Question about DC motors

  • Thread starter Rami Ak
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  • #1
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Main Question or Discussion Point

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 :)
 
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Answers and Replies

  • #2
828
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A rotary encoder is a common way to know the position of your motor.
 
  • #3
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A rotary encoder is a common way to know the position of your motor.
Thank you DragonPetter but i cant add anything to my DC motor in that mirror ( no place ) its fixed
 
  • #4
828
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Thank you DragonPetter but i cant add anything to my DC motor in that mirror ( no place ) its fixed
Well, there are simpler solutions, but this depends on the position resolution you can accept.
 
  • #5
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Well, there are simpler solutions, but this depends on the position resolution you can accept.
solutions like what ??? :(
 
  • #6
828
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Have you considered a potentiometer, or photodiodes?
 
  • #7
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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.
 
  • #8
828
1
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.
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.
 
  • #9
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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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