How to Read the Position of a DC Motor for a Car Mirror with Memory Project?

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Discussion Overview

The discussion revolves around the challenge of determining the position of a DC motor used in a car mirror with memory functionality. Participants explore various methods and devices that could be employed to read the motor's position without modifying the existing setup, which is constrained by space limitations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Rami seeks a method to read the position of a DC motor in a fixed car mirror setup without adding components to the motor.
  • Some participants suggest using a rotary encoder as a common solution for position sensing.
  • Others note that adding components like a rotary encoder may not be feasible due to space constraints.
  • Alternative solutions proposed include using a potentiometer or photodiodes, depending on the available space.
  • One participant mentions the possibility of using limit detectors or switches to determine position, along with a disk with holes for step counting.
  • Another idea involves detecting motor current to identify when the motor reaches its hard stops, allowing for position estimation based on time taken between stops.
  • There is a suggestion to model the system mathematically and run it in open loop, requiring initial positioning at startup using a photodiode or a physical block to increase current.
  • Rami expresses appreciation for the ideas and inquires about the feasibility of adding a timer for position tracking.

Areas of Agreement / Disagreement

Participants present multiple competing views on how to approach the problem, with no consensus reached on a single solution. The discussion remains unresolved regarding the best method to determine the motor's position given the constraints.

Contextual Notes

Participants acknowledge limitations related to space for additional components and the need for a solution that does not alter the existing motor setup. The discussion also highlights the dependence on the resolution of position detection that can be tolerated.

Rami Ak
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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 can't 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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A rotary encoder is a common way to know the position of your motor.
 
DragonPetter said:
A rotary encoder is a common way to know the position of your motor.

Thank you DragonPetter but i can't add anything to my DC motor in that mirror ( no place ) its fixed
 
Rami Ak said:
Thank you DragonPetter but i can't 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.
 
DragonPetter said:
Well, there are simpler solutions, but this depends on the position resolution you can accept.

solutions like what ? :(
 
Have you considered a potentiometer, or photodiodes?
 
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.
 
schip666! said:
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.
 
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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