High Freq Pulse Generator with AVR

Discussion in 'Embedded Systems and Microcontrollers' started by xsatria, Nov 12, 2012.

  1. xsatria

    Thread Starter New Member

    May 15, 2012
    Hi Everyone,

    I'm working on project that needs PPS to control
    the Stepping Motor.

    PPS stands for Pulse Per Second,
    currently, with Atmega16A and 16Mhz Crystall
    I can make high frequency generator, but...

    now the problem are time, down-time or rise-time was still
    to long, this situation effects to stepping driver.
    when high turn to low. I want a sharper pulse,

    is there any idea to resolve this?
    or should I make an extra circuit?

    thanks for your help all.

    greeting peace from Indonesia.
  2. BillO

    Distinguished Member

    Nov 24, 2008
    How fast do you need the rise and fall times?

    You do realize the inductance of the motor and capacitance in the drive circuit will probably dictate and upper limit to the slew rate, right?

    If you wanted to clean up the signal coming out of the MCU you might consider some fast comparators.
  3. Papabravo


    Feb 24, 2006
    Something is not making sense. Most stepper motors should run fine at one pulse per second. The rise and fall tome can be a couple of milliseconds without affecting anything.

    Now if you want to run the motor at say 5000 steps per second there are a couple of bigger issues besides rise and fall time. The first issue is mechanical resonance. You have to use constant acceleration (linear velocity ramp) to get from zero velocity through about 200 steps per second up to 500-600 steps per second. To get to higher velocities you need to reduce the L/R time constant with BFR (Big Frickin Reseistors) OR Bi-level drive. Let us say you have a motor which requires 3.2A per phase @ 7 volts. What you need to do is let the phase you are turning on see 40V @ 4A, as the current rises 2.7 A you switch to your 7V @ 25 A supply. When you turn a phase off you catch the flyback and use the 80-90V to hold up the 40V supply. Simple -- piece of cake - Right??