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Reading a pot? — Parallax Forums

Reading a pot?

TonyATonyA Posts: 226
edited 2007-08-24 21:27 in Propeller 1
Hi,

Could anyone refer me to info on connecting and reading a potentiometer·using the Propeller.

Thanks,
Tony

Comments

  • TonyATonyA Posts: 226
    edited 2007-08-20 15:32
    Found here:

    http://www.parallax.com/dl/docs/prod/prop/RCTime.zip

    Posted the link in case someone else was looking.
  • rjo_rjo_ Posts: 1,825
    edited 2007-08-20 18:47
    Tony,

    Test it out thoroughly... part of the "education" process is sometimes bumping into things in the dark. The example you found can actually be used as part of a good demonstration that Ohm's Law really isn't a law[noparse]:)[/noparse] Don't blame me... a guy at MIT is pushing this one. I don't have my usual computer at the moment. I'll post a reference when I get back home.


    Rich
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-20 19:01
    rjo_ said...
    ....that Ohm's Law really isn't a law[noparse]:)[/noparse] Don't blame me... a guy at MIT is pushing this one. I don't have my usual computer at the moment. I'll post a reference when I get back home.
    I shall be most interested!

    Ohm's law says that the characteristic curve of a resistor is a straight line.

    It all depends on your definition of a resistor.
    An "ideal" resistor is defined by Ohm's law smile.gif
  • rjo_rjo_ Posts: 1,825
    edited 2007-08-20 19:02
    Yes... but ideal resistors don't exist.

    Rich
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-20 19:30
    rjo_ said...
    Yes... but ideal resistors don't exist.
    So what? So what you choose to call "real resistors" have different characteristic curves. No need to blame Ohm's Law for it!
  • rjo_rjo_ Posts: 1,825
    edited 2007-08-20 20:27
    I didn't blame Ohm's law... a physicist at MIT did that.

    Rich
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-20 21:01
    Well, Ohm experimented with low current DC on medium sized metallic conductors at room temperature.

    Any extreme change of that will lead you to general electro-dynamics if not quantum mechanics...
    There is no such thing as Ohm's law at -275° C (superconductivity) or at 1 GHz (skin effect) or 100 Tesla smile.gif
  • TonyATonyA Posts: 226
    edited 2007-08-20 22:11
    Well, if anyone is looking for info on rctime for the Propeller here is a good source:

    http://www.parallaxinc.com/dl/docs/cols/nv/vol7/col/NV134.pdf
  • TonyATonyA Posts: 226
    edited 2007-08-20 23:16
    Referring to the Nuts & Volts article posted above, I was wondering if anyone could offer some help.

    (I am a prop beginner, and new to programming in general)

    I'm enjoying this article, but came across something I'm a little confused about.

    From what I understand the article explains the creation of an object called rctime, and then shows how you can load this object into its own cog by doing this:

    PUB start(pin, state, zofs, div, rcAddr) : okay

    stop
    mode := 0
    okay := cogon := (cog := cognew(rctime(pin, state, zofs, div, rcAddr), @stack)) > 0

    if okay
    mode := 1

    So "stop" in the above code is a reference to a method? If so, where is the stop method located? (I don't see it in the rctime object).

    Thanks for any help.
    Tony
  • rjo_rjo_ Posts: 1,825
    edited 2007-08-20 23:27
    Good question[noparse]:)[/noparse] I don't see it either.

    Rich
  • TonyATonyA Posts: 226
    edited 2007-08-21 01:06
    Ok, well I downloaded the RCTime.spin object and now the article is making much more sense to me. I see where it is referencing the stop method. The article doesn't show the complete code, for some reason.

    Tony
  • rjo_rjo_ Posts: 1,825
    edited 2007-08-22 17:08
    Tony,

    sorry to clog your thread... but deSilva... a name you should remember... was interested in a reference on the demise of Ohm's law.

    deSilva

    Again... great work on your assembly tutorial.

