Subject:
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Re: calculating sensor resistance (Ohm's Law)
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 7 Apr 2001 01:34:08 GMT
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Original-From:
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Pete Sevcik <PSEVCIK@AUSTIN.RR.saynotospamCOM>
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Viewed:
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708 times
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Lauren,
Your diagrahm is correct. Your voltage assumption is not. On RCX the full
scale is 2 volts to 5 volts, not 0-5 like you have assumed. Try
re-calculating with a 3 volt span.
- pete.
lauren klein wrote:
> I've been helping my little sister with her RCX-intensive science
> project, but we just finished all the calculations and her results seem
> screwy. Does anyone who understands RCX internals and/or Ohm's Law have
> some time to look this over and make sure I've got all everything right?
>
> This is what we've done: We first made a couple of pressure sensors;
> each one has a force sensitive resistor (FSR; same functionality as a
> pot) in series with a 1K resistor.
>
> With these sensors (one plugged into each RCX input), we were able to
> record raw values 0-1023 in the datalog. We can convert these values to
> voltages just by scaling 0-1023 to 0-5, but what I need to figure out is
> the resistance of the FSR that corresponds to each of these voltage
> values.
>
> This is an Ohm's Law question. The problem is that I do not know what
> the inside of the RCX brick looks like. With the information I could
> find on the web, I can only guess that the whole setup looks like this:
>
> inside the lego -----+ my sensor
> |
> +5v 10k | 1k
> +-----/\/\/\/\/--+-- input --/\/\/\-+
> | | |
> --- +-+ |
> - |V| |
> --- +-+ |
> - | |
> | | |
> +----------------+-- input --/\{}/\-+
> ground | FSR
> | (pot)
> inside the lego -----+
>
> In which case it's a series resistance and I can find the resistance of
> the FSR with the following equation:
>
> V 1+pot
> --- = --------
> 5 10+1+pot
>
> But the values I'm getting don't really make sense. I just wanted to
> check, is this the correct formula? And is my picture of the inside of
> the RCX correct?
>
> Thanks so much.
> Lauren
--
Pete Sevcik sevcik@flash.net
Techno-stuff Robotics
http://www.flash.net/~sevcik/
Robotics for FUN !
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Message has 1 Reply:
 | | Re: calculating sensor resistance (Ohm's Law)
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| Pete Sevcik <lego-robotics@crynwr.com> wrote in message news:3ACE6E90.3FA776....rr.com... (...) full (...) That is not true for passive mode. The scale is 0v = 0 and 5v = 1023 in passive modes like touch or temperature. The problem with what Lauren (...) (24 years ago, 7-Apr-01, to lugnet.robotics)
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Message is in Reply To:
| | calculating sensor resistance (Ohm's Law)
|
| I've been helping my little sister with her RCX-intensive science project, but we just finished all the calculations and her results seem screwy. Does anyone who understands RCX internals and/or Ohm's Law have some time to look this over and make (...) (24 years ago, 6-Apr-01, to lugnet.robotics)
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