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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.

DLC
--
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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