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[DPRG] Current Sensing -- How to Do It?

Subject: [DPRG] Current Sensing -- How to Do It?
From: Dennis Clark dlc at frii.com
Date: Mon Jul 19 11:15:57 CDT 2010

I think a collection of Hall effect sensors to detect the car position  
is your least complicated/expensive path. I recommend that you trigger  
at the beginning (or just before) and end of the curved sections since  
those are the places where your speeds will be changing.

Dennis Clark
While traveling

On Jul 18, 2010, at 9:57 PM, "Dick Swan" <dickswan at sbcglobal.net> wrote:

> I kept my kid’s old model slot car race set with the intent to event 
> ually make it computer controlled. I want to run one of the two cars 
>  via computer control and leave the second one for manual control. T 
> hat way you could play against the computer.
> My idea is to split the track powering into several segments each  
> with its own feed from the output of a single H-Bridge used to power  
> the car. I need some kind of detector circuitry for each segment to  
> determine whether it contains the race car.
> There’s a similar need for this detection in model railroading where 
>  I found several approaches for “track occupancy” detection. The  
> best approach seems to be a current sensing detector which is trigge 
> red from the current draw of a motor operating on the segment. Other 
>  approaches include small magnet on the car triggering hall effect s 
> ensor or light sensors interrupted as the train passes over.
> What I couldn’t find is an easy to build circuit – many of them  
> pre-date inexpensive modern single chip current detecting IC circuit 
> s. But I am not skilled enough to design a circuit that uses one of  
> these ICs.
> A further complication that I worry about is how PWM might impact  
> the output – if I’m polling the detector and the poll just  
> happens to be during PWM “off” then it won’t detect any  
> current? I’d like to “smooth” the output
> Can anyone help me here?
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