    I'm home ... finally... so I found the reference:

    http://web.mit.edu/smcs/8.02/lecture9-220k.ram

    This is a lecture by Prof. Walter Levin (He pronounces his name "Lewin") in the open course ware produced by MIT... in this case for physics 8.02. The lecture gives the full derivation of Ohm's law... as well as Prof. Levin's objections to calling it a law.

    What I like most about the Propeller is that a person can actually do his own experiments... without having to first deal with other people's lumped abstractions. Someone should introduce Doctor Levin to the Propeller... he could re-create his entire course around it[noparse]:)[/noparse]

    Rich
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-22 18:21
    High school stuff, but very entertaining, though has some lengthy parts in it smile.gif
    At first I thought: What a preposterous imputation!
    But than I suddenly recognized what electronics is really all about: Getting rid of the heat!


    And the quitessence? Don't put your Prop into a thermos flask!
  • rjo_rjo_ Posts: 1,825
    edited 2007-08-22 18:35
    On the other hand... if you overclock it right... you could heat your coffee or herbal tea[noparse]:)[/noparse]

    The Propeller is the ideal desktop companion[noparse]:)[/noparse]

    Rich

    Dies ist Sekund
  • Fred HawkinsFred Hawkins Posts: 997
    edited 2007-08-22 22:36
    rjo_ said...
    http://web.mit.edu/smcs/8.02/lecture9-220k.ram
    Rich
    Rich,
    What's a .ram thingy? My browser wants to save it.

    Fred
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-22 22:53
    It's a "RealPlayer" file.
  • SkogsgurraSkogsgurra Posts: 231
    edited 2007-08-23 14:53
    deSilva,

    You are probably more right than you think there: "There is no such thing as Ohm's law at -275° C"

    ;-)

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-23 19:03
    I just wondered how long it would take someone smile.gif
    Well I like rounding numbers. -273,15 is such an UGLY value ...
  • rjo_rjo_ Posts: 1,825
    edited 2007-08-23 20:09
    deSilva and Skogsgurra,

    We are way off topic. My apologies to Tony... I think his question got answered?

    As far as I'm concerned there is always room for a little humor.

    There is still hope for Ohm's law...

    There is no reason to assume that resonant coupling does not occur at -273.15... At the microscopic and thermodynamic limits, resistance becomes dominated by ordered couplings... which eat current until saturated. At -273.15 (are we sure this is the right number?)... no resistance can exist, but we know that current can be consumed...

    so, at -273.15C Ohm's law would be true... but only until current is actually flowing[noparse]:)[/noparse] [noparse]:)[/noparse] [noparse]:)[/noparse]
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-23 20:23
    rjo_ said...
    ...Ohm's law would be true... but only until current is actually flowing[noparse]:)[/noparse] [noparse]:)[/noparse] [noparse]:)[/noparse]
    Fine! This is exactly what I learnt fron Prof. Levin's lecture.
    To repeat his reasoning (in my own words):
    Whenever current flows, dissipation takes place, leading to higher temperature, changing the resistancy of the material!

    Every good EE looks for getting rid of this heat: He has to, as he believes in Ohm's law!
    A bad EE does not: He believes in "Magic smoke" smile.gif
  • Paul BakerPaul Baker Posts: 6,351
    edited 2007-08-23 23:10
    Ok guys, there are a growing number of threads that are going off topic in this forum. You guys can discuss the finer points of ohms law, just do it in it's own thread (and preferably in the sandbox since it isn't related to the Propeller).

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
  • deSilvadeSilva Posts: 2,967
    edited 2007-08-24 21:20
    Ohm's law "not related to the propeller"! Tse, Tse...
    But I new it! It's all black magic inside...
  • Paul BakerPaul Baker Posts: 6,351
    edited 2007-08-24 21:27
    It's more of a silvery grey [noparse]:)[/noparse]

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Paul Baker
    Propeller Applications Engineer

    Parallax, Inc.
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