Motor current to voltage converter

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Discussion Overview

The discussion revolves around designing a current-to-voltage converter for a motor used in a safe deposit box, with the goal of detecting whether the door is blocked during operation. Participants explore various circuit design options and considerations related to this application.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant suggests using a current shunt resistor to measure the increase in current when the motor is blocked, indicating a potential design solution.
  • Another participant recommends placing the shunt resistor at the tail end of the H-bridge, assuming a DC motor is used, and explains how to measure the voltage across the shunt to calculate current.
  • A different participant proposes using a proximity switch as an alternative method to detect if the door is fully closed, suggesting it might offer additional safety by reversing the motor if an obstruction is detected.
  • There is a request for a schematic to accompany the motor design, highlighting the need for practical guidance in circuit design.
  • One participant questions whether this method is similar to how garage doors detect obstructions, indicating curiosity about the broader application of the discussed technique.

Areas of Agreement / Disagreement

Participants present multiple approaches to the problem, including the use of a shunt resistor and a proximity switch, indicating that there is no consensus on a single solution. The discussion remains open with various suggestions and considerations being explored.

Contextual Notes

Participants express varying levels of expertise, with some identifying as beginners in electronics, which may affect the depth of technical detail provided. There is also a mention of the need for additional research and self-sufficiency in project design.

electronproto
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Hi all..

I'm designing a Safe deposit box..
It use motor to open and close the box..
but i want to know if the door is blocked when closing/opening..

I realize that the current needed for the motor will increase if it's blocked..

I'm using ATmega ADC, but it need voltage input..
so i need a current-voltage converter to know if it's blocked or not..

can someone provide me with circuit and explanation?

thx


Daniel
 
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Current shunt? (There are high-precision < 1 Ohm resistors sold for this purpose)
 
hi.. can u help me by providing the schematic (with the motor)..

I'm still newbie in electronics..

thx
 
You just need to put the shunt resistor at the tail end of your h-bridge. That's presuming that you're using a DC motor here, by the way.

The shunt resistor will have a small voltage generated because all of the current going through the motor will go through it before going to ground (V=I*R_shunt). You just measure this voltage (using the ADC, and maybe an amplifier--remember, it's not a very high voltage when you only have 50 mOhm) and you can calculate the current (or just set a threshold ADC value for a short condition, without having to do any of this math).
 
electronproto said:
hi.. can u help me by providing the schematic (with the motor)..

I'm still newbie in electronics..

thx

You need to do the schematic yourself -- it's *your* project. You should be able to do it with he advice that MATLAB has provided so far, plus some additional research on your own. We do not do your homework or your project schematics for you here on the PF.
 
Just wanted to throw out another posibility if this is not a school project; although using a motor loading circuit that you are designing will work fine. One could use some sort of proximity swith to sense the door not being fully closed.

On second thought, your design might be better in that you could also make it reverse the motor so that you could remove your finger should it get in there.
 
Just a curious side note, but is this how garage doors work when they sense someone (or something) stuck under it? I could see the shunt trick being a quick and easy way to sense something blocking the path.
 

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