
    60 40
    80 20
    100 0
    in percentage of speed.

  3. robertthred

    Thread Starter New Member

    Feb 1, 2008
    Yes and the 'overall' control can be dropped if its too big a pain
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    You need your PWM signal to drive two current amplifiers that operate opposite of each other.
    A PNP and an NPN transistor would be my suggestion.
    Drive both with the same signal. One will operate from the positive voltage pulse and the other will operate on the ground or negative voltage part of the PWM signal.
    A single pot can control a 555 timer in this way, but I think you are limited to a 95/5 percent max and min.
    robertthred likes this.
  5. robertthred

    Thread Starter New Member

    Feb 1, 2008
    [​IMG] Ok, cool. I took some electronics courses in Highschool but that was a LONG time ago and I recently started dabbling again. So I would run both the transistors off the same output and just wire each to a separate motor? Any chance to get a diagram? Im rusty as hell at this. this is the circut I currently have breadboarded.
    Last edited: Feb 19, 2016
  6. dannyf

    Well-Known Member

    Sep 13, 2015
    I can be done fairly easily with a mcu.

    Short of that:

    1) use a 555 timer to generate pwm 1, and invert it to generate pwm 2.
    2) use two dual-gang pots + two 555 timers. the first dual-gang pot are in phase and controls the pwm duty cycle; the 2nd dual-gang pot are out of phase and applied to the CV pins to control the differential.
  7. ronv

    AAC Fanatic!

    Nov 12, 2008
    Something like this added to your 555.
  8. Colin55


    Aug 27, 2015
    Simply use a PIC chip and you can read the speed of each motor and control them any way you want.
    I have a number of projects doing this already and it's best done with stepper motors if you want full control.