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Help with photoresistors — Parallax Forums

Help with photoresistors

A.C. fishingA.C. fishing Posts: 262
edited 2006-03-18 20:27 in General Discussion
'm trying to send power from some AA batteries through a photoresistor and drive a motor. The motors drive when I replace the photoresistor with a wire, but no with the photoresistor. I have replaced the photoresistor many times with different kinds of photoresistors but no luck. What is wrong???confused.gifconfused.gifconfused.gifconfused.gif

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-03-18 14:21
    · Are we talking about cadmium-sulphide photocells?
    · A photoresistor will go "low ohms" in presence of light (daylight), but not to 0ohms.· Another matter is that photoresistors are not for running current through, like a switch, being typically 1/8W or 1/16W devices.
    · What you want to do is use it/them as part of a voltage divider and sense the voltage across it.
    · I am providing two experimental circuits, if you are interested in learning.· One is just a basic divider and the other is for use with a STAMP by using RCTIME.

    Post Edited (PJ Allen) : 3/18/2006 2:35:13 PM GMT
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  • A.C. fishingA.C. fishing Posts: 262
    edited 2006-03-18 16:09
    PJ Allen said...


    Are we talking about cadmium-sulphide photocells?
    Huh?? I'm using the same kind of photoresistors that come with the Boe-bot.(I like to use my Boe-Bot)
    PJ Allen said...
    and the other is for use with a STAMP by using RCTIME.
    I'm not using a stamp for this part of the project.(And I don't have a spare for this part either)
    PJ Allen said...What you want to do is use it/them as part of a voltage divider and sense the voltage across it.
    I don't know if you are making this a bit too complicated. Perhaps I wasn't as clear as I should have been. This part of my project only has to make a motor slow (Because less current is coming to it), using a photoresistor
    Hope I'm clear.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2006-03-18 20:15
    A.C. fishing said...
    I don't know if you are making this a bit too complicated. Perhaps I wasn't as clear as I should have been. This part of my project only has to make a motor slow (Because less current is coming to it), using a photoresistor
    Hope I'm clear.
    · Yeah, uh-huh... well, excuse me a minute while I...··
    · OK, boe-bot, you have a good time.
    ·
    · If you're trying to use the "photoresistor" in series with a motor to slow it down, then you go right ahead.· Who am I to stand in the way of such genius?

    · Hope I'm clear.
  • Mike GreenMike Green Posts: 23,101
    edited 2006-03-18 20:27
    You can't do what you want with a photoresistor. The photoresistors have too high a resistance to directly control a motor even when they are fully "on". You have to use them as a sensor for either a microcontroller like the Stamp or, at least, with some kind of an amplifier like a transistor or op-amp.
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