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Question about DC motors

  1. Mar 20, 2012 #1
    Hi my name is Rami am from Syria and is my first post here, i'm studying communication engineering and i'm working on a junior project about ( car mirror with memory ) that saves the locations of a car mirror for many drivers ..
    i'm using Atmega-16 to do this with keypad and L293 Motor Driver and LCD
    every thing went well but the PROBLEM is :
    How can i know the position of the DC motor ?? ( read the position )
    how to read it ?? what device ?? what method to have values for motor positions back to Microconroller ??
    I cant add a resistor to bring the value ( rotation ) from motor because i'm working on regular and fixed car mirror ... and normal DC motor .. non-step one
    the solution should exist somewhere in my circuit
    my project reached a dead end
    any useful ideas please ????
    many many many thanks 4 all
    sorry about my English :)
     
    Last edited by a moderator: Mar 21, 2012
  2. jcsd
  3. Mar 20, 2012 #2
    A rotary encoder is a common way to know the position of your motor.
     
  4. Mar 20, 2012 #3
    Thank you DragonPetter but i cant add anything to my DC motor in that mirror ( no place ) its fixed
     
  5. Mar 20, 2012 #4
    Well, there are simpler solutions, but this depends on the position resolution you can accept.
     
  6. Mar 21, 2012 #5
    solutions like what ??? :(
     
  7. Mar 21, 2012 #6
    Have you considered a potentiometer, or photodiodes?
     
  8. Mar 21, 2012 #7
    If there is really NO ROOM in the housing for extra parts you are probably banging your head on the impossible. If there is some room, then first thing would be some kind of limit detectors or switches, and then maybe you can add a few more for in-between detection. Or a disk with a bunch of holes drilled around it's edge so you could get a step count? Having a potentiometer on the drive shaft would be a big step-up from that.

    Failing all that, if the drive system has hard stops at both ends, you can detect the motor current so you at least know when you've gotten to the end. Then you could just count how much time it takes between the stops and estimate the position.
     
  9. Mar 21, 2012 #8
    Good point. You can model your system mathematically and run it in open loop and hope it stays on course. You would have to get your bearing on the position at start up every time, which would basically mean drive the motor to a known point with a photodiode or a physical blocking that causes the current to increase like schip666 mentioned.
     
  10. Mar 21, 2012 #9
    Guys relly many thanks it's great ideas i've never though about current change with limits ,
    is it possible to add a timer... any suggestion IC ? or i can program it with micro ??
    really thank you DragonPetter and schip666
    chears ..
     
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