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Resistor value help

Discussion in 'Electronic Basics' started by Kelly Davis, Aug 3, 2003.

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  1. Kelly Davis

    Kelly Davis Guest

    Hi, I'm trying to do a project that I found on the net for a laser receiver.
    http://www.ews.uiuc.edu/~nshin/PICTS/laser_layout.gif

    First of all I have had some electronics training, but that was years ago.
    I'm just fiddling around with some old parts out of VCR's and the like and
    just doing this for entertainment. My question is about the 100M resistor on
    the base of the phototransistor. I can't find any surface mount resistors of
    this value anywhere. I did see one 100M resistor on a component supply site,
    but it was wire wound and about the same dimensions of a broom stick. I know
    I can add in series to get this but that's a lot of resistors. e.g. 100,
    1Mohm or 10, 10Mohm. Seems like overkill to me. I thought maybe I was
    reading it wrong, or the schematic was wrong, but the parts list says 100Meg
    resistor also. I realize that if my electronics theory was up to snuff I
    could just calculate the appropriate value, but it's not and right now I
    don't care about theory, I just want to build the dang thing and tinker
    around with it whether it works or not. That being said, am I reading it
    wrong or is the value wrong or is it just a big hoax to get me to spend a
    lot of time chasing my tail looking for a non existing part. TIA for helping
    out.
     
  2. That's right; since they're surface mount, and such high resistance,
    they are so small that their value can be changed by the touch of ones
    hand.

    Tom
     
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