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Smart solution for detecting valve limits

Andreas Hansen
Intellectual 410 points
Other Parts Discussed in Thread: DRV8836, DRV5033, DRV5053

Hi

I'm about to design an application that involves a DC-stepper motor (3V DC, 5ohm) that is controller by TI's integrated stepper motor driver DRV8836.

The problem I'm facing is, that I need a way to detect when the valve is closed (at it's limit) such that I can stop the motor.

The application is very power sensitive since it is powered by only a couple of AA batteries.

I have looked at some current measurement mechanisms that is built around sensing the voltage drop of a series resistor, however the solution seems to require too much power.

Any suggestions for better solutions is very welcome.

  • 0
    Guru 22270 points

    Hello Andreas,

    The simplest technique for stopping a motor when it reaches its limit is with a mechanical Limit Switch.  It doesn't require any power.  You can also wire it up to cut off power to the motor as a safety feature.  This would require additional circuitry that would restore power when turning the motor in the other direction.  You will also have to factor in the enertia of the motor to prevent jaming the valve or include some kind of friction gear/plate.

    Thanks,

  • 0 in reply to Greenja
    TI__Mastermind 20985 points
    Yes, a mechanical button is a simple and cost-effective solution.

    Another classic option is to use a Hall-effect sensor and a small magnet attached to the moving part. It'll consume more power than the mechanical switch, but has advantages of never wearing out, being immune to dirt, and it can sense across a short distance if you wish. The DRV5033 is TI's most suitable part.

    Best regards,
    RE
  • 0
    TI__Mastermind 20985 points
    One other thing: sometimes you want to sense 3 positions of a valve. You can do that with the DRV5053, as explained on Page 6 of: www.ti.com/.../slia086