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RCTIME Baseline — Parallax Forums

RCTIME Baseline

SunflowerSunflower Posts: 48
edited 2005-04-14 02:53 in BASIC Stamp
RCTIME Baseline

Do I need 470 ohm resistors inline with our <85 ohm photo-resistors tracking the sun, to compensate for the 220 ohm pin-protection resistors used in RCTIME?

Comments

  • SunflowerSunflower Posts: 48
    edited 2005-04-13 22:24
    I tried experimentally and found inline 220 ohms worked. My calculations were way off. RCTIME seems like a voltage divider at low sensor ohms, but still gives sensitive results (rather than just a 1).
  • Andy Lindsay (Parallax)Andy Lindsay (Parallax) Posts: 1,919
    edited 2005-04-14 02:53
    Yes, because of the necessary resistor protection to prevent a current surge into the capacitor, there will always be some voltage divider element along with the measured time decay. With photoresistors, it's better to have the the resistance of the cell be much larger than the 220 ohms to reduce the error introduced by the voltage divider. There are probably CDS cells out there with higher resistance ranges as well as filters (sunglasses for your photoresistor). Photodiodes are nice because they have a pretty linear response. See Applied Sensors, available from www.parallax.com -> Downloads -> Stamps in Class Tutorials.
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