Subject:
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Re: 3-wire converter for homebrew sensors (fwd)
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 26 Mar 1999 03:43:18 GMT
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Original-From:
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Jim Choate <ravage@*saynotospam*EINSTEIN.ssz.com>
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Viewed:
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1108 times
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----- Forwarded message from Pete Sevcik -----
Date: Thu, 25 Mar 1999 21:00:13 -0600
From: Pete Sevcik <sevcik@flash.net>
Subject: Re: 3-wire converter for homebrew sensors
The angle sensor connected straight to the RCX is non-linear because it is in
series with another resistor located inside the RCX.
During a sense operation, the RCX drives the sensor input from a 10K resistor to +5
volts. Call this resistor R1. The Sensor is a resistor between the input and
ground. (Call it R2). By Ohms law, the voltage across R2 is 5(R2)/(R1+R2). R1 is
a constant, and the voltage aproaches 5 as R2 becomes very large compared to R1.
I wonder if a log tapered pot (audio taper) would correct this problem ?
----- End of forwarded message from Pete Sevcik -----
Actualy you could model it as either a series or parallel, Norton or
Thevenin, depending on whether you want to model the impedence of the actual
A/D as a open or a short. Bottem line, it's non-linear because there is a
fixed value component in the network with a variable component and as a
result the effective impedence, in respect to the source, isn't linear.
As to the linearity, using a audio taper pot was what I would have used.
____________________________________________________________________
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Alexis A. Gilliland
The Armadillo Group ,::////;::-. James Choate
Austin, Tx /:'///// ``::>/|/ ravage@ssz.com
www.ssz.com .', |||| `/( e\ 512-451-7087
